The authors of a new opinion article in the American Journal of Clinical Nutrition claim that overeating should not be treated as the principal cause of obesity today.
Statistics from the American CDC reveal that obesity affects more than 40% of American adults, placing them at higher risk for heart disease, stroke, type 2 diabetes, and certain types of cancer.
The standard advice for combatting obesity, including in the USDA’s Dietary Guidelines for Americans 2020-2025, are as you might expect, 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.”
But if the authors of this new piece are right, and preventing overeating isn’t the best way to combat obesity – what is?
It’s not overeating: a new perspective on obesity
The dominant model, that overeating leads to obesity, makes sense intuitively, and it fits the modern food environment well. In a world of hyper-palatable, seductively marketed food, it’s easy to consume far more calories than you need on a daily basis, which would explain why so many people are overweight.
But the authors of “The Carbohydrate-Insulin Model: A Physiological Perspective on the Obesity Pandemic,” an opinion published in The American Journal of Clinical Nutrition, point to fundamental problems with the calories-in-calories-out model, and argue that an alternative, which they call the carbohydrate-insulin model, better explains obesity and weight gain.
In addition, they claim that the carbohydrate-insulin model suggests more effective treatments for being overweight than the traditional focus on overeating.
Lead author Dr. David Ludwig, Endocrinologist at Boston Children’s Hospital and Professor at Harvard Medical School, points out that the calories-in-calories-model doesn’t get us very far when we’re trying to understand the biological causes of weight gain. He says,
“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?”
Instead of placing the emphasis on overeating as the cause of obesity, the alternative carbohydrate-insulin model focuses on modern dietary patterns characterized by excessive consumption of foods with a high glycemic load.
In particular, the authors mean processed, rapidly digestible carbohydrates – processed food, in short, which we have already called “a food that makes you ugly”, with good reason. Processed foods drive hormonal responses that fundamentally change our metabolism, driving fat storage, weight gain, and obesity.
Processed food: a shocking case study
Recently we reported on the case of a doctor who, as part of a BBC documentary ate a diet consisting of 80% ultra-processed food for a month. As well as experiencing weight gain, anxiety, loss of libido and piles, brain scans revealed that his brain had been quite literally “rewired” in a manner characteristic of drug addicts! The image below is taken from a MailOnline article about the doctor’s self-experiment and details the changes to his brain in depth. Scary.
When we eat such highly processed carbohydrates, the body secretes more insulin and suppresses secretion of another hormone called glucagon. In turn, this sends signals to fat cells to store more calories, leaving fewer calories available to fuel muscles and other metabolically active tissues.
The brain perceives that the body isn’t getting enough energy, which, in turn, leads to feelings of hunger, which then leads to overeating. In addition, metabolism may slow down in the body’s attempt to conserve fuel. Thus, we tend to remain hungry, even as we continue to gain excess fat.
The authors claim, then, that to understand the obesity epidemic, we need to consider not only whether we’re overeating, but also how the foods we eat affect our hormones and metabolism. Crucially, they claim, the calories-in-calories-out model misses that not all foods are created equal. A calorie is not a just a calorie.
Although the carbohydrate-insulin model is not new, this new formulation is the most comprehensive so far, featuring the input of a team of 17 prominent scientists, clinical researchers, and public health experts.
The authors state that further research is necessary, and to that end they have put forward a number of testable hypotheses to guide future research. These hypotheses will allow researchers to see which model, traditional or new, fits the evidence best.
As we said earlier, adoption of the carbohydrate-insulin model has potentially radical implications for the treatment of obesity in the future. Rather than urging people to avoid overeating, the new model suggests instead a focus on what we eat.
According to Dr. Ludwig, “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. As a result, people may lose weight with less hunger and struggle.”
