Dr. David Ludwig and Jimmy Moore Discuss the Biology of Hunger

“Hunger isn’t just a passing mood, it’s a primal biological response.”

There really might be a secret to weight loss–but it isn’t a magic pill. Dr. David Ludwig, an endocrinologist and researcher at Boston Children’s Hospital, Professor of Pediatrics at Harvard Medical School and Professor of Nutrition at Harvard School of Public Health, recently published a book, Always Hungry? that proposes an alternative approach to weight loss. Rather than seeking to balance calories, restrict indulgences, and pump up exercise, he looks at hormones and the way our fat cells process calories. The results might be the key to long-term weight loss. He sat down with Jimmy Moore, an author, blogger, and podcaster who uses his own struggles and success with weight loss to bring solutions to millions of readers under the moniker “Livin La Vida Low Carb.”

Jimmy Moore: I see myself as an empowered patient who’s taking a lot of the research that people like yourself have been doing for years and trying to translate it into palatable information for the common folk out there. Unfortunately, there are a lot of mixed messages and there’s a lot of convolution of the messages that are out there about health. I’m just trying to shoot straight from the hip for people.

Dr. David Ludwig: Well, go ahead and aim and fire.

Jimmy: I know you’ve been long interested in pediatric health and helping children with fatty liver disease that’s coming on. When did you start having all of these thoughts for this new book? How did that come about?

David: Always Hungry? is aimed at adults but it helps children avoid obesity-related chronic disease. It does it the same for adults.

After weight loss, we know what is going to happen. People will be hungry, their metabolism will be slowing down as their body fights back against weight loss. That is the consistent response to weight loss, which you’re supposed to ignore, but these are primal biological responses that antagonize long-term weight loss efforts. The “calorie in, calorie out” model completely disregards those biological reactions and expects you to just endure hunger and slow metabolism for the rest of your life. That’s why we call the book Always Hungry? It’s a consistent experience on conventional low calorie diets.

Jimmy: I think a lot of times people hear the notion, ‘It’s all about the calories.’ I’m waiting for the day that some scientist decides to test that theory by putting a comparison group of 1,500 calories worth of Oreo cookies versus 1,500 calories worth of meat and vegetables. If it’s only about the calories, wouldn’t it stand to reason that we would see exactly the same results?

Hunger isn’t just a passing mood, it’s a primal biological response.

David: Actually, in the short term you would — if you could actually enforce that. In the short term, if you restrict calories to the same degree, you’ll lose weight at approximately the same rate, taking into account the water. There are some water shifts that will be different on those two diets.

That’s not the issue. We know that calorie restriction can cause a little short term weight loss. At the beginning of the year, there are dozens, if not hundreds of new celebrity diets that promise you’ll lose 30 pounds in 30 days. Those are undoubtedly wildly exaggerated promises but, if you could stick to a low calorie diet you know you’ll lose weight.

The problem is what happens later, after the first few weeks or months. Your body is going to start fighting back with increasing hunger, slowing metabolism. If you keep cutting back calories you only make that situation worse. That creates a battle between mind and metabolism we’re destined to lose. The body goes into starvation mode.

Hunger isn’t just a passing mood, it’s a primal biological response. It’s much more powerful than our willpower. Yes you lose the same weight on 1,000 calories of junk food versus 1,000 calories of high nutrition. But you’ll be feeling entirely differently. Your metabolic state will be different and the likelihood that you’ll succeed for the next two months, let alone the rest of your life, will be dramatically different.

Let me tell you just one study that I think dramatically demonstrates this difference, published in the Lancet in 2004. We put these rats, who were at risk for Type 2 Diabetes, on either a low glycemic index diet or a high glycemic index diet. Same amount of protein, fat, and carbohydrate but just slow digesting carbohydrate versus fast. The high GI animals, the fast acting carb fed animals, wanted to gain weight excessively on the same amount of food. It was like their metabolism was slowing down and they were burning off fewer calories so they were storing more of them.

To prevent that, we did exactly what the conventional paradigm proposes. We put them on a low calorie diet. We restricted their food intake compared to the other group to keep their weights the same. Even in the end of the study, even at the same weight, they had 70% more body fat. Since they weighed the same and they had 70% more fat they had commensurate reduction in lean tissue. Their heart disease risk factors from all that belly fat was sky high. We made the animals ignore their hunger and just eat enough to prevent weight gain and they were still a metabolic mess. This finding completely defies the “calorie in, calorie out” model of weight control.

Jimmy: Unfortunately, I think if you ask most people, “How do you lose weight,” they will immediately gravitate to, “Cut your fat, cut your calories, and exercise.” That’s what has been, for all intents and purposes, propagandized into our heads all these years.

David: The basic premise of my book is: “Overeating doesn’t make you fat, at least not over the long term. The process of getting fat makes you overeat.”

Insulin, I call it the Miracle-Gro for fat cells. Except it’s not the sort of miracle you want.

It’s backed up by a century of research. The basic argument is that the low fat, very high processed carb high glycemic low diet we’ve been eating has raised insulin levels higher than they would ever be in human history. Insulin, I call it the Miracle-Gro for fat cells. Except it’s not the sort of miracle you want.

Jimmy: It’s a bad miracle.

David: A child with Type 1 Diabetes who cannot make enough insulin will invariably lose weight until getting diagnosed for some treatment. That kid could be eating 5, 7, 10,000 calories a day; you can’t gain weight without insulin. In fact, you’ll lose weight without insulin. Put the kid on insulin, enough insulin, and the weight trajectory returns to normal. You dial up insulin, weight gain. You dial down insulin, weight loss. It’s Endocrinology 101. For the rest of us that don’t have diabetes, the way you dial it up or down is based on what you eat. Nothing raises insulin more than highly processed carbohydrates, calorie for calorie.

As we cut back on fat, you know, eat things like the fat-free Snackwells or the low-fat Twinkies, we jack up our insulin. That insulin drives fat cells into a feeding frenzy. They start sucking up and hoarding too many calories from the blood. After a meal they feast but a few hours later the body starts starving.

We think of obesity as a state of excess, too many calories in the fat cells. The real problem is too few calories in the blood stream. The brain sees it, sees that calories are crashing after a meal. They’re locked away in the fat cells. It’s like you’ve put them in the cupboards — the cupboards are brimmed full but they’re locked shut. There’s nothing to eat. So the brain does what it’s supposed to do. It makes you hungry and then it will slow down your metabolism. Then you eat more, and you overeat, and temporarily solve the problem. But those extra calories get siphoned into fat cells. It creates a vicious cycle.

The answer, really, is to ignore calories and focus on the quality of what you eat. Eat in a way to lower insulin and at the same time calm chronic inflammation. That’s the other problem that happens with fat cells.

When that happens, the fat cells begin to open up their doors. These hoarded calories just want to flood back out when given a chance. The body fills with more calories. The brain, perhaps for the first time in years, experiences a more steady dependable fuel supply and says, “I like this”. Your hunger decreases, cravings vanish, metabolism speeds up so you can begin to lose weight with your body’s cooperation. That may be a slower process than with calorie restriction but, without hunger, it’s progressive and sustainable.

Which do you want? 30 pounds of weight loss in 30 days if you could do it, but you’ll struggle for the rest of the year feeling miserable? Or, just lose a half a pound a week but, after a year, you’ll still have lost 30 pounds and will have done so in a much nicer way to your metabolic rate?

Jimmy: In light of everything you just described, why is hunger looked at as a positive in the context of a health regimen? I’ve heard from a lot of so-called people in the diet realm that, “A little bit of hunger is okay, it means your body is on the right track.” Or are they wrong?

David: I think it’s a cultural delusion. Hunger is a primal metabolic sign that the concentration of calories in your blood is low. What does the brain care most about? Fuel supply. If the fuel supply to the brain is interrupted for a second, you’re going to have a problem. You’ll lose consciousness and after a few minutes you’ll have a seizure, coma, and if that continues you die.

We have deeply ingrained mechanisms that date back hundreds of millions of years to prevent inadequate fuel supply to the brain. Hunger is the first sign that there is a metabolic problem.

Humans don’t do well with deprivation. There’s no reason for it. Clearly we were not designed genetically to be gaining weight generation after generation.

Another thing the body does if you don’t eat is secrete stress hormones. Cortisol, epinephrine, glucagon, growth hormone. That will begin to yank calories out of storage so you’ll have enough calories for your brain but, if you keep going through these cycles of a metabolic crash followed by stress hormone secretion, you take a toll on your metabolism that is probably not good for your lean body mass. It increases cardiovascular disease risk factors, and diabetes risk factors.

Humans don’t do well with deprivation. There’s no reason for it. Clearly we were not designed genetically to be gaining weight generation after generation. Something is going on in our environment. The most likely factor, and there’s a lot of research to support it, is the highly processed diet especially with the fast acting carbohydrates that do a number on our metabolism by raising insulin so much.

Jimmy: I don’t disagree with you that diet and especially these refined carbohydrates are the biggest culprit, but I wonder if continuous exposure to those refined carbohydrates over a period of years, maybe even decades, makes you that much more sensitive to the effects of even healthy carbohydrates like vegetables and fruits, even more sensitive to things like stress and other lifestyle issues that would impact your weight and make you hungry as well.

David: That’s a great question. Let me tell you about a research study we just published and then how we’ve designed the program to address that very perceptive observation. In the same study in JAMA [The Journal of the American Medical Association] in 2012, we took 21 subjects, brought their weight down and put them on the three diets: Low, moderate, and high-carb, and low, moderate, and high-fat too — just in reverse order. It was randomly assigned but, of course, some people will have been randomly assigned to receive the low-carb diet first. We found that if they ate the low-carb diet first, then the high-carb, low-fat diet didn’t seem to have much adverse affect on their metabolism. In other words, when they ate that low-fat diet second, their metabolic rate didn’t drop that much. When they ate the low-fat diet first, it plunged.

Suggesting that once you spend some time on a higher quality diet, you may be able to reprogram your metabolism to tolerate more carbohydrates in a sustainable way. In our study we found that lasts for at least a month. It may last much longer.

This conversation has been edited and condensed.