Reviews | Carbohydrates, not calories, are responsible for obesity


David S.Ludwig is co-director of the New Balance Foundation Obesity Prevention Center at Boston Children’s Hospital, professor of pediatrics at Harvard Medical School, and professor of nutrition at Harvard TH Chan School of Public Health.

The usual way to understand obesity is simple: if you eat more calories than you need to eat, the excess gets deposited in body fat and you gain weight. Because, according to this approach, all calories look the same to the body, the only way to lose weight is to eat less or burn more through exercise.

For a century, this notion of “energy balance” has dominated the prevention and treatment of obesity, from the original emphasis on calorie counting in the early 1900s, to the low-fat diet (targeting the most energy-dense nutrient) of the late 1900s, to the recent emphasis on reducing consumption of modern processed foods high in fat and sugar.

If this theory is correct, however, it is difficult to square with the facts. After more than three decades of increases, calorie consumption in the United States has plateaued or declined since 2000, a new analysis finds. But obesity rates have risen by more than a third since then, reaching 42% of the population today. This paradox cannot be simply explained by our sedentary lifestyles – in fact, Americans have become quite a bit more physically active over the past 20 years.

What if the focus on calories and energy balance is just plain wrong, reversing cause and effect? Writing in the European Journal of Clinical Nutrition this week, my co-authors – researchers, doctors, public health experts – and I argue that overeating is not the primary cause of obesity. Instead, the weight gain process causes us to overeat.

This is a different model of obesity, the carbohydrate-insulin model. This theory blames the rise in obesity levels on the fast-digesting, processed carbohydrates that flooded our diets during the low-fat diet craze – white bread, white rice, prepared breakfast cereals, potato products and sweet foods. He postulates that consuming these carbs raises insulin levels too much and produces other hormonal changes that program our bodies to store additional fat.

Seen in this light, obesity is not a problem of overeating, it is a problem of calorie distribution – too many calories from each meal are siphoned off into fatty tissue and too few remain in the blood to satisfy the energy needs of the body. Therefore, our brain makes us feel hungrier sooner after eating to compensate for those sequestered calories. If we try to ignore hunger and limit calories, the body conserves energy by slowing down the metabolism. In this sense, obesity is a state of starvation in the midst of plenty.

According to this theory, simply cutting calories doesn’t work in the long run because it doesn’t address the underlying predisposition to store excess fat caused by hormones and other biological influences. Instead, the focus should be on reducing post-meal blood sugar and insulin spikes with a high-fat, low-processed carbohydrate diet. In this way, fatty tissue can be tricked into releasing pent-up calories, reducing hunger. Weight loss occurs without the need to restrict calories, which increases the chances of long-term success.

So, is the carbohydrate-insulin model more correct than the energy balance thinking? Unfortunately, we don’t know for sure yet. The definitive research needed to resolve this controversy has never been done, in part because alternative obesity paradigms have not been taken seriously.

Two scientific articles, in addition to the new one this week, aim to build the carbohydrate-insulin model from the available scientific evidence. Yet there have been more than a dozen papers from critics claiming to have refuted the model based on weak evidence, such as small, short-term trials of two weeks or less.

Meanwhile, despite investing in many major low-fat diet trials (virtually all showing no benefit for primary outcomes), the government’s National Institutes of Health has yet to fund a single long-term trial. low carb of a similar range. It was not a fair competition of ideas.

One of the reasons for this resistance could be cultural. For centuries, obesity has been considered a character flaw. Despite decades of research into the genetic and biological influences on body weight, obese people continue to be stigmatized, more than those with almost any other chronic disease, as if their weight is their fault.

Energy balance thinking implicitly contributes to these stereotypes by blaming overeating on poor self-control. Although newer versions of energy balance emphasize the primordial reward centers in the brain that determine food intake, in both cases obese people are considered unable to resist tempting foods for reasons conscious or unconscious. If the alternative paradigm is correct, however, then deeply ingrained notions about obesity are simply wrong.

Scientists are supposed to be skeptical. But when variations of the same approach continue to fail — and obesity rates continue to rise — it’s critical that new ideas are encouraged, not suppressed. And with the cost of just one weight-related complication, type 2 diabetes, nearly a billion dollars a day, we need to consider different ways to solve the intractable problem of obesity and open our minds to a notion radical: overeating is a symptom, not a cause.

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