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It’s not overeating, but what we eat, that causes weight gain

The traditional energy-balance model teaches us that the maintenance of body weight is achieved by balancing the calories we consume with the energy we expend. This philosophy underlies the USDA’s Dietary Guidelines for Americans 2020-2025 which state that losing weight requires adults to reduce the number of calories they get from foods and beverages and increase the amount expended through physical activity.

According to this approach, losing weight should be a simple matter of reducing the amount we eat and increasing the extent of physical activity. Despite decades of public health warnings, however, levels of obesity continue to rise.  

The Centers for Disease Control and Prevention state that more than 40 percent of adult Americans are currently affected by obesity, despite the apparently simple solution proposed by the energy-balance model.   

The authors of a recent study from the American Society for Nutrition propose that a different model, the carbohydrate-insulin model, better explains the metabolic origins of weight gain and obesity. This model is not new – ir was developed in the early 1900s – but the recent study summarizes the current scientific evidence that supports it. The research is authored by 17 internationally recognized scientists, public health experts and clinical researchers. 

According to lead author Dr. David Ludwig, an endocrinologist at Boston Children’s Hospital and professor at Harvard Medical School, the energy-balance model doesn’t help us understand the biological causes of weight gain. “During a growth spurt, for instance, adolescents may increase food intake by 1,000 calories a day. But does their overeating cause the growth spurt or does the growth spurt cause the adolescent to get hungry and overeat?”

In contrast to the “calorie in, calorie out” approach of the energy-balance model, the carbohydrate-insulin model proposes that obesity is not caused by overeating but rather by the quality of the food we eat. In particular, our modern diets that contain a high glycemic load are to blame for the obesity pandemic. Glycemic load is a measure of the amount that a food will raise the blood sugar level after it is eaten. Foods that have a high glycemic load include those with high levels of easily digestible refined starch and sugar. 

According to the carbohydrate-insulin model, the consumption of foods with a high glycemic load leads to an increase in the secretion of insulin, a hormone that normally helps remove sugar from the blood and store it in liver and muscle cells. In the case of high levels of insulin, however, the fat cells are stimulated to increase their storage of calories, leading to enhanced deposition of body fat. This also leaves lower levels of sugar in the blood and leads to feelings of hunger. Ironically, the body may feel it is starved of energy and respond by slowing down the metabolic rate. 

Acceptance of the carbohydrate-insulin model necessitates a whole new way of approaching the management of weight and the treatment of obesity. Instead of limiting calorie intake or increasing energy expenditure, strategies that have not been particularly successful in the past, we should focus on what we eat and on how specific foods affect our hormone levels and metabolism. 

“Reducing consumption of the rapidly digestible carbohydrates that flooded the food supply during the low-fat diet era lessens the underlying drive to store body fat,” said Dr. Ludwig. “As a result, people may lose weight with less hunger and struggle.” 

Foods with high glycemic loads should be replaced with non-starchy vegetables, legumes, whole fruits and intact whole grains, all of which tend to have a moderate or low glycemic load.

The study is published in The American Journal of Clinical Nutrition.

By Alison Bosman, Staff Writer

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