..factors in the environment have triggered fat cells in our bodies to take in and store excessive amounts of glucose and other calorie-rich compounds. Since fewer calories are available to fuel metabolism, the brain tells the body to increase calorie intake (we feel hungry) and save energy (our metabolism slows down). Eating more solves this problem temporarily but also accelerates weight gain. Cutting calories reverses the weight gain for a short while, making us think we have control over our body weight, but predictably increases hunger and slows metabolism even more.
..In a sense, the conventional view of obesity as a problem of calorie balance is like conceptualizing fever as a problem of heat balance; technically not wrong, but not very helpful, because it ignores the apparent underlying biological driver of weight gain.
..As it turns out, many biological factors affect the storage of calories in fat cells, including genetics, levels of physical activity, sleep and stress. But one has an indisputably dominant role: the hormone insulin. We know that excess insulin treatment for diabetes causes weight gain, and insulin deficiency causes weight loss. And of everything we eat, highly refined and rapidly digestible carbohydrates produce the most insulin.
By this way of thinking, the increasing amount and processing of carbohydrates in the American diet has increased insulin levels, put fat cells into storage overdrive and elicited obesity-promoting biological responses in a large number of people.