Nutrition is a controversial topic. Recently, the Clearer Thinking podcast host Spencer Greenberg invited Dr Gil Carvalho of Nutrition Made Simple fame to talk about nutrition. Here are some of his insights, paraphrased:  

Why are nutritional insights so contested?

• These things are rarely black and white. The strength of the confidence we have in a certain direction goes up gradually as the evidence mounts in a given direction. That’s kind of how science works in medicine and biomedicine in general.
• Reproducibility is key. It’s really the currency of biomedicine because of the multiple variables. There are multiple populations, there are multiple conditions at baseline.
• If you run a randomized controlled trial, it’s one experimental design; it addresses certain questions. If you look at cohort studies, it’s a slightly different angle. You can do experiments in model organisms like lab animals or test tubes. You can answer different questions there. So, it’s really by putting all the pieces of the puzzle together that you get to see the big picture.

What is a healthy diet?  

• Currently, the most validated dietary pattern is what’s called a traditional Mediterranean diet. Fish, seafood, fruits and vegetables, some whole grains, some dairy, there’s not a whole lot of ultra-processed junk foods or fast foods. Olive oil and mostly unsaturated fats.
• There are at least three truly large randomized trials looking at Mediterranean-style patterns with thousands of people over years and looking at different outcomes like the number of heart attacks and even things like cancer. In general, the traditional Mediterranean diet is very powerful at improving these outcomes.

Should people concern themselves with getting the ideal fat, protein, and carb ratios?  

• We see people who are low-fat, they fear fat, they’re terrified of fat. But then a lot of times what we see is they end up eating more of the wrong type of carbohydrate to compensate for removing the fats. We see the same thing with low-carb. Low-carbs are petrified of carbs. They go and eat more of the wrong types of fat and other foods. A more empowering mindset is to focus on the positives, focus on the foods that have the highest quality. What are the healthy sources of fat that you can have in your diet? It’s not trans fats, it’s not Twinkies or McDonald’s. It’s going to be things like salmon, seafood, olive oil, walnuts, Greek yogurt. What are the healthiest sources of carbohydrates? It’s not going to be candy or soda or artificial syrups with a lot of refined sugar added. It’s going to be things like eating a mango, eating a pear, eating a bowl of lentils, some quinoa, some broccoli sautéed in olive oil, and mixing the best carbs with the best fats. There’s no need to fear those carbs or those fats.
• Everybody agrees that refined carbohydrates are not great. I’m not afraid of eating a cookie once in a while. It’s not a staple of my diet. It’s not a daily thing, it’s not even a weekly thing. But if I feel like having a cookie once in a while, I do it. I’m not worried about it because I’m focused on the healthiest foods that are populating my diet. And these things around the edges that I do once in a blue moon, they’re not what’s going to sway your health.
• You can probably put together a low-fat diet or a low-carb diet if that’s your personal preference, and you can design it in a way that probably can support all your aspects of health by doing exactly what we talked about, by favoring the high-quality fats and the high-quality carbs.

What are your thoughts on ketogenic-type diets?

• You’ll see weight loss with any diet that eliminates a lot of foods that people normally eat. The more radical the elimination, the more consistently you see weight loss. The problem is you have a trade-off between the power of weight loss, but also how difficult it is for most people to stick to these diets long-term. So, we see that consistently in trials, whether it’s a very low-fat diet or a very low-carb diet. Some people do very well and love it, but those seem to be a minority. And those people become the evangelists that love the diet and talk about it in high praise, and that’s great; it works for them. The problem is when we look at unbiased studies that just randomize people, the majority fall off the wagon within months to a year. They can’t stick with these diets. And then they put the weight back on, or they lose the gains.
• It’s very good for weight loss, good for control of Type 2 diabetes and glucose levels. Again, if done with attention to the quality of these foods, the low-carb diet, the keto diets get a bad rep for raising cholesterol and raising these things — people being at cardiovascular risk. I think most of the evidence is telling us very clearly that it’s because of the choice of the types of fats. If you have the right fats, unsaturated fats, fatty fish, seafood, olive oil, walnuts, you can improve your lipids on a low-carb diet.
• There’s also something to be said about the uncertainty of most of these diets long-term. So, if we talk about a diet that’s very low-fat or very low-carb, there’s quite a bit of evidence short- and medium-term, up to maybe a couple of years. But we don’t really know what happens to people if they’re on a ketogenic diet or an extremely low-fat diet or many of these popular diets for 10 or 20 years.

Is meat healthy or unhealthy?

• We do see a lot of difference between, for example, processed meats and unprocessed meats. We see a difference between red meat and other types of meats, for example. And we see a difference depending on the level of intake. We also see a difference depending on the type, even within unprocessed red meat, whether it’s fatty or lean.
• But the idea that having any red meat in your diet is unhealthy is not compelling. But based on the evidence we have, having a diet that’s very high in fatty meats, to the point where it’s elevating your risk factors (your ApoB, for example), in all likelihood, that will raise your cardiovascular risk.
• Your blood work is one way to know your risk. Your family history is another way. If you’re eating a diet with a bit more meat than the next guy but your blood work looks amazing, I would worry less. And if your family history is also unremarkable for those things, it’s also a sign that you may have a stronger resistance if you tolerate it better.
• Less processed forms, leaner cuts, whiter meats, fish, which essentially is a type of meat are healthier. Fish has better health outcomes, probably because of the types of fat that it contains.

Is saturated fat unhealthy?

• If you compare saturated fat to, for example, refined carbohydrates, you don’t see a difference in cardiovascular risk. If you compare it to trans fats, saturated fat even trends to looking better. If you compare it to unsaturated fats or whole carbohydrate sources, you tend to see a bit higher risk for saturated fat.
• If you look at what scientists are actually saying, it’s to favor foods that are richer in unsaturated fats. It’s not to avoid saturated fat like the devil and go eat whatever you want instead, which is what Western populations tend to do. And then there’s other details like types of saturated fat. Also, some types of saturated fat don’t raise cardiovascular risk, like the saturated fat in dark chocolate, for example, which is called stearic acid.

What about processed meat?

• The hazard ratios are higher, so the risk of diseases looks higher. It’s more compelling; it’s also more consistent in different studies. The level of confidence is higher for, say, bacon or beef jerky — these types of processed red meats. Things like heme iron and nitroso compounds, and Neu5Gc; all these things that are created during the processing that are thought to increase, for example, colorectal cancer risk and also maybe cardiovascular disease.

How much protein do people need?

• Protein needs vary by age and by level of physical activity. 1.6 grams of protein per kilo of body weight. And that’s kind of a threshold where they see muscle growth being maximized. That’s more for people who are actively doing resistance training, who are lifting weights, who are trying to put on some muscle. For people who are just looking for maintenance, 1.2 is another number that is suggested.

Does too much protein damage the kidneys?

• I don’t think the kidney damage theory has much evidence behind it; it’s mainly been debunked. Maybe one caveat would be if someone has kidney disease already, if they have problems with their kidneys, or maybe they have a family history of kidney problems.
• It also depends on where you’re getting your protein from. If you’re getting your protein from certain sources and not others, getting protein from fish and seafood and lentils and things like that in a Mediterranean dietary pattern is one thing. Getting protein from bacon and whatever else is not the same case at all. So, I would make that caveat about the source more than the protein itself. I am not convinced that protein itself is harmful.

Should everyone try to reduce their sugar intake?

• Most Westerners would do well to reduce their refined carbohydrate intake. Why exactly sugar, refined carbohydrates, is problematic isn’t entirely figured out. here are lots of possibilities. One thing is just the caloric density; they are less satiating.
• Also, they have lower fiber. So, all in all, you’re going to tend to overeat calorie-wise before you’re full, before you’re satiated.
• The ideal is to look for whole foods. So, whole grains as close to nature as they are found: steel-cut oats, quinoa, corn on the cob. You can’t go wrong with those. Now, I realize that not everybody is going to be doing that exclusively. So, people want to have some bread or they want some pasta. Normally, I’m going for the whole grain. 100% whole grain is a safer choice; basically, it means nothing was removed; all the components are still there, it just got ground down.

Is obesity harmful?

• The distinction here is between population level and individual level, and this is a question that people always raise with any risk factor. So, when we talk about these things and risk of disease, we’re always talking about population level. At a population level, we have abundant evidence with Type 2 diabetes, with mortality, with cardiovascular disease, that as people become more overweight and obese, the risk of all these things goes up, even cancer. So, populations exposed to that risk factor — I would say obesity is a strong risk factor — have more incidence of these diseases. That does not mean that every obese individual will suffer from those diseases.
• If you are obese but your lipids are really good, your glucose levels are good, all these things, your blood pressure is good, it’s a sign that you have a stronger constitution; you tolerate it better than the next guy whose blood work is a nightmare. If your family history is solid, your family members are also obese, and they live to an older age. Okay, maybe you guys have won the genetic lottery.

Is measuring ApoB preferred over LDL cholesterol when determining cardiovascular disease risk?  

• It’s a more validated, more rigorous metric of heart disease risk than LDL cholesterol and HDL cholesterol. The measures that we normally get — HDL cholesterol, LDL cholesterol, and triglycerides — are basically the types of fats being carried around in our blood. They are reflections; it’s almost like looking in the mirror or at a shadow of the things that really cause disease.
• ApoB measures the number of what’s called a lipoprotein, which is essentially the vehicle that carries the fat around in the blood. Most of the evidence in the cardiovascular research field points to ApoB as the number of these lipoproteins being the main metric of risk or the main cause of risk, not the content of fats. So that’s why ApoB is a more reliable measure of risk than LDL cholesterol. For example, you can have somebody whose LDL cholesterol is a bit high but whose ApoB is normal. Population-wise, they’re not at higher risk. And vice versa, if their ApoB is high and LDL cholesterol is normal, they are at higher risk.

What about glucose?

• Glycemia or the blood fasting glucose is one metric. You can also measure your glucose after meals. One thing to bear in mind, that a lot of people don’t realize, is you can have problems with your glucose metabolism for years before your glucose goes up. So, you can have insulin resistance building up. It’s undeniably a red flag if your fasting glucose is high. But if your fasting glucose is normal, you could still have a problem with your glucose metabolism and just not have gotten to that point yet. Basically, your body will try to hold things together, sometimes for years, by producing more insulin to get your glucose out of your blood. It will be able to compensate. But then, you get to a certain point where you lose that ability.

What is a sustainable way to lose weight?

• There are foods that are more satiating and nutrients that are more satiating. In general, higher protein foods are more satiating. Fiber is another trigger, probably less potent than protein but still a factor. Caloric density or energy density is another factor. So, foods that are very energy-dense are less satiating. Whole foods, foods that are not ultra-processed, are usually a good rule of thumb because they are less calorically dense. Foods that contain more water, foods that contain more fiber, and foods that contain more protein.