How to Explain Obesity

The energy-balance model doesn’t help much

The carbohydrate-insulin model works better

For decades, researchers and health organizations have promoted the energy-balance model to account for obesity. It assumes that “a calorie is a calorie” in terms of weight gain and loss. According to the model, differing levels and types of carbohydrates, protein, and fats in foods don’t much matter, except insofar as the number of calories or the palatability of those foods are concerned. Weight gain is explained as excess calories consumed (especially fats) and insufficient energy expended, often reflected in a sedentary lifestyle. In other words, people who gain weight and get fat eat too many calories and don’t get enough exercise. This sensible-sounding model has two major limitations.

First, exhortations from medical authorities to eat fewer calories, less fat, and exercise more have been ineffective at preventing the large rise in obesity in the US and elsewhere over the past several decades. The prevalence of obesity increased while the number of calories we eat from fat decreased.

Second, persons with obesity are often stigmatized for their failure to exert sufficient will power over their eating or for some other psychological defect. Yet, research found minimal or no relationships between weight and measures of conscientiousness, agreeableness, emotional stability, or extraversion. Plus, it’s virtually impossible to estimate accurately how much we eat in a day within 350 calories.

David Ludwig, a nutrition researcher at Harvard, and colleagues summarized the carbohydrate-insulin model of obesity as a plausible and practical alternative to the energy balance model. The carbohydrate-insulin model reverses the direction of causality: Excessive deposition of dietary calories as fat leads to reduced satiety, increased hunger, and more eating. Overeating doesn’t make us fat; rather, the process of becoming fat makes us overeat. As the name “carbohydrate-insulin” model suggests, the key actors are carbs and insulin. Eating lots of carbs with high glycemic load (readily digestible and absorbable carbs, such as refined grains, potatoes, foods with lots of added sugar), leads to sharp rises in blood insulin. In response, muscles, liver, and fat cells rapidly take up food energy in the form of glucose. In addition, the liver and fat cells produce fatty acids. Several hours after a high-glycemic load meal, blood glucose drops to levels lower than those that existed prior to the meal, thereby stimulating hunger and eating.

A 2018 study by Ludwig and colleagues investigated diets with high (60), medium (40), and low (20 percent) carbohydrate, with protein content held constant. Total energy expenditure decreased by 52 calories per day for every 10 percentage point increase in carbohydrate content. Compared to the high-carbohydrate diet, total energy expenditure increased by 209 calories per day greater for participants on the low-carbohydrate diet. For participants with high, pre-project levels of insulin secretion, the differences in exergy expenditure were even greater: 308 calories per day greater total expenditure for participants with the low- versus high-carbohydrate diet. This study provides compelling evidence that calories are not necessarily interchangeable metabolically speaking.

Ironically, the demonization of fat over the past 50 years (as the prime culprit of obesity) led food manufacturers to increase the proportion of ultra-processed foods with high-glycemic load carbs, including sugar and white flour. Plus, ultra-processed foods comprise more than half of the average American’s food intake. According to the carbohydrate-insulin model, losing weight or maintaining weight loss is more a matter of what you eat rather than how much you eat. More specifically, emphasize foods with low-glycemic load.

Dariush Mozaffarian and colleagues at Tufts and Harvard used data from three long-term studies to determine which foods predicted long-term weight gain in men and women. Based on their results, you’re less likely to gain weight if you eat less white bread, other refined grain products (cookies, muffins, bagels), potatoes, and sugary beverages. To avoid gaining weight, emphasize yogurt (without added sugar), avocadoes, nuts, fruits, vegetables, seeds, and olive oil. Between 1971 and 2004, the average daily caloric intake for American women and men increased by 22 and 10 percent, respectively, mostly from refined carbohydrates, starches, and sugar-sweetened drinks. Rather than obsess about calories, shift your attention to foods that improve your health and help you avoid obesity.

No Comments Yet.

Leave a comment