Obesity, weight loss conventional wisdom may be wrong

For the past century, people wanting to lose weight have been advised to “eat less” and “move more.” Americans have actually gotten a little better at doing this over the past 20 years—calorie consumption has plateaued or declined and physical activity has modestly increased—but obesity rates have increased by one-third to 42% of the population. Researchers are now arguing that this is because the current “energy balance” approach to understanding weight gain may be wrong.

Overeating isn’t the primary cause of weight gain, according to David Ludwig, professor in the Department of Nutrition at Harvard T.H. Chan School of Public Health. “Instead, the process of gaining weight causes us to overeat,” he wrote in a July 28, 2022 Washington Post opinion piece.

This theory, called the “carbohydrate-insulin model,” blames obesity on processed, fast-digesting carbohydrates found in foods like french fries and sugary breakfast cereals. After consuming these foods, the resulting surge of blood glucose and insulin causes the body to send too many calories into fat tissue, leaving too few in the bloodstream to satisfy energy needs. As a result, the brain quickly sends the body messages of hunger again. If a person tries to ignore this hunger and restrict calories, their body responds by slowing the metabolism to conserve energy.

In a paper published July 28 in the European Journal of Clinical Nutrition, Ludwig and co-authors including Walter Willett, professor of epidemiology and nutrition, outline the current research around the carbohydrate-insulin model and rebut arguments against it.

More research is needed to test this theory, Ludwig wrote in the Post. If the model is correct, then it would show that deeply ingrained ideas about obesity—especially the stereotype that weight gain is due to poor self-control—are simply wrong.

Read the Washington Post opinion piece: What if the focus on calories and energy balance is simply wrong?

Learn more

A new framework for understanding obesity (Harvard Chan School news)