Dr. Mark Hyman is a practicing family physician, medical advisor for Bill and Hillary Clinton, and a #1 New York Times bestselling author of multiple books on nutrition and wellness, including Eat Fat, Get Thin and The Blood Sugar Solution. Dave Asprey is the founder of Bulletproof and the author of the New York Times bestsellers The Bulletproof Diet and Head Strong. The two recently sat down for a conversation about why consuming fat is good, why counting calories is a mistake, and how we’ve been looking at weight loss all wrong.
Mark: You’re a living example that you can lose 100 pounds, keep it off for 10 years, feel good, and not struggle every day.
Dave: When I was in my early 20s, I weighed 300 pounds. I started going to the gym. Six days a week, an hour and a half a day, half cardio, half weights. I cut my calories, cut my fat. But I never lost weight. It’s not because I didn’t try and it’s not because I didn’t want to. It’s because of biology and because, frankly, we’ve been lied to. This idea that you can work off the potato chips you eat, it doesn’t work like that. And when you eat a low fat diet, it breaks your hormones, and it makes you hungry all the time.
Mark: We all know that fat has nine calories per gram and carbs and protein have four. More than twice as many calories. So, if metabolism is a math problem, you just cut out more calories and you’re going to lose weight. That didn’t seem to work for you, [but] then you changed and you started eating more fats.
Dave: I have the original Atkins diet book from the year I was born, which states that eating more fat makes you lose weight. This knowledge has been out there for longer than I’ve been a human being. When you go on a diet like that, you feel amazing and you lose weight and you’re never hungry.
Here’s the alternative. You take this fat person and you give them a bowl of kale. They’re going to be tired and hungry when they’re done eating it because there wasn’t enough energy in the food to power their brain. Where does energy go in the body? Your heart and lungs and liver have to work, and the brain feels like it’s in a constant state of emergency when it doesn’t have enough fat. It literally triggers a hormone cascade.
Mark: Yeah, I’ve seen these guys who look like they came out of a concentration camp with salad bowls this big, completely full, voraciously eating like they’re not getting enough food.
Dave: That’s what’s happening. The idea that somehow eating food with less calories makes you a better person, it’s astounding how backwards that is.
In your car if you put really low octane gas in your car it barely runs. That’s kale. If you put high octane gas in your car it sounds like a race car and it has more horsepower. I want to be the race car.
Mark: Higher octane fuel, that’s fat.
Dave: It is.
Mark: I want to dig into the hormone hypothesis of obesity. If you look at the research that’s coming from [people like] Dr. David Ludwig, it’s showing that weight metabolism is about hormonal balance. If you can figure out how to shut off the insulin signals, which is the fertilizer for fat cells, then you can speed up your metabolism and change your biology without starving yourself. Dr. Ludwig had one study where he put people on isocaloric diets. Same calories, one was 60% fat, one was 10% fat. The 60% fat group burned 325 calories more a day by doing nothing else except eating fat. That’s like running an hour a day by sitting on the couch.
Dave: Ranchers have a ratio for their animals called Feed Efficiency. There’s a synthetic estrogen that’s made by toxic mold that [ranchers] concentrate into a pill called Zeranol, and it melts into the bloodstream in the animal. It increases feed efficiency by 30%, which means that the cows get fat on 30% less calories.
Mark: Because estrogen makes them store fat.
Dave: Yes. If a drug can do that, calories in, calories out is a stupid idea, and it needs to be stamped out.
Mark: In the ’30s and ’40s they were trying to get pigs to gain weight, so they gave them all this coconut oil and antibiotics. Independent of the feed they were eating, the calories, they were gaining weight because their gut flora, which regulates metabolism, was altered.
Dave: The gut flora thing is so important. In The Bulletproof Diet I wrote about this fantastic mouse study they did. They take germ-free mice, with no bacteria in their gut whatsoever, and feed them anything sterile, and the mice were lean and ripped. The second they put a couple of pellets of mouse poop in there, so they get natural mouse bacteria, two weeks later, 60% body fat.
“It’s not because I didn’t try and it’s not because I didn’t want to. It’s because of biology and because, frankly, we’ve been lied to.”
Mark: The whole calorie thing isn’t it. If it’s the hormone hypothesis, then what are the hormones at play here? How do we get smart about regulating the hormones that control our weight?
Dave: One of the biggest hormones aside from insulin is cortisol. We eat sugar and get a spike in blood sugar, followed by a crash. Insulin tells your body to store fat. But during the crash the body secretes cortisol, the stress hormone. Cortisol increases blood sugar and your body thinks you’re going to die if your blood sugar crashes. The brain runs out of energy. Emergency! The cortisol comes up and then adrenaline comes out, which also raises your blood sugar level. All of a sudden you’re like, “Okay, I’m feeling good again.”
Mark: Eating sugar creates a stress response in your body?
Dave: Yeah. It actually causes your body to create something called reverse T3. It takes your thyroid hormone, which tells your body how much fat to burn, and it makes it a reverse one that can’t work. When you have all these energy fluctuations from eating low-calorie, low-fat, you end up [running] on cortisol. Then, you end up having this stress response, and cortisol makes you store fat.
Mark: Cortisol makes you store fat, and it also interferes with your thyroid function, which slows your metabolism. It’s a double whammy.
Dave: I had high cortisol. I had high estrogen, too, because I was eating the wrong fats and I was eating low fat for a long time.
Mark: We’ve got cortisol going up, we’ve got thyroid going down, we’ve got insulin going up making you hungry, storing fats, slowing your metabolism.
Asprey: [And there’s] a hormone called ghrelin, the hunger hormone. It gives you cravings, and your body has an appetite level that’s set at your body weight. [If you] exercise and eat nothing, your hunger levels, your ghrelin levels, will always be up here. The only way to reset your ghrelin levels is to raise ketones in the blood above 0.5. You have to eat less sugar and carbohydrates, not even too many proteins, and eat more fat and some vegetables. Or you fast for a few days and your ghrelin set point goes from fat person down to your current body weight. It turns out there’s a cheat.
Mark: What you’re saying is when you get enough fat, you get ketones, and then it actually turns off the hunger switch in your brain.
Dave: It resets hunger so that the hunger matches your current size instead of your old size. When fat people lose weight, they always have the hunger of a fat person, even when they’re thin. Eventually you’ll give in [because] willpower is a finite resource.
Mark: When you said “ketones” you were talking about a hack. What is that?
Dave: When you go into Atkins or a super paleo low carb [diet], or if you fast for several days, you go into full fat-burning mode, where your body stops burning sugar as its primary fuel source and starts burning fat. [But] most people don’t want to go four days without eating any carbohydrates, and it’s a strenuous diet. Freedom from food is caused by dropping ghrelin. It’s that control of cravings that then leads to more willpower.
Mark: People who are overweight feel so much shame about being overweight, and it’s because they’re given the idea that, “It’s your fault you’re fat. If you weren’t such a lazy person and you just ate less and exercised more, you’d be fine. This is about willpower.” And it’s not.
Dave: When you do it right, it’s effortless. It doesn’t take any willpower at all. You’re just like, “I don’t want to eat that.”
“People who are overweight are given the idea that, ‘It’s your fault you’re fat. This is about willpower.’ And it’s not.”
Mark: What is the story with CCK?
Dave: CCK is a hormone that makes you feel full. And it doesn’t take very much of this fat-burning ketone in the blood to change your levels of CCK. If you can get halfway into this, “I’m fasting, I’m all paleo” thing, just halfway there in terms of fat burning, it throws a switch that turns on CCK. Now, you’ve turned off cravings and you’ve turned on fullness and you walk around going, “Food has lost its power over me.”
Mark: Let’s talk about the Biggest Loser study, which was a front page article in the New York Times. It was based on this study of 6-10 people who went through the Biggest Loser program. They concluded that when they lost weight, they slowed their metabolism down. Then when they gained weight, they were actually at a slower metabolism even than when they started. They were in worse shape. It was a depressing study because everybody got the message that it’s hopeless.
Dave: It’s hopeless to exercise your way to thinness, and it’s hopeless to starve yourself to thinness. It’s not sustainable. When you’re fat, your body is storing energy instead of burning it, which means there’s an energy deficit in the brain. The brain is going to tell you, “Store energy. There’s a famine happening” even if you’re eating enough for there to not be a famine, because it keeps going into fat instead of going into the brain. It’s an energy partitioning problem. Instead of using it, you’re saving it, which creates a shortage, which makes you feel hungry, makes you have these cravings and makes you do this over and over. It’s a vicious cycle.
Mark: [The study] proved the concept of “eat less, exercise more” wrong. Their entire biology was shifted into more fat storage because they were eating a higher carb, lower fat diet, which drove the weight gain. We know that’s how this works. It’s called the insulin carbohydrate theory of weight loss, or the hormonal hypothesis.
Dave: We also have this problem where people love to simplify when they’re making recommendations. They say, “Carbs are bad, protein is bad.” Or, my favorite one, plant-based versus animal-based. It doesn’t make any sense. The same is true when someone goes, “Does it have fat or not?” If it’s got trans fat or margarine in it, don’t eat a high-fat diet of that stuff. If it’s corn oil, canola oil, and soybean oil, those are not biologically compatible with us.
Mark: Breast milk is 25% saturated fat. It’s the most abundant fat in breast milk. If the government’s telling us to eat less than 10% saturated fat, but mother nature is giving us 25% to develop a new human, you’ve got to wonder, right?
Dave: Look what happens when you take a baby and put them on a vegan formula that’s low in fat: neurological developmental delays, lack of bone density. There are millions of well-meaning parents who are cutting fat out of their diet because they have young kids, and they’re actually harming their children. And if you’re not getting enough of these critical fats for your hormones to be strong, it actually weakens the next generation and the generation after that. We are seeing huge declines in fertility, and a part of that I’m absolutely convinced is people eating the wrong fats and not enough of the right fats.
Mark: And they’re eating too much sugar and refined carbs.
Dave: That’s another huge problem. There are parents forcing their kids to eat more fruit. Fruit is full of sugar. It’s basically watery candy with trace amounts of vitamins and fiber. Vegetables are full of stuff that you need. Eating a lot more vegetables and limiting the fruit will change your metabolism.
Mark: What’s your view of meat and is it harmful? Because there have been reports [saying] that it increases risk of cancer and mortality. There are animal studies that look at issues around meat, and there’s the TMAO question with how it affects your gut bacteria. There’s a lot of stuff coming out that we should all be eating less meat.
Dave: Don’t eat meat unless it’s grass-fed and organic. The quality of meat matters, and most people eat too much meat. However, eating no meat and no animal fat is not good. There are very few healthy, thriving vegans over 30.
We just talked about how antibiotics make you fat. They give antibiotics to the cows to make the cows gain weight on less food. Now, those antibiotics are still in, then you eat it, and you’re going to gain weight on less food.
When we went on this weird low-fat bandwagon, a lot of people said, “Well, it’s not working. People are still getting fat. Maybe we should go on high protein diets.” The problem is your body converts protein to sugar to break it down.
Mark: Yeah, if you eat more than the amount that you need to create muscle synthesis, which is about 30 grams per serving, right?
Dave: Yeah, 30 grams per serving, and for the average person, 75-90 grams per day is all they need. But you’re eating the steak from the antibiotic, corn, and soy-fed, mass-produced, tortured animal. Ethically, environmentally, and healthwise, you’ve done something bad. Do not talk to me about whether meat is good or bad until you tell me what the meat ate. Everything before 1950 was grass-fed. And magically, those populations didn’t have the problems we have now.
Mark: The Plains Indians.
Dave: No heart disease at all.
Mark: They had one of the highest per capita centenarians of any population at the turn of the century, and they were eating buffalo. That was the primary diet.
I did a body composition [test, and] I scored way below the normal percentile. I was below the fifth percentile in body fat. They’re like, “We’ve never seen this before, especially in a guy who’s 56 years old.” My Telomere age, my biological age, was 43, which is 13 years younger than I actually am. And I think it’s because I’ve cut out a lot of the processed food, sugar, flour. I ate more fat and my body composition changed.
Dave: It also changed without effort.
Mark: Right, I wasn’t working hard at it. But isn’t the government still telling us to eat less than 10% saturated fat? Doesn’t saturated fat raise your blood cholesterol? How do we reconcile that issue?
Dave: The American Heart Association just changed its recommendations. They now call cholesterol in food, quote, “A nutrient of no concern.” And people don’t hear the message.
“Do not talk to me about whether meat is good or bad until you tell me what the meat ate.”
Mark: But what about saturated fat?
Dave: Saturated fat is stable. It doesn’t oxidize easily. When you eat too much of these polyunsaturated corn oil, soybean oil, and vegetable oil, they oxidize when they’re exposed to heat or air or light.
If you eat these, you will build them into the cell membranes in your body. When they are oxidized, they create free radicals. [So] you’re constantly, chronically inflamed. Then, in order to, say, make efficient use of insulin, a receptor has to push itself through the cell membrane. But, when you put bad fats and trans fats into your cell membranes by eating them, you can’t get the receptors through very effectively.
Mark: Cells can’t communicate with each other.
Dave: Yeah, and you end up getting insulin resistance. That’s not a good thing. Saturated fats, though, when they are not hydrogenated, they don’t create free radicals. They’re stable. They’re the building blocks for cholesterol and hormones. Having more stable fats is part of my strategy to reduce inflammation in the body.
Mark: [But] the prevailing view is that saturated fat causes more inflammation.
Dave: I don’t believe the data’s there for that.
Mark: I couldn’t find it either.
Dave: What I see in Bulletproof Diet people is that they go on the recommendations, which include limiting sugar and removing inflammatory toxins from the diet. What you end up with is this shocking reduction in inflammation. All of the markers of inflammation that are more predictive than cholesterol levels for heart attack risk go down for most people.
Mark: There was one [study] that I saw, where they gave people 50% of their calories as saturated fat. Not only did these people have more lean body mass and lower body fat, they [also] had lower inflammation and lower oxidative stress. Their triglycerides went down, their HDL went up. Their LDL went up a little bit, but the particle size increased, which is actually the good kind of LDL.
[Another recent study] was a meta analysis [that found that] increasing saturated fat levels are associated with a decreased risk of stroke. [In another study,] the highest levels of dairy fat [corresponded to] a 40-50% lower risk of having diabetes.
The last nail in the coffin was the Minnesota Coronary Experiment. You couldn’t do this today, but they took 9,000 patients in a mental hospital, and they gave half of them saturated fat, and half of them vegetable oil. They found that the ones who had their cholesterol lowered the most had the highest [rate of] death in heart attacks.
Even though the vegetable oil lowered the LDL, everything else got worse. You get the oxidation, you get all these problems. They literally buried this study because it contradicted the researchers’ beliefs. They didn’t publish it for 40 years.
Dave: If you don’t have inflammation (which comes from stress, sugar, fructose, bad fats, and more), but you do have cholesterol, you put on muscle mass more easily and your odds of death from all causes of mortality go down, all from having more cholesterol. [Even] your ability to withstand being poisoned goes up because your body will raise LDL in response to toxins in your environment and your food, and it uses LDL to bind to toxins and excrete them. [So] if you have this stuff floating around and you don’t have inflammation, it’s probably protective.
Mark: [So] you’re not worried about doctors saying, “Your cholesterol’s gone up”?
Dave: When people first go on a high-fat, low-carb diet with the right kinds of fat, as the liver is becoming less fatty, oftentimes your cholesterol goes up. Even your triglycerides can go up for six weeks or even a couple months, and then you see changes after that.
If your cholesterol’s 270 versus 220, and you have no inflammation markers whatsoever, your quality of life is going to be amazing.
Mark: As long as your HDL is high and your triglycerides are low.
Dave: Yes, that’s absolutely required.
Mark: People like you who are really thinking out of the box, who are looking at the evidence, who aren’t stuck in old ideas, are actually bringing [in] concepts that are helping millions of people. I really want to thank you for doing the work you do.
Dave: You’re welcome. And never underestimate the power of these three words: butter, bacon, coffee.
Mark: It tastes good, you feel good, you’re not hungry, your brain works better, you get more ripped, and your sex life gets better.
Mark: And it’s not some crazy promise. It’s basic science.
This conversation has been edited and condensed.