The conventional thinking, held by the large proportion of the many researchers and clinicians I’ve interviewed over the years, is that obesity is caused by caloric excess. They refer to it as an “energy balance” disorder, and so the treatment is to consume less energy (fewer calories) and expend more. When we fail to maintain this prescription, the implication is that we simply lack will power or self-discipline.
“It’s viewed as a psychological issue or even a question of character,” says Dr. David Ludwig, who studies and treats obesity at Harvard Medical School.
The minority position in this field — one that Dr. Ludwig holds, as do I after years of reporting — is that obesity is actually a hormonal regulatory disorder, and the hormone that dominates this process is insulin. It directly links what we eat to the accumulation of excess fat and that, in turn, is tied to the foods we crave and the hunger we experience. It’s been known since the 1960s that insulin signals fat cells to accumulate fat, while telling the other cells in our body to burn carbohydrates for fuel. By this thinking these carbohydrates are uniquely fattening.
Since insulin levels after meals are determined largely by the carbohydrates we eat — particularly easily digestible grains and starches, known as high glycemic index carbohydrates, as well as sugars like sucrose and high-fructose corn syrup — diets based on this approach specifically target these carbohydrates. If we don’t want to stay fat or get fatter, we don’t eat them.
This effect of insulin on fat and carbohydrate metabolism offers an explanation for why these same carbohydrates, as Dr. Ludwig says, are typically the foods we crave most; why a little “slip,” as addiction specialists would call it, could so easily lead to a binge.
Elevate insulin levels even a little, says Dr. Robert Lustig, a pediatric endocrinologist at the University of California, San Francisco, and the body switches over from burning fat for fuel to burning carbohydrates, by necessity.
“The more insulin you release, the more you crave carbs,” he said. “Once you’re exposed to a little carbohydrate, and you get an insulin rise from it, that forces energy into fat cells and that deprives your other cells of the energy they would otherwise have utilized — in essence, starvation. So you compensate by getting hungry, particularly for more carbohydrate. High insulin drives carb-craving.”
The result is that even a bite or a taste of carbohydrate-rich foods can stimulate insulin and create a hunger — a craving — for even more carbohydrates. “There’s no question in my mind,” says Dr. Lustig, “that once people who are ‘carboholics’ get their insulin levels down, they become less carboholic. And if they go off the wagon and start eating carbs, they go right back to where they were before. I’ve seen that in numerous patients.”
Sugar and sweets might be a particular problem because of several physiological responses that may be unique to sugar. Sugar cravings appear to be mediated through the brain reward center that is triggered by other addictive substances. Both sugar and addictive substances stimulate the release of a neurotransmitter called dopamine, producing an intensely pleasurable sensation that our brains crave to repeat. Whether this really is a significant player in sugar cravings is one of many areas of controversy in the field.
Researchers like Dr. Ludwig and Dr. Lustig who also see patients, and physicians, nutritionists and dietitians who promote carb-restricted diets, believe that a person can minimize these carbohydrate cravings by eating lots of healthful fats instead. Fat is satiating, says Dr. Ludwig, and it’s the one macronutrient that doesn’t stimulate insulin secretion. Eating fat-rich foods, “helps extinguish binge behavior,” Dr. Ludwig says, “as opposed to high-carb foods which exacerbate it.” (Although the definition of a “healthful” fat is another topic of debate.)
Whatever the mechanism involved, if the goal is to avoid the kind of slip that leads from a single forkful of rice to a doughnut binge or falling off your diet for good, then the same techniques that have been pioneered in the field of drug addiction for avoiding relapses also should work in this scenario as well. These basic principles have been developed over decades, says Laura Schmidt, an addiction specialist at the University of California, San Francisco School of Medicine who now studies sugar as well. They can “work for anyone who’s gotten clean and sober and wants to stay that way.”
Author: Gary Taub