The Carbohydrate-Insulin Model: Is It Too Simple?

According to Kevin Hall, PhD, a senior investigator at the Laboratory of Biological Modeling at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) at the National Institutes of Health (NIH) in Bethesda, Maryland, at best, the carbohydrate-insulin model is too simple, while at worst, it is simply false. He noted that differences in body fat and energy expenditure often occur in directions diametrically opposed to the presumed effects of insulin. The minimal long-term differences in mean weight loss in controlled trials comparing low-carb with low-fat diets suggest little generalizable effect on hunger and appetite.

“The carbohydrate-insulin model of obesity theorizes that diets high in carbohydrate are particularly fattening due to their propensity to elevate insulin secretion, which promotes storage of fat in adipose tissue and directs circulating fat away from being burned by metabolically active tissues,” said Dr Hall. However, he explained that this has been investigated and has not panned out. It is suggested that diets high in carbohydrates result in a perceived state of cellular “internal starvation” and a consequent slowing of metabolism. He said hunger and appetite are purported to increase, thereby promoting the positive energy balance associated with the development of obesity.

However, several logical consequences of the carbohydrate-insulin model of obesity were recently investigated and they showed these assumptions are incorrect, according to Dr Hall. “The studies failed to support key model predictions regarding energy expenditure and body fat. Therefore, important aspects of the carbohydrate-insulin model have been experimentally falsified, suggesting that the model is too simplistic.”

He said that he agrees with many of the critics of the “calories in, calories out” paradigm of obesity and its treatment, noting that this approach leads to clinicians simply telling patients to take responsibility and eat less and exercise more.  

“Failure to lose substantial amounts of weight through modest prescribed lifestyle changes has been erroneously attributed to lack of willpower. Such ideas promote weight bias and are factually incorrect because they fail to account for the fact that body weight is regulated as part of a complex neuroendocrine feedback-control system,” said Dr Hall.

Nevertheless, he noted that the idea that there is a special combined proportion of dietary macronutrients that translates to a generalizable advantage for long-term weight loss in most patients does not appear to be supported by any of the currently published data.

Exercise Matters

Barry Braun, PhD, professor and department head and executive director of the Human Performance Clinical/Research Laboratory College of Health and Human Sciences at Colorado State University in Fort Collins, said exercise can play a key role in a diet plan designed for weight loss. It helps to induce a caloric deficit as well as preserve muscle mass and minimize the decline in resting metabolic rate.