If you have not read Dr. Fung's 'Obesity Code', I highly recommend it. Here are a few excerpts and broad strokes.
"THERE ARE TWO prominent findings from all the dietary studies done over the years. First: all diets work. Second: all diets fail."
"The dreaded plateau, then weight regain, followed."
"Permanent weight loss is actually a two-step process. There is a short-term and a long-term (or time-dependent) problem."
"The hypothalamic region of the brain determines the body set weight"
"In the short term, we can use various diets to bring our actual body weight down. However, once it falls below the body set weight, the body activates mechanisms to regain that weight—and that’s the long-term problem."
"Insulin acts here to set body set weight higher. In the short term, we can use various diets to bring our actual body weight down. However, once it falls below the body set weight, the body activates mechanisms to regain that weight—and that’s the long-term problem."
"There is no one single cause of obesity. Do calories cause obesity? Yes, partially. Do carbohydrates cause obesity? Yes, partially. Does fiber protect us from obesity? Yes, partially. Does insulin resistance cause obesity? Yes, partially. Does sugar cause obesity? Yes, partially. All these factors converge on several hormonal pathways that lead to weight gain, and insulin is the most important of these. Low-carbohydrate diets reduce insulin. Low-calorie diets restrict all foods and therefore reduce insulin. Paleo and LCHF diets (low in refined and processed foods) reduce insulin. Cabbage-soup diets reduce insulin. Reduced-food-reward diets reduce insulin."
"Too often, our current model of obesity assumes that there is only one single true cause, and that all others are pretenders to the throne. Endless debates ensue. Too many calories cause obesity. No, too many carbohydrates. No, too much saturated fat. No, too much red meat. No, too much processed foods. No, too much high fat dairy. No, too much wheat. No, too much sugar. No, too much highly palatable foods. No, too much eating out. It goes on and on. They are all partially correct."
"...tailor the approach individually to address the cause of the high insulin levels. For example, if chronic sleep deprivation is the main problem causing weight gain, then decreasing refined grains is not likely to help. If excessive sugar intake is the problem, then mindfulness meditation is not going to be especially useful. Obesity is a hormonal disorder of fat regulation. Insulin is the major hormone that drives weight gain, so the rational therapy is to lower insulin levels."
"Long-term weight loss is really a two-step process. Two major factors maintain our insulin at a high level. The first is the foods that we eat—which are what we usually change when we go on a diet. But we fail to address the other factor: the long-term problem of insulin resistance. This problem is one of meal timing."