“If you don’t have metabolic health, you don’t have anything” Robert Lustig (Interview)

Robert Lustig is a distinguished pediatric neuro-endocrinologist renowned for his extensive research on the intricate relationship between hormones and the brain. Over the past three decades, he has devoted himself to unraveling the mysteries of the obesity and diabetes epidemics, as well as the phenomenon known as metabolic syndrome. Although retired from clinical practice, he remains deeply involved in research, policy development, consulting, and legal matters, holding a master’s degree in law. Lustig’s primary objective is to understand how public health interventions can address the complex issues related to obesity and metabolic diseases. 

Lustig is the author of four influential books. His first book, Fat Chance, was published in 2012, followed by The Hacking of the American Mind in 2017. His third book, Metabolical in 2021, delves into the metabolic health concept, while his cookbook, The Fat Chance Cookbook, offers practical recipes for healthy eating. Currently, Lustig is working on a new book that explores the role of the amygdala, often misunderstood as the fear center of the brain, but which he argues is actually the decision-making center, and is at the root of our multiple health crises. 

Professor Lustig graciously agreed to share his insights on a range of topics, including the obesity crisis, childhood obesity, the low-fat diet debate, front-of-pack labeling, and various other scientific considerations.

The European Scientist : Obesity rates are worsening not only in America but worldwide. In your opinion, what are the factors causing this increase? Is this related to other populations adopting the American way of life?

Robert Lustig : This is a little complicated. Virtually everyone thinks this is about calories — calories in and calories out, gluttony and sloth. The first law of thermodynamics states that the total energy inside a closed system remains constant. However, there are two interpretations of this law. 

The standard interpretation is: “If you eat it, you better burn it, or you’re gonna store it.” In this view, weight gain results from an imbalance between eating and burning calories, implying that obesity is due to two behaviors: gluttony and sloth. This interpretation is pejorative, blaming the patient.

There’s another interpretation of the first law. If you are going to store energy, it is due to biochemical forces beyond your control that drive this process. This explains why states that increase energy burning, like consuming ephedrine or caffeine, make you feel good, while those that decrease it, like starvation or hypothyroidism, make you feel bad. If you are storing energy and need to burn it, you will have to eat it.

And now the two behaviors that we associate with obesity are secondary to a biochemical process that is the process of energy storage. The data show that the second interpretation is the correct one, not the first. As an endocrinologist who has done research in the field, I believe obesity is primarily due to a biochemical process.

To understand what this biochemical process is, that’s yet a bit more complicated. Almost assuredly insulin plays a major role in this. Our environment has become insulinogenic and obesogenic, with insulin levels today being two to four times higher than they were 40 years ago. 

Insulin is a prerequisite for energy storage. Insulin drives weight gain. Then the question is “what is driving the insulin?” And there, things are becoming even more complicated. There are  many changes in our environment that lead to the high insulin, and then the high insulin leads to the energy storage and then that energy storage leads to the increase in food intake. But they are all working on the phenomenon of energy storage. Of that I’m very sure. So what is the biggest of the things that lead to the energy storage and leads to insulin? I would have to say it is ultra-processed food. 

Basically, any country that adopts the Western diet suffers the same fate. However, even countries that have not adopted this diet have shown rising obesity rates. This raises the question: why? Two pieces of data are particularly relevant.

First, body temperature in the USA has decreased by 1.5 degrees Fahrenheit over the last 150 years, from 98.6 to 97.1. If you might wonder why your body temperature has fallen, why it would be consistent, and why it would occur in every demographic group—male, female, old, young—it doesn’t matter. Body heat is due to mitochondrial function: 40% of what you consume ends up as body heat. So, if you’re not consuming less, then your mitochondria must be working less well. So, what is making our mitochondria work less well?

Second, animals in captivity have gained weight consistently over the last 25 years, despite eating the same diets.

These two pieces of data suggest that there’s something in the environment that we and other animals are exposed to that is altering mitochondrial function, leading to energy storage instead of energy burning. Of this I am very sure that this is true.

TES.: As a specialist in childhood obesity, how do you explain the increasing prevalence of obesity among children? Should we blame genetics, or is the environment a more significant factor?

R.L.: First of all, we should not blame genetics. Genetics account for only 50% of obesity, with the environment making up the other 50%. Our genetics haven’t changed over the last 50 years, but our environment has. Known genetic polymorphisms related to obesity only explain about 10 kilos of weight, while we have a 20 to 30 kilo problem. Genetics alone cannot be the answer.

We now face an epidemic of obese newborns. They don’t diet or exercise, relying solely on what the mother provides through the placenta, which has changed over the past 50 years. Studies from the US, South Africa, Israel, and Russia show a trend of newborns gaining 200 grams (half a pound) over the last 25 years, all of it fat. This is due to epigenetics, not genetics. Epigenetics involves changes in gene expression, such as increased insulin production, without altering the DNA sequence.

I edited a book called Obesity Before Birth in 2010, exploring how our environment impacts our genes, which clearly plays a role.  It’s very Lamarckian, and that is also what Darwin describes as well. We often oppose them, but the fact is that they are both describing changes that have occurred due to changes in the environment. So, it is evident that changes in our environment have significantly contributed to these alterations.

My friend Bruce Blumberg at the University of California, Irvine studies how chemicals like tributyltin, found in plastics, lead to obesity. Tributyltin exposure affects the epigenetics of an enzyme that degrades insulin, leading to higher insulin levels. If a mother is exposed to tributyltin, her baby and subsequent generations can become fat, demonstrating epigenetic changes affecting four generations. So, this could be going on all over the world, all the time, due to factors that are out of individuals’ control. I am not a believer in the calorie hypothesis. I think that the calorie hypothesis is what has held this field back, and I’m doing my best to kill the calorie as a unit of measure because it just doesn’t make sense. 

It’s not the calories you eat, it’s the calories you absorb. For example, if you eat 160 calories of almonds, you absorb only 130 because the fiber in almonds forms a gel that prevents about 25% of the calories from being absorbed. So, the insoluble fiber, the cellulose in the almond, forms the fishnet , and the soluble fiber plugs the holes in that fishnet, and together they inhibit about 25% of the calories in the almond from ever reaching your bloodstream. Those calories travel down the intestine, where the microbiome consumes these unabsorbed calories, thus protecting the liver and feeding the gut. So, even if you ate 160 calories, you’ve only absorbed 130. So, a calorie is not a calorie if it comes with its associated fiber.

Another example is protein versus carbohydrates. Burning amino acids for energy requires removing the amino group, which costs energy. You end up with the same energy availability, but you have to expend energy to prepare the amino acid for processing. Therefore, there’s a net deficit compared to carbohydrates. So even though protein and carbohydrates both have four calories per gram, the amount of fat you will store is different. This is why a calorie is not just a calorie.

A final example is fructose and glucose—my favorite. Glucose is the energy of life. Every cell on the planet burns glucose for energy. Glucose is so important that if you don’t consume it, your body makes it. Fructose, however, is unnecessary for animal life and inhibits mitochondrial function by affecting an enzyme called AMP-kinase, rendering it dysfunctional—permanently dysfunctional. This inhibition may contribute to the decrease in body temperature. So, if you’re not burning energy, then you have only one choice: to store it. Therefore, we are consuming molecular toxins in every meal.

TES. : In the early 2000s, you were among the first to advocate against low-fat diets, presenting evidence that despite consuming fewer calories from fat, obesity rates continued to rise. Can you elaborate on this?

R.L.: Low fat means high sugar. Low fat tastes like cardboard, and the food industry had to do something to make the food palatable. So, when they took the fat out, they put the sugar in. The problem is that sugar, because it generates an increased insulin response and inhibits mitochondrial function, does double duty in terms of increasing weight gain. So, low-fat diets only work if you have a genetic defect in fat metabolism. That’s about one in 500 people. If you’re one of them, a heterozygote for familial hypercholesterolemia, you’ll probably need a low-fat diet. But the food industry was advocating a low-fat diet for the entire world based on a faulty premise. Why did they do that? Because it gave them a whole new set of products to sell. They took the fat from, say, milk and turned it into cheese. The cheese section in American stores used to be very small; now it is an entire aisle. It generated profit for the industry, and disease for us.

TES. : Your book “Sugar: The Bitter Truth” has been a worldwide bestseller. How do you explain its success?

R.L.: The short answer is, I don’t know. The long answer is that people have been told the wrong things for fifty years, and they’re starting to wake up. They’re beginning to realize that what they were told isn’t working. Maybe the reason it isn’t working is that it’s not true. I just happened to publish the book at a time when people were searching for other answers.

There’s a concept we carry around in our heads called the belief system. Here’s how I explain the belief system to people: If you’ve ever thought about changing religions, the fact is that your parents handed you a belief system when you were born. You grow up with that belief system, and if it starts to fail you, people don’t typically choose to change religions unless their belief system no longer explains the world in a way they understand.

Calories are its own belief system. Everyone was told that fat makes you fat, and the reason they were told this is that fat has nine calories per gram, while carbohydrates have four calories per gram. Since fat is more energy-dense, people assumed that eating fat would make you fat. That turns out to be completely untrue. The reason is that fat doesn’t stimulate insulin, while carbohydrates do. There is no weight gain without insulin. The fallacy was that calories dictated obesity, and people are waking up to the fact that this isn’t true. They needed an explanation that fit their belief system, so they had to change their belief system. I just happened to publish my book because I was doing research in the field at the right time, and that’s why it worked for people.

TES. : To combat poor nutrition, the EU is considering Front-of-Pack (FOP) labeling, with some advocating for the Nutri-Score system. What is your opinion on this solution, and what advice would you give to European policymakers?

R.L.: To be honest with you, the Nutri-Score system still leaves much to be desired, and I’ll explain why. The reason is that it’s not just about what’s in the food; it’s about what’s been done to the food. All food is inherently good; it’s what we do to the food that’s problematic. We have done four things to food that are particularly harmful: adding sugar, removing fiber, adding inflammatory fats (like Omega-6 and trans-fats) while removing anti-inflammatory fats (like Omega-3), and adding emulsifiers. Of these four factors, only the added sugar worsens the Nutri-Score label. Nutri-Score doesn’t account for the other three. So, I believe it’s not just what’s in the food, but what has been done to the food. I think explaining the degree of food processing to the public is more important than explaining what’s in the food. While Nutri-Score is an improvement over calorie counting, it’s not as good as explaining food processing. So, I have reservations.

TES. : Do you think the solution to poor nutrition lies in better food policy, or does it depend on individuals improving their dietary habits?

R.L.: I absolutely believe that we need changes in policy—without question. The reason is that no one can read the side of a food label effectively. No one knows how, no one knows why, and no one has time. Expecting people to make informed choices for themselves when they’re addicted to substances specifically added to food to make them buy more will not work. Personal responsibility alone is insufficient. Every issue of personal responsibility can become a public health crisis. HIV was considered a personal responsibility issue before it became a public health crisis. Teen pregnancy was a personal responsibility issue before it became a public health crisis. Tuberculosis, lead poisoning—when it becomes a public health crisis, you need a public health solution. And food is a public health crisis.

TES. : Would you say that nutrition is a science?

R.L.: Nutrition is a science, without a doubt. But here’s the problem: there are three terms that people often confuse as being the same, but they are not. These terms are food science, nutrition, and metabolic health. What are the differences?

Food science deals with what happens to the food between the ground and the mouth. Nutrition focuses on what happens to the food between the mouth and the cell. Metabolic health pertains to what happens inside the cell. All the diseases we are currently suffering from are diseases inside the cell. So, while nutrition can inform metabolic health, it is one step removed. Food science can also inform metabolic health, but it is two steps removed.

What you really need to focus on is metabolic health. In 2023, the World Economic Forum published a white paper called “The True Purpose of Nutrition,” which agreed that this purpose is metabolic health. If you don’t have metabolic health, then the rest of it doesn’t matter. People talk about saving the environment and addressing global warming, but if you don’t have metabolic health, you don’t have anything. So, you have to start there. That must be the North Star for any food system change—we have to improve metabolic health in the process. Nutrition doesn’t address this directly because it essentially involves adding up calories: what passes your lips, what gets absorbed, and how that impacts your metabolism are different phenomena.

For instance, sugar may be registered merely as calories, but if it’s damaging your AMP-kinase and impairing your mitochondria, how does that fit into the concept of nutrition? It is captured under metabolic health. To me, nutrition is a straw man; it is not the proper focus. Metabolic health is. Metabolic health is science, while nutrition is math. Dietitians can handle math, but only scientists can do science. Unfortunately, clinicians often lack this understanding as well.

TES. : What advice do you have for our readers?

R.L.: Three words: eat real food. In France, you are very fortunate to have access to wonderful real food. People often talk about the French paradox: how you can eat all these cheeses and still stay thin. The answer is that these are real foods. How do you know what is real food? Real food doesn’t have a label. It doesn’t need one, because nothing’s been done to it. When you see a food label, it’s a warning label. 

Image par fernando zhiminaicela de Pixabay

Books by Robert Lustig