Dr Rupy: Is chicken healthier than beef?
Dr Kevin Mackey: No.
Dr Rupy: If I eat any amount of red meat in my diet, am I harming my health?
Dr Kevin Mackey: No, I think some red meat is acceptable in a healthy diet.
Dr Rupy: Are all saturated fats harmful to my health?
Dr Kevin Mackey: Not all of them.
Dr Rupy: Is a 100% plant-based diet the healthiest diet for most of us?
Dr Kevin Mackey: I would say it depends.
Dr Rupy: Okay. Does eating a high protein diet impact my kidneys?
Dr Kevin Mackey: The evidence is inconclusive, but suggestive that that is not the case within reason.
Dr Rupy: Okay. Can red meat fit into a heart-healthy diet?
Dr Kevin Mackey: Yes.
Dr Rupy: Do you need red meat to get iron?
Dr Kevin Mackey: Not necessarily.
Dr Rupy: Hi, I'm Dr Rupy. I'm a medical doctor and nutritionist. And when I suffered a heart condition years ago, I was able to reverse it with diet and lifestyle. This opened up my eyes to the world of food as medicine to improve our health. On this podcast, I discuss ways in which you can use nutrition and lifestyle to improve your own wellbeing every day. I speak with expert guests and we lean into the science, but whilst making it as practical and as easy as possible so you can take steps to change your life today. Welcome to the Doctor's Kitchen podcast. If you ordered a steak at a restaurant, are you essentially ordering a heart attack or a nutrient-rich whole food? There are few foods that spark more debate than red meat. It's been blamed for heart disease, cancer, and diabetes, but some people praise it for being high in iron, zinc, vitamin B12, and of course, quality protein. So, if you add red meat to your plate, is it helpful or harmful? Whether you eat meat or avoid it completely, I think you're going to find today's conversation cuts through the noise of social media and clears up a lot of confusion in the nutrition space. And I wanted to disentangle the obvious issues surrounding environmental concerns of eating animal products from today's discussion and simply talk through the nutrition data as we have it. It's given me a lot to think about when it comes to recommendations for people as well as how concerned I might be about red meat consumption overall. Today we're chatting with researcher and academic Dr Kevin Mackey, who specialises in clinical studies on nutrition, metabolism, and chronic disease risk factors. He's also an adjunct professor at Indiana University School of Public Health, a master and past president of the National Lipid Association, that's a big deal, and a fellow of the American Heart Association and the Obesity Society. Dr Mackey has participated in over 300 clinical trials and published more than 250 scientific papers, books, and book chapters. Today you're going to learn about whether red meat is actually unhealthier than things like poultry, what red meat really does to your cholesterol, your blood pressure, or your long-term health risk, whether red meat is a source of unhealthy fats and what fats they actually contain, the different types of red meat and which ones are less healthy than others, how much red meat you can safely consume if you choose to consume it at all, and also where the largest amount of saturated fat comes from in the diet. We also talk about what Dr Kevin suggests to do to lower cholesterol, we talk about seed oils, plus high protein diets and the myths about their relationship to kidney disease, reducing longevity, and increasing one's type two diabetes risk. The four big takeaways that I got from this episode were that moderate amounts of around 50 grams per day of unprocessed lean red meat in the diet seems to be fine. Diet quality and the addition of whole unprocessed foods is much more important. High protein is super important in middle-aged and older adults, which I was quite pleased to hear that from Dr Kevin, as I've written a whole book called Healthy High Protein about this very subject. And why we should be cautious about the four white poisons: sugar, salt, saturated fat, and refined starches. There are a couple of terms that we band around right at the start and throughout, so I want to define those so anyone who's coming to this podcast without any knowledge of studies can follow along. The first is observational studies. These are studies where researchers watch and record what happens in real life without trying to change anything. So, for example, they might track people's diets and see how their health changes over time, but there is no control. So it's harder to ensure that we know or actually tease out what's caused any changes that we observe. Those are observational studies. On the contrary, we have randomized control trials or RCTs. These are a type of test or investigation or study where people are randomly split into groups and they receive different interventions or treatments or no treatment at all. That's a placebo control trial. These types of studies help researchers determine if a treatment or intervention actually causes a certain effect by comparing the outcomes between the groups in a fair and controlled way and monitoring for whether the outcome is actually significant or not. And there are a few statistical mechanisms by which we're actually able to ascertain a true difference or whether something can just be down to chance. And the last thing is insulin sensitivity. You've probably heard me talk about insulin sensitivity before in the podcast, but I want to define it again. This refers to how well your body responds to the hormone insulin that's released from the beta cells of your pancreas and it helps control blood sugar. If you are sensitive to this hormone, your body uses insulin really efficiently and it keeps blood sugar levels stable with moderate amounts or appropriate amounts of insulin being released from the pancreas because everyone responds to insulin in the appropriate way. Poor insulin sensitivity, also referred to as insulin resistance, means that your body has to produce a little bit more insulin because your body has trouble responding to it. Your cells aren't responding to the same signal. And this can lead to higher blood sugar levels over time and increase the risk of conditions like type two diabetes, as well as the negative impacts of having higher amounts of insulin coursing around your body as well, because insulin at high levels can have deleterious effects too. Hopefully, observational studies, randomized control trials, and insulin sensitivity, these are the only terms that need clarification, but you know what? If it is a little bit over your head, send us a message on Twitter or YouTube. You can also watch today's podcast. We're always happy to give some extra explanations to you. And you know what? If you want to speak to virtual Dr Rupy, download the Doctor's Kitchen app and hit the button on the homepage that says call virtual Dr Rupy. You can speak to me, or something that sounds like me, and ask me about these things. Oh, Rupy, you mentioned observational studies on the podcast. Can you define that for me? Or you mentioned red meat. What do we mean by red meat? Dr Rupy or virtual Dr Rupy is on call 24/7, housed in the Doctor's Kitchen app. It's a little bit Black Mirror for me, but the response has been pretty phenomenal. So, if you haven't tried having a chat with virtual Dr Rupy, it is just the first bit of AI that we are putting into the Doctor's Kitchen app that also has over a thousand healthy recipes to help you with all your health goals, whether it's lowering cholesterol, improving your brain health, or just generally getting variety and inspiration for keeping your meals for your family as healthy as possible. Go download it. There's a free trial as well. And of course, the podcast is sponsored by Exhale, my favourite coffee. I'm chief science officer for Exhale, and if you want to try Exhale for free, just click the link on your podcast player wherever you're listening to this. They will send you a free bag of Exhale coffee, no postage, no payment, no card details, for you to try what healthy coffee tastes and smells like. They source it from high altitude crops, so the polyphenol levels of coffee are higher. They independently lab test to ensure that it's free of any toxins and pesticides. It is an incredible, incredible product. And the way they do their, the way they create their product, the way they do business is absolutely astounding. They're a B Corp, they're wonderful people, Kirsty and Al. Check out Exhale coffee. I'm drinking it right now. On to my podcast, all about whether red meat is actually that unhealthy with Dr Kevin Mackey. I really do hope you enjoy this and you can check us out on YouTube as well.
Dr Rupy: Let's get started. Hopefully you're nicely warmed up after those questions. I know that it's tough, you want to go into a lot more of the nuance and the detail. Why don't we talk about red meat in the public eye and overall health? Because there's definitely a suggestion or a belief that red meat is something that should be a luxury and actually if you do include it in your diet, you probably not doing the best for your health. Where did this come from and and why is it portrayed in this way?
Dr Kevin Mackey: Well, I think the history in part relates to saturated fat because red meats contain saturated fat which raises cholesterol levels. And I think also there has been a view that red meat has negative impacts on things like risk factors for diabetes and so forth. And mostly that comes from observational evidence. So population studies where people consume a diet, they report in a food frequency questionnaire and some other way what they're eating. And so one of the problems with that type of study is that people self-select. And so people who eat a lot of red meat also tend to have adverse health habits. And so they tend to be less physically active, they're more likely to smoke, they have higher body mass index, lower average levels of education, and all of these things are associated with adverse health outcomes. Now, I'm an epidemiologist by training, so my training is in evaluating population-based study evidence. And so early on in my career, I got involved in a study comparing red meat to white meat, poultry and fish, with regard to effects on cholesterol levels. And I went in fully expecting that we would see that red meat increased cholesterol levels relative to white meats, and that is not in fact what we found. And then subsequently, I've done numerous studies with red meat. And what we find is compared to poultry as an example, there's no difference with regard to effects on risk factors for cardiometabolic disease, basically cardiovascular disease and diabetes. And so I think that it's complicated. I do think that we don't have all of the answers, but I also believe that in the US, for instance, the average intake of red meat is about 1.8 ounces a day of unprocessed red meat. The question of processed meat is a little more complicated, but I think that that is a reasonable intake. I'm not suggesting people go out and eat a lot more than that. But from the studies that we've done, eating that quantity of unprocessed red meat does not adversely affect cardiometabolic risk factors, but with the caveat, it always depends on what you compare it to. And so I do believe that the dietary guidelines for Americans and they're similar in other countries, that emphasize whole grains, fruits and vegetables, nuts, seeds, legumes, non-tropical oils, and I would add seafood to that, those are reasonable recommendations. So I'm not suggesting people eat more red meat, but I am suggesting that red meat can be part of a healthy diet with an emphasis on unprocessed red meats.
Dr Rupy: Let's dive into a bit more around these observational studies. Our audience are not largely research-based and a lot of people may not have read a full study before. So when we discuss observational studies, it might not be the audience's understanding that we can control for some of those risk factors that you mentioned earlier amongst people who tend to consume more red meat. So if we look at those red meat consumers and we can control for some of those confounding variables like smoking, exercise, etc, that would bring someone's risk of heart disease higher. What do we see?
Dr Kevin Mackey: Well, the difficulty there is when you say control for, what you mean is statistically control for. And so I have a story that I tell a lot. In 1996, I went to the International Congress on the Menopause in Sydney, Australia, and the keynote speaker started her talk by saying, the question at this point is not whether postmenopausal estrogen protects against heart disease. We have 40 observational studies that shows that women who take postmenopausal estrogen have 40% lower risk for heart disease. The question now is how it works. And so then sometime later, a study that both of us were involved in, the HERS trial, showed in fact that women after a myocardial infarction or heart attack, given estrogen, postmenopausal women with a progestin, were not protected. And then subsequently, the Women's Health Initiative study confirmed those results. So postmenopausal estrogen was not protective. So then the question is, well, why? Why did these observational studies suggest one thing and then the randomized controlled trials where there was an intervention and the intervention was randomized, in other words, people were selected at random to be in the control group or the active group, why did that show something different? And the answer seems to be that statistical control for risk factors was not enough. And there are various reasons for that. We don't measure all of the risk factors. The ones that we measure, we don't necessarily measure with high precision. So if you talk about physical activity as an example, asking people questions about how active they are is not necessarily a good reflection of how active they really are. And so there are a lot of challenges. And in many cases, these observational studies do give us the right answer, but in some cases they don't. And so the strongest evidence, I think, is related to those places where we have both observational studies and randomized controlled trials to give us the answer. And when those results align, then I think we can make the strongest recommendations. So as an example, a Mediterranean diet pattern has been shown in a couple of large studies, PREDIMED and CORDIOPREV, to protect against cardiovascular events. And so I think we can make strong recommendations about that. I think about other dietary recommendations, we have to be a little more cautious and a little more sceptical if all we have is observational evidence or observational evidence plus evidence from intervention studies that look only at risk factors. So I think some caution is warranted.
Dr Rupy: Okay. Let's dive into some of those risk factors actually before we go for because I've heard you talk about an anagram, an acronym for cardiovascular risks in the past. Is it flash GI or flash GL?
Dr Kevin Mackey: Flash glee or flash glick. So I'll list out what those are. F is family history, L is for low HDL cholesterol, A is for age, S is for smoking, H is for hypertension or high blood pressure, and then GLI is glucose and that's glucose in the blood or sugar in the blood and it relates to more than just glucose. It's glucose and insulin resistance and sort of regulation of glucose in the blood. And then lipids, apoB containing lipoproteins. We usually talk about LDL cholesterol, but it's a little more complicated than that. And then I for inflammation, and I would add a C to that for coagulation. So these are all of the factors that have been shown to be associated with cardiovascular disease risk, and some are modifiable, some are not modifiable. And of course, you can't change your family history or your age or what have you. And so those that are modifiable, I think the goal is to maintain them in an optimal or healthy range. And so that's my main focus is identifying the risk factors and then maintaining them in an optimal range. And diet influences many of those risk factors.
Dr Rupy: Okay. So if we dive into red meat and we observe, we look at cardiovascular risk factors through those different components that you've just articulated there, where is the strongest evidence that red meat is actually having a detrimental impact and where are you satisfied that the effect is either not seen in the in the randomized control trials or it's neutral?
Dr Kevin Mackey: Well, I would say the strongest evidence from observational studies relates to risk for diabetes. So higher red meat intake is associated with greater risk for diabetes. And so when I look at observational evidence, I say, what are the four key elements that we need to consider in evaluating that evidence? So it's strength, consistency, dose response, and then biological plausibility. And so strength is, you know, how strong is the association? Smoking and lung cancer, very strong association. Consistency, do you find the same relationship across different countries, different investigators, different cohorts? Um, dose response, uh, you know, is higher exposure associated with greater risk or greater protection if it's a protective factor. And so with smoking as an example, heavy smokers have much higher risk of lung cancer than light smokers. And then we look at biological plausibility. And that's where sometimes the evidence breaks down. And when it comes to red meat and risk factors for diabetes, the studies that we've done and others have done, acknowledging their limitations because they're intervention studies that are randomized, but looking at risk factors, not at actual incidence of diabetes. But the studies we've done have shown that compared to poultry as an example, you don't see any worsening of risk factors for cardiovascular disease or diabetes when you feed red meat as compared to poultry. Now, there are limitations, so I don't want to say that we have the final answer on this. Um, and there are some proposed mechanisms that would connect red meat intake with diabetes risk, but at least in shorter-term intervention studies, we're not seeing any adverse effect. And so what I would say is that you always have to ask compared to what. So compared to poultry as an example, we don't see any adverse effect, although in observational studies, you don't see a relationship of poultry intake with diabetes risk, you do see that for red meat intake, but I worry that you aren't controlling for everything. Now, if you compare, for instance, red meat intake to intake of plant sources of protein, then, you know, that's a different story and there are mechanisms through which, say, nut intake as an example, which would be a plant source of protein, may be associated with lower risk of diabetes. So I would say that red meat intake, when consumed in moderation, is fairly neutral, and then there are some other dietary factors that have favourable effects. So you have to consider, you know, always what you're comparing to.
Dr Rupy: Got you. So just to summarize for the audience because this is quite a lot to unpack there. Looking at observational studies, you do see a connection with red meat consumption and an increased risk of diabetes. When you compare red meat and poultry, you don't see any differences. And just going back to the observational studies, you also don't see that signal with poultry consumption. However, when you compare red meat to plant-based proteins, would you say, so nuts, seeds, soy protein, there is a favourable effect of the plant-based ingredients compared to red meat, but there isn't an increased risk of red meat on the diabetes risk. Have I got that correct?
Dr Kevin Mackey: Right. So, so red meat compared to poultry, for instance, to me, with regard to risk factors, looks fairly neutral. For plant sources of protein, they often come along with other things. So legumes, as an example, come along with viscous fibres that have a favourable effect. Um, various plant-based proteins will have unsaturated fatty acids and we and others have shown that higher consumption of unsaturated fatty acids improves insulin sensitivity. So, I don't want to give the message that, you know, you should just go out and eat as much red meat as you want, you don't need to consume plant sources of protein. I do advise people to follow a healthy dietary pattern that conforms with the dietary guidelines for Americans recommendations. And I think on average, the American public is not consuming enough of the recommended foods. Again, I'll repeat that, whole grains, fruits and vegetables, nuts, seeds, legumes, and non-tropical oils. Um, so I'd like to emphasize more eating those things. Um, but you can fit red meat into a healthy dietary pattern, and I think that's that's my message, moderation. Um, also, we'll talk, I think later about processed meat. I have more questions and concerns about processed meats, which tend to be sources of saturated fat, sodium, and then have preservatives in them where I'm not sure we always fully understand the effects of some of those compounds.
Dr Rupy: Yeah, yeah, we're definitely going to go into that. In terms of the criteria that you mentioned earlier, so strength, consistency, dose response, biological plausibility, is there a dose response with red meat that you've observed at all? So for someone who is having, what you mentioned earlier, 1.8 ounces of red meat, which I'm struggling to convert into metric at the moment in grams.
Dr Kevin Mackey: About 28 grams per ounce. So I'm not going to try to do the math in my head, but 28 grams per ounce.
Dr Rupy: Okay, so that's about 50 grams of red meat per day, give or take, which isn't very much at all. Um, would you see an increased risk if someone was having, let's say, double or triple that? Is that something that we observe in in some of the RCTs?
Dr Kevin Mackey: So, in the RCTs, no, but we have to be careful because in the RCTs, we're really looking at risk factors and not at actual incidence of diabetes. So that's one of the challenges. Uh, in the observational studies, we do see a relationship. Every 50 gram per day increase in red meat intake has been associated with about a 13% increase in risk of developing type two diabetes. Um, having said that, I would also say that we have to be a bit careful because again, there may be residual confounding. So those people who eat more red meat tend to have adverse lifestyle habits and so I think we can to some degree control for that statistically, but I'm sceptical that we can fully control for all of those issues.
Dr Rupy: Yeah. Yeah. And going back to that point about moderation, so if we agree that the math is sort of right with 50 grams per day, that's about 350 grams per week, which is, you know, a good sized lean steak, let's say of rump or um, whatever lean beef you want to consume. That's not very much. It's about like a a good handful per week. Is that the the sort of amount that you would say is a moderate amount?
Dr Kevin Mackey: Right. So we say that a serving of red meat is about three and a half ounces. And so having red meat say three times a week, one serving three times a week is reasonable, um, level of intake. And the 1.8 ounces a day is the average intake in the US, but there are some groups who consume quite a bit more than that. So young men as an example tend to consume more than that. And so my recommendation is sort of moderation. Um, in moderation, unprocessed or minimally processed red meat can be part of a healthy diet. Um, a lot of the studies that we've done have been with larger intakes because if there is an adverse effect, we want to be able to pick it up. So we are often feeding people two servings a day of red meat. And compared to foods with refined carbohydrates or poultry, we don't see adverse effects on the cardiovascular risk factor profile or the risk factor profile for diabetes. Um, I'm not necessarily recommending that people consume that much. I think that to stay within the recommendations, um, you know, the current level of intake of unprocessed red meat is not excessive.
Dr Rupy: Yeah. And I know, I know you you would be saying this as well, but I I guess looking at the totality of the diet is also very important. If you are having those whole grains, vegetables, fruits, nuts, seeds, non-tropical oils, that I'm I'm hopefully is is going to be ingrained to people's minds by the end of this podcast, um, is is as important as as the dose of red meat if you choose to consume red meat at all.
Dr Kevin Mackey: Yep, absolutely. A healthy dietary pattern has lots of health benefits and I would say we don't fully understand all of the health benefits. Um, when you consume those recommended foods, you're taking in all kinds of compounds, things like polyphenols and other compounds that we don't fully understand, but we do know that they're associated with favourable health outcomes. We need randomized controlled trials. I'm disappointed that we don't have more of them looking at actual disease incidents, but having said that, I think that we can make recommendations based on the available evidence while acknowledging the limitations of that evidence.
Dr Rupy: I want to dive into some of the biological plausibility arguments because certainly from what I hear, people present these mechanisms as almost set in stone that this is what is going on when somebody consumes red meat. Um, I'm sure you've come across this and perhaps debunked a whole bunch of these, but TMAO or trimethylamine oxide, um, red meat being inflammatory, uh, the heme iron perhaps having a negative effect as well. What are some of the the the biological mechanisms that you've unpacked and and which ones do you think hold true if if any of them at all?
Dr Kevin Mackey: Sure. TMAO, I think is something that has been studied. We're actually in fairly early days with regard to studying that. And we do see that when people consume red meat, TMAO tends to go up. That's not universal. It doesn't happen in every study. When people consume poultry, it doesn't necessarily go up. But when people consume fish, they're also seeing an increase in TMAO and fish consumption has been associated with lower cardiovascular disease risk. So, there are some proposed mechanisms and I don't want to discount those, but we don't really see increases at the levels of red meat that are recommended and the average levels that are consumed. And so that's one of the important things within a reasonable level of intake, we're not seeing that increase in TMAO. And when it comes to heme iron, there are, you know, various proposed mechanisms, but what I go back to always is what do we have with regard to data? And that may be observational, it may be from randomized controlled studies. But I think that for a chunk of the population, the concern is more about not getting enough iron. And so, especially younger women, um, I think also protein intake is suboptimal in a substantial portion of the middle-aged and older population. And plant proteins are fine. Uh, plant proteins, you have to consume a bit more of plant protein generally, um, to get the essential amino acids, um, that would be equivalent to the amino acids in either red meat or poultry as an example. Uh, but it's fine. And so what I say is that when it comes to protein intake, uh, middle-aged and older people are probably consuming less than an optimal amount of protein. Uh, the recommended dietary allowance in the US is 0.8 grams per kilo per day. I think optimal is higher than that, probably in the range of 1.2 to 1.6. And so, um, having some animal sources of protein and plant sources of protein will be, it'll be easier for someone to get that amount of protein if they combine those sources. Now, with regard to heme iron, um, I think that uh, for some people in the population, that that may be problematic, especially those people who um, may have a genetic variant that causes them to store excess iron. And so, you know, that's a small slice of the population, but again, at reasonable levels of intake for most of the population, I just don't think it's a problem. Um, I would recommend, uh, again, a bit outside my area of expertise, but with regard to cancer risk, I would recommend that red meat not be charred, um, because I think some compounds are generated by charring of red meat that can potentially be problematic. So, uh, how the red meat is cooked and prepared is an important aspect, uh, and, you know, is something that people should consider. Um, but, you know, with most people and the way that most people consume red meat, uh, 1.8 ounces a day is not excessive.
Dr Rupy: Okay. So just to summarize for the audience because this is quite a lot to unpack there. TMAO is a byproduct of gut microbe digestion of choline and betaine, um, which are some components that you find in in in these products in in red meat. Heme iron, not so much of an issue that we've we've uh we've debunked that or unpacked that. Um, what about saturated fat? Uh, red meat gets the uh the reputation of being very high in saturated fat and something that we should be limiting. Is that is that true?
Dr Kevin Mackey: It's true, but complicated. And so it isn't just the saturated fat that one consumes, it's what other fats are consumed. And so we know that saturated fats tend to raise LDL cholesterol. Unsaturated fats tend to lower LDL cholesterol. And so when you look at red meat, uh, so I'll take beef as the most commonly consumed type of red meat, roughly half of the fat in beef is saturated. And then about 30% is stearic acid, which is a saturated fatty acid that doesn't raise cholesterol levels. And then most of the rest is 12 to 16 carbon saturated fatty acids that do raise cholesterol levels. But when you put all of that into an equation, um, that predicts the effect on LDL cholesterol, you find that half of the fat is monounsaturated, which tends to lower LDL cholesterol. 30% is stearic acid, um, that is neutral. And then the remainder is mostly cholesterol raising fatty acids. So the predicted effect is neutral to have no impact. I will point out that all meats contain cholesterol and cholesterol has a modest effect to raise LDL cholesterol levels in the blood. And in our meta-analysis that we published, I think it was 2018, I believe, we found the same thing that a meta-analysis found in 1997. And that was that each 100 milligrams per day of dietary cholesterol raises LDL cholesterol by about 2 milligrams per decilitre. And I won't try and convert that into millimoles. So, there is a modest effect of dietary cholesterol, but in beef, as an example, the fatty acids in beef would have a predictive effect of zero. Now, this past week, I presented results at the American Society for Nutrition meeting from a study where we put people on two servings a day of beef compared to two servings a day of poultry. And we found that, it was a crossover study, so people went through both treatments. What we found is at the end of each, they had exactly the same LDL cholesterol level, exactly the same, to the milligram per decilitre. And that's what we found in a study, much larger study, for which we published the results, I think in 1999. So, we know that poultry versus beef, no difference with regard to effects on LDL cholesterol. But if you compare poultry or beef to say, you know, nuts or tofu or tempeh or seitan, you'll have a lower level of LDL cholesterol because of the plant proteins and the unsaturated fatty acids in those plant sources that lower LDL cholesterol. Uh, but when it comes to poultry versus beef, no difference.
Dr Rupy: So this is going to be really surprising, I think, for a lot of people because very like my own, very much like my own experience in in med school, I definitely left with this idea that red meat high in saturated fat, you want to you want to uh lean more into the poultry and replace red meat with poultry and that's a a better uh way of eating for your heart health. But this is untrue and it's it's not new, like you just said, from the 90s, we've actually known about the the equivalent effects on cholesterol of these two different uh meat products. If you wouldn't mind, for the listener's sake, would you mind just giving us a little bit of a biology lesson in the difference between saturated fats and unsaturated fats as they are in beef? And you mentioned the differences between the 12 and 16 carbon chain lengths of saturated fatty acids and why those may have different biological effects because I don't think many people understand the the nuance of of what you just mentioned.
Dr Kevin Mackey: Sure. And this is a bit complicated, so I hope I enlighten more than confuse here. But uh, there are three basic types of fats: saturated fats, monounsaturated fats, and polyunsaturated fats. So, saturated fats are a carbon chain with no double bonds. And so they tend to raise LDL cholesterol. And we know that eating saturated fats lowers the number of LDL receptors on the liver. And when you do that, you raise LDL cholesterol. Unsaturated fats tend to have the opposite effect. They tend to lower LDL cholesterol. And so that's true for monounsaturated fats, like you find in things like olive oil and avocados. And then it's even more true for polyunsaturated fats, um, like you find in corn oil and safflower oil and soybean oil and so forth. Now, polyunsaturated fats have kind of two main types, omega-3 and omega-6. We consume more omega-6 from plant oils than we do omega-3s, which can to some degree come from plants, but mainly come from seafood. And uh, so omega-3s and omega-6s have somewhat different biological effects and I've spent a good chunk of my career studying the biological effects of omega-3s, omega-6s, monounsaturated fatty acids and saturated fatty acids. So, okay, you've got unsaturated fatty acids that tend to lower LDL cholesterol, you've got saturated fatty acids that tend to raise LDL cholesterol. So when you look at the diet overall, it's the balance between those that is most important. And that is something that's missed by many because they focus on saturated fat and say lower saturated fat. Well, in the US, about 11% of energy in the diet comes from saturated fats. The recommendation is less than 10%. And if you were to cut that in half from 11% down to 5 and a half percent, you would lower LDL cholesterol by 3 to 5%. Now, 3 to 5% is important, but I think that that's only part of the picture. If you were to raise intake of unsaturated fats, you would have an equally um effect in the an equal effect in the opposite direction. And so, uh, you know, what I say is, okay, we need to be concerned about saturated fat in the diet. We don't want to consume too much of it, but we'd also like to emphasize sources of unsaturated fats. And those are plant sources, things like nuts and avocados and seeds and non-tropical oils. And so it's a balance and I think that the focus has been much too much on just lowering saturated fat and not enough on consuming those foods that tend to lower LDL cholesterol. And I'll point out that there are other foods, um, viscous fibres like you find in legumes will lower LDL cholesterol. Plant proteins will lower LDL cholesterol. This is a surprise to many people, but all proteins tend to lower LDL cholesterol, but the effect is larger with plant proteins. And uh, so I think that we've kind of narrowed in on saturated fats and demonized them. And I think the American public as an example is eating more than is recommended, but that's only part of the story. We're not eating enough of the foods that are recommended that will balance that out by providing unsaturated fatty acids, proteins, especially plant proteins, and viscous fibre. Um, and then I'll add one more thing, which is that excess body weight uh tends to raise LDL cholesterol. It raises triglycerides even more. Um, but, you know, when you think about what can you do to manage your cholesterol level, well, in part, it's lowering saturated fat and cholesterol intake, that's part of it, but it's also raising unsaturated fats, raising intake of dietary fibre, losing excess body weight if a person's overweight or obese. And increasing intake of plant proteins. Uh, so all of these things uh will have effects and it's the balance that's important.
Dr Rupy: Great. Okay. So going back to the beef fat, uh, uh, topic, you've got these mixture of different types of fats in many different products, including beef. Half the fat in beef is saturated and the rest of it is unsaturated. Have I got that right so far?
Dr Kevin Mackey: Mainly monounsaturated.
Dr Rupy: Mainly mono. And out of the 50% of which is saturated fat, 30% of the saturated fats are stearic acid. And stearic acid appears to have a neutral effect on cardiovascular health. I believe it's the same saturated fat that you find in chocolate. Is that right?
Dr Kevin Mackey: It is found in chocolate. And the 30%, I can't remember whether 30% is 30% of the total fat or 30% of the saturated fat. It's one or the other. But regardless, a chunk of the saturated fat is stearic acid. Stearic acid is actually converted in the body to oleic acid, a monounsaturated fatty acid. And so it has a relatively neutral effect on LDL cholesterol. But, you know, we'll call it uh, you know, roughly uh 35% or so of uh the fat in say beef tallow is cholesterol raising fatty acids, but they're balanced by either neutral or cholesterol lowering fatty acids. So the fat in beef is not what's raising cholesterol levels. It's mainly the cholesterol content of beef that is raising cholesterol levels in the blood.
Dr Rupy: Very interesting. Okay. So with those collection of different fatty acids, again, we're sort of postulating here or hypothesizing, perhaps this is why we see a neutral effect in your studies when people consume a moderate amount of red meat.
Dr Kevin Mackey: Right. So in the study I just mentioned where I presented the results last week, we gave an immoderate amount. You know, we gave two servings a day of either red meat or poultry. And the red meat did have more saturated fat in it. So, uh, in that condition, about 11% of the energy in the diet came from saturated fat, which is pretty similar to uh the average American diet. And in the poultry diet, only 8% came from saturated fat. But because of that balancing effect of the other fatty acids in beef, the effect on LDL cholesterol compared to poultry was neutral. It was, as I said, exactly the same level at the end of our four-week feeding period.
Dr Rupy: Wow. Wow. I think it's going to be really surprising for a lot of folks here because of this sort of idea of, you know, poultry being a cleaner, less saturated fatty, a meat with less saturated fat in it. So this is really interesting. In terms of the different types of fats that you find in beef tallow, because beef tallow is having a bit of a moment right now. So this is similar to the the fatty acid profile that you just mentioned there. You're not suggesting that tallow is something that we can have in the diet, uh, without, you know, any negative consequence, or is it something as long as we're not having it in our coffee, is actually reasonable as a as a fat to to use in cooking?
Dr Kevin Mackey: I think that most people are not consuming enough unsaturated fatty acids relative to saturated fatty acids. So I'm not a fan of switching, as some restaurants have done, to beef tallow as compared to an unsaturated type of oil or an oil that's higher in unsaturated fats. Um, I think that the effect on cholesterol levels depends on the balance. And so, um, I also think there are some concerns about reusing cooking oils so that they become oxidized. I think that is a potential problem. Um, I don't know how much of a problem, but uh, I think that's a theoretical concern. So, I'm not a fan of using beef tallow for cooking french fries, for instance. Um, and in general, uh, I think, you know, french fries are fine occasionally, but I don't think people should be uh, consuming uh french fries, uh, you know, twice a day, um, as I know some people who do that. Uh, and so I think it's all about balance in the diet and I think in general, I talk about the recommended foods, um, and the recommended foods, I'll repeat just for emphasis, whole grains, fruits and vegetables, nuts, seeds, legumes, non-tropical oils, and I would add seafood to that. But then we also talk about tongue and cheek, the four white poisons. And I say that as hyperbole, these are not things that you need to eliminate from the diet, but they are consumed in higher amounts than recommended. And that's saturated fat, salt, refined starches, and added sugars. And so in the average American diet, for instance, people are eating too much of the four white poisons, not enough of the recommended foods. And so what I'd like to see is people making shifts so that they're eating more of the recommended foods and replacing foods that are higher in the four white poisons, um, again, tongue and cheek, uh, with those recommended foods.
Dr Rupy: In terms of the contribution of foods to the amount of saturated fat, um, that we consume typically in the diet, and I take your point that, you know, it's not just about reducing saturated fat in the diet, it's about increasing monounsaturated fats and looking more holistically about what you're including like whole grains, fruits, vegetables, nuts, seeds, non-tropical oils, and seafood. Um, where is the biggest contributor of saturated fats to the diet if it doesn't appear to be uh red meat?
Dr Kevin Mackey: A lot of saturated fat is consumed in mixed dishes, um, and foods, pizza is actually a source of saturated fat. I love pizza. I think uh, in moderation, pizza is absolutely fine. Um, but it's also found in uh processed foods, um, and so saturated fats mainly, but not exclusively, come from animal products. So dairy products and meats, but they also come from tropical oils like coconut oil, palm oil, palm kernel oil. And what has happened to some degree in recent years is there's uh been a removal of trans fats or industrial trans fats from the food supply. And I think that is a good thing. But one of the uh things that has happened is there's been more use of tropical oils, um, that are more saturated. And so they can be helpful in the sense that from a food science standpoint, they allow longer shelf life because unsaturated fats tend to get oxidized and um, you know, cause the food to become rancid. And uh, so I do think that the food supply has changed and labelling really helps with this. And so it is true that uh, in general, people are preferring foods that have um, less than half of the total fat being saturated fat, uh, in foods. And I think that's a good thing and we've seen average cholesterol levels in the population go down. And partly that relates to removal of trans fats, which raised cholesterol levels. And partly it relates to more unsaturated fats in the diet. There are other reasons as well. But again, it's all about balance. And so, uh, processed meats, um, high-fat dairy products, um, unprocessed meats, and then tropical oils are the main sources of saturated fat in the diet. And so, you know, it is a challenge. Um, you have to read labels if you want to keep your saturated fat intake at recommended levels, less than 10% of energy. Um, but I think it's just as important to get a balance of saturated and unsaturated fats.
Dr Rupy: Got you. Okay. And you mentioned earlier about increasing protein and how that reduces cholesterol. Is that across the board or there are there are certain proteins like um, uh, proteins from from plants like soy beans, edamame, um, those kind of products that would reduce cholesterol further?
Dr Kevin Mackey: It does seem that all proteins, if they're replacing carbohydrate in the diet, will lower LDL cholesterol. But plant proteins seem to have a larger effect and we don't fully understand why. And so we did a study some time ago and we had a great hypothesis. And so this is another elegant theory ruined by the pesky data. So we did a study and I'll describe the study, it's a little bit complicated. So we thought that soy protein was partly lowering cholesterol by binding bile acids. So bile acids are made out of cholesterol and so they're released into the gut and then reabsorbed. And so if you don't reabsorb them as much, then the liver says, oh, we need more bile acids and so it uses cholesterol to make those bile acids. And so there's a drug, a class of drugs called bile acid sequestrants. So in our study, we said, okay, here's a group of people, we're going to take some baseline measurements. We're going to give them a bile acid sequestrant drug to see how much LDL cholesterol lowering we get. And sure enough, the drug worked as anticipated. If I remember correctly, it produced about an 18% reduction in LDL cholesterol. Okay, great. Then we had the subjects go through two periods, uh, one where we added milk proteins to the diet and the other where instead of milk proteins, we added soy protein. And our hypothesis was that soy protein would increase excretion of bile acids and that would explain the cholesterol lowering effect. And so, lo and behold, the milk proteins did lower cholesterol and the soy proteins lowered cholesterol about twice as much. So, in rough numbers, let's call it 5% and 10%. But there was no increase with soy protein in bile acid excretion. So our elegant hypothesis was ruined. That wasn't the explanation. We don't know what the explanation is exactly, but we know that's not it. So, you know, Thomas Edison inventing the light bulb did these thousands of experiments and someone asked him once, you know, you've failed thousands of times in trying to invent this. He said, no, I haven't failed. I've just uh eliminated, you know, thousands of things that don't work. So, we eliminated one hypothesis. That wasn't uh the explanation. We don't really know what the explanation is, but it is true for soy protein and for other plant proteins that they lower LDL cholesterol more than animal proteins for reasons we don't fully understand. And having said that, um, this is one of the reasons that I say, you know, those recommended foods. So, um, seeds, uh, nuts, legumes, and so forth, bring plant protein, they also bring fibre often and unsaturated fatty acids, all of which are things that are going to have favourable effects. But part of the favourable effect is the plant protein.
Dr Rupy: So, in that study, you got an equivalent amount of protein from milk and soy. We know it's not the bile acid impact, so that's not the mechanism. Could it be the fibre in soy or like isoflavones, so some of the the the phytochemicals that you find in soy products? Could that could that be some of the reasons?
Dr Kevin Mackey: I have a good answer. No, because we used a soy protein isolate that had the isoflavones stripped out and was an isolate, so it contained no fibre. So it wasn't the fibre, it wasn't the isoflavones, it wasn't bile acid binding. What we don't know what it was. And it did, you know, the effect and just to be completely accurate, um, although LDL cholesterol is what people usually talk about, I like non-HDL cholesterol better because it's a better predictor of risk. And that's just total cholesterol minus HDL cholesterol. So, the effect was again about 5% for the milk proteins and about 10% for the soy protein. Um, and it was only statistically significant for non-HDL cholesterol. The difference for LDL cholesterol, I think was, you know, P of 0.06 or something, which means very close to statistically significant, but it was definitely significant for non-HDL cholesterol.
Dr Rupy: Got you. So, gosh, okay. So we don't know why soy the plant protein has a more of an effect because if we're literally just looking, I mean, so so the soy protein isolate is just a collection of amino acids that have been derived from soy and the milk protein, I'm assuming you were using like a whey or a casein powder?
Dr Kevin Mackey: It was total milk protein, so it's a mixture of whey and casein.
Dr Rupy: And again, that that lowered LDL cholesterol because we replaced carbohydrate essentially with milk proteins and that's been shown in other studies like Omni Heart is a good example of a study where they replaced carbohydrate, 10% of energy from carbohydrate with a mix of proteins and that lowered LDL cholesterol and non-HDL cholesterol. We just don't know why. We don't know why proteins are doing this and why plant proteins seem to have a larger effect than animal protein. So, if there are any uh aspiring nutrition scientists out there who want to study this, uh, it's ripe for investigation.
Dr Rupy: That's that's super interesting. Um, let's end on a bit of a protein rapid fire, uh, section because uh, I know you were part of a review paper looking at um, high protein potential harms. Um, looking at some of the uh, claims that you find not only in, you know, the sort of social media sphere, but also uh in in in papers as well. Um, I literally just wrote a book called Healthy High Protein because I, like you, feel that middle-aged and older adults uh could do with more protein around that 1.2 to 1.6 grams coming from uh a mixture of both plant proteins and animal-based proteins for ease. Um, but there is a bit of a bit of a backlash because there is a lot of um ingrained belief that protein is going to or more protein is going to damage your kidneys, it's going to impact your heart, it's going to uh lead you to have more uh a high risk of type two diabetes. So, why don't we go through some of those uh claims at the moment. Does high protein impact your bones? Does it make your bones more brittle?
Dr Kevin Mackey: In fact, I would say the evidence suggests the opposite. And uh, this isn't my primary area of expertise, but I was recently at a protein workshop where some of the top protein experts in the world attended. We all gave presentations. My presentation related to effects of higher protein intake on insulin sensitivity and kidney function. Uh, so I can talk about those in detail, but Dr Connie Weaver gave a presentation on bone health and that's her main area of expertise. And uh, her summary would suggest in fact that higher protein intake, you know, within reason, uh is associated with more favourable effects on bone metabolism and outcomes related to bone.
Dr Rupy: Okay. So this idea that higher protein results in uh an acid-base imbalance, so you you change the sort of pH of um your your blood that drives um a negative calcium balance, so peeing out calcium. This is completely untrue and it's not something that we've seen in in studies.
Dr Kevin Mackey: And so, I'll, you know, defer to other people with more expertise, but uh, Connie did cover that in her talk. And uh, so while there may be some increase in calcium excretion, um, what is most important is the balance in bone. So bone, uh, the infrastructure of bone is largely protein and then mineral is laid down, you know, on that protein infrastructure. And uh, so bone health is not just determined by the mineral content, but also by the protein content. And uh, her studies, some of which are animal studies, um, but using very sensitive techniques, she's also done many studies in humans as well, would suggest that uh, bone metabolism is improved by higher protein intake. And again, um, when we talk about higher protein intake, I think almost all of the studies are protein intakes that are above the recommended daily allowance in the US of 0.8, um, but, you know, very few of them are above 1.6. And so we're talking about higher protein intakes, but usually still, you know, less than 20% of daily energy or so.
Dr Rupy: Got you. Okay. Uh, why do some people believe that a high protein diet can damage their kidney and why is that untrue?
Dr Kevin Mackey: Well, this goes back to something called the Brenner hypothesis. I think it was uh initially published in the 1980s. And when you give rodents a high protein diet, uh, you see increased glomerular filtration rate. And so, you know, essentially a higher protein diet means the kidneys have to filter out more solutes and so you have to filter more in order to deal with that higher protein load. And so the hypothesis is that you're overworking the kidneys and over time that will damage them and that can lead to problems. And so that does seem to be true in rodents, but then you look at other species like uh swine and you don't see that same effect. And then there have been quite a few studies in humans, but I have to acknowledge that the studies are generally less than two years in length. And when you look at those studies in humans, what you see is that you get no, you do get an increase in glomerular filtration rate, but um, then you don't see that decline over time up to about two years of study. Um, and then when we look at observational evidence, there was a paper published fairly recently that looked at healthy adults and adults with chronic kidney disease, so moderate chronic kidney disease, not severe. And in that study, they looked at mortality and what they found is higher protein intake was associated with lower mortality, especially in the very oldest group in the study. Um, and that was true for people with and without kidney disease. And so, uh, a higher protein intake was associated with lower mortality up to the highest protein intake group that they studied was um, 1.6 grams per kilogram per day. And then in addition to that, there was a recent meta-analysis on protein intake and development of kidney disease. And what that study found is higher protein intake was associated with lower risk of developing kidney disease, not higher risk. Now, I have to point out that the highest levels of intake were still less than about 20% of energy from protein. So these weren't very high protein diets, but observational, we have to be careful, but in general, I think the evidence does not support an adverse effect of higher protein intake within reason on kidney health. Um, and so, you know, what I would say is most middle-aged and older adults should be more concerned about inadequate protein intake, not over intake.
Dr Rupy: Yeah. And and and finally, looking at type two diabetes risk, I think there's this idea of if you have more protein in your diet, it's going to be damaging insulin signalling. Um, I think we can say that about saturated fats. If you're having excess amount of saturated fat in the diet, it can lead to a higher risk of type two diabetes, but protein, and maybe this is where the sort of red meat protein confounding is coming in in people's understanding of this. Um, but why is that untrue? Why is a high protein diet between 1.2, 1.6 grams of protein per day not associated with a type two diabetes risk?
Dr Kevin Mackey: So this is where things get a little complicated and again, it relates to balance. So there are studies that show that when you feed whey protein, for instance, a milk protein, um, weight loss increases insulin sensitivity, but when you give whey protein, that seems to prevent the increase in insulin sensitivity with weight loss. There are also some studies showing directly that uh higher whey protein intake seems to impair insulin sensitivity and that would increase risk of diabetes. But here's where it gets complicated. So we did a study, for instance, where we used egg protein and unsaturated fatty acids. And so we replaced 8% of carbohydrate energy with egg protein and another 8% with unsaturated fatty acids, and we saw a 24% increase in insulin sensitivity. Now, there was another study, um, in which they used cereal fibre. Cereal fibre increased insulin sensitivity. And then a moderate protein intake, about 20% of energy from protein, um, did not seem to interfere with that increase in insulin sensitivity. So, it is true that there are some studies suggesting adverse effects on insulin sensitivity, a key risk factor for diabetes, but when you combine the higher protein intake with cereal fibre, with unsaturated fatty acids, you, you know, the higher protein doesn't seem to prevent the improvement in insulin sensitivity. So it's a little complicated and it probably relates to balance in the diet. And so that's why I say, you know, focus on those recommended foods so you're getting a balance of fibre and unsaturated fatty acids and a higher protein intake, which seems to have some benefits. Um, and I think that the higher protein intake seems to be less of a concern if you're getting enough of the other things.
Dr Rupy: On that note, let's ask you your favourite whole grain, fruit, vegetable, nut and seed and non-tropical oil. What's your favourite whole grain?
Dr Kevin Mackey: Well, whole grains, you know, I eat a lot of whole grain bread and I tend to eat bread that has lots of grains in it. So the particular bread that I eat the most of has 21 grains in it. So I can't pick a favourite. It's like trying to pick your favourite child. Um, you know, fruits, I eat lots of uh fruits. I eat citrus and I eat lots of berries, which are high in polyphenols. Um, uh, nuts, seeds and legumes. Uh, so I eat lots of almonds, lots of pecans. Uh, as far as uh seeds go, not quite sure what seeds I eat the most of. Uh, and legumes, uh, I uh, you know, try to eat a lot of a variety of beans uh to get the fibre and uh, so I, you know, try to walk the talk. What I recommend people do, I try to do myself.
Dr Rupy: That's epic. That's great. We have a thing here at the Doctor's Kitchen called getting your daily BBGs, beans, berries, greens, seeds and nuts. Uh, so we try and take that off just a handful of each cooked every single day and it's a nice little reminder.
Dr Kevin Mackey: I should call out avocados. I eat lots of avocados and uh, so, uh, you know, every sandwich I eat has avocado on it.
Dr Rupy: You must be paid really well. Avocados are pretty expensive over here in England.
Dr Kevin Mackey: They're not cheap in the US, but uh, I, you know, I I I like them and uh, you know, nutritionally, uh, we've done studies with avocados, uh, they uh fill the bill.
Dr Rupy: Yeah, no, they're phenomenal. They're like uh, these are powerhouse ingredients. They're like uh, the amount that we are, we tend to spend on supplements, we should be spending on on whole foods like that. Um, Kevin, this has been great. Thank you so much for your knowledge. You know, hopefully people are going to understand the benefits of whole grains, fruits, vegetables, nuts, seeds, legumes, non-tropical oils, and be aware of the four white poisons. Those are phenomenal takeaways.
Dr Kevin Mackey: Great. It's been a been a pleasure. Uh, really like to get the the word out. Um, I'm a research scientist, but I don't feel as though my job is done until I've communicated to the people who can use the information.
Dr Rupy: Amazing. Amazing.
