I’ve been eating a high-fat, carb-restricted diet for almost 20 years, since I started as an experiment when investigating nutrition research for the journal Science. I find it’s easy for me to maintain a healthy weight when I eat this way. But even after two decades, the sensation of being on the edge of a slippery slope is ever-present.

The holidays and family vacations are a particular problem. Desserts and sweets will appear and I’m not good at saying no. The more sweets I eat, the more we eat as a family, the longer it takes upon returning home before that expectation of a daily treat fades away.

What I’ve realised is that eating a little of a dessert, pasta or bread fails to satisfy me. Rather it ignites a fierce craving for more. I find it easier to avoid sugar, grains and starches entirely, rather than to try to eat them in moderation. The question is why.

To begin to answer that question requires understanding that researchers are generally divided not only on what causes obesity, but also why we have cravings and often fail to stay on diets.

The conventional thinking is that obesity is caused by caloric excess. Researchers 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 self-discipline.

“It’s viewed as a psychological issue or even a question of character,” says David Ludwig, who studies and treats obesity at Harvard Medical School.

The minority position in this field — one that Dr Ludwig holds — 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, 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.

Why giving in to cravings leads to a food binge

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 Robert Lustig, a paediatric 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,” Dr Lustig 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 utilised — 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 centre 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.

Researchers believe that a person can minimise 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 behaviour,” Dr Ludwig says, “as opposed to high-carb foods which exacerbate it.”

Insulin levels are vital to understanding why we binge. Photo: ABC

Whatever the mechanism involved, if the goal is to avoid the kind of slip that leads from a forkful of rice to a doughnut binge, 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 also studies sugar.

The first strategy is to stay away from the trigger.

“Alcoholics who care about staying sober won’t get a job in a bar or even walk down the alcohol aisle in a grocery store,” says Dr Schmidt. “It’s harder to avoid junk foods in the food environment around us, but we can certainly clean up our home environment and avoid situations where sugar and other treats are easily available.”

Changing our social networks may be also necessary — convincing our families to be invested in eschewing these foods, just as they would help if we were trying to quit cigarettes, alcohol or drugs.

Another valuable technique is to learn to identify and avoid situations that weaken resolve or increase cravings.

“If I know that at 3pm I have a little slump and will want to go to the vending machine, then I can have food available that’s the equivalent but that won’t trigger a binge,” says Dr Schmidt.

− New York Times