The Obesity Code: Unlocking the Secrets of Weight Loss (Why Intermittent Fasting Is the Key to Controlling Your Weight)

by Jason Fung

Insulin is a key regulator of energy metabolism, and it is one of the fundamental hormones that promote fat accumulation and storage. Insulin facilitates the uptake of glucose into cells for energy. Without sufficient insulin, glucose builds up in the bloodstream. Type 1 diabetes results from the autoimmune destruction of the insulin-producing cells in the pancreas, which results in extremely low levels of insulin.

Insulin is a storage hormone. Ample intake of food leads to insulin release. Insulin then turns on storage of sugar and fat. When there is no intake of food, insulin levels fall, and burning of sugar and fat is turned on. This process happens every day. Normally,

The key to understanding obesity is to understand what regulates body set weight, why body set weight is set so high, and how to reset it lower.

I CAN make anybody fat. How? By prescribing insulin. It won’t matter that you have willpower, or that you exercise. It won’t matter what you choose to eat. You will get fat. It’s simply a matter of enough insulin and enough time. High insulin secretion has long been associated with obesity:1 obese people secrete much higher levels of insulin than do those of normal weight. Also, in lean subjects, insulin levels quickly return to baseline after a meal, but in the obese, these levels remain elevated. Insulin levels are almost 20 percent higher in obese subjects,2 and these elevated levels are strongly correlated to important indices such as waist circumference and waist/hip ratio.

Drugs that raise insulin levels cause weight gain. Drugs that have no effect on insulin levels are weight neutral. Drugs that lower insulin levels cause weight loss. The effect on weight is independent of the effect on blood sugar. A recent study29 suggests that 75 percent of the weight-loss response in obesity is predicted by insulin levels. Not willpower. Not caloric intake. Not peer support or peer pressure. Not exercise. Just insulin.

The question is not how to balance calories; the question is how to balance our hormones. The most crucial question in obesity is how to reduce insulin.

With short-term physical stress, insulin and cortisol play opposite roles. Something quite different happens, though, when we’re under longterm psychological stress.

Patients gain weight no matter how little they eat and no matter how much they exercise. Any disease that causes excess cortisol secretion results in weight gain. Cortisol causes weight gain. However, there’s evidence of the association between cortisol and weight gain even in people who don’t have Cushing’s syndrome. In a random sample from north Glasgow, Scotland,15 cortisol-excretion rates were strongly correlated to body mass index and waist measurements. Higher cortisol levels were seen in heavier people. Cortisol-related weight gain, particularly abdominal fat deposits, results in an increased waist-to-hip ratio. (This effect is significant because abdominal fat deposits are more dangerous to health than all-over weight gain.)

Population studies consistently link short sleep duration and excess weight,24, 25 generally with seven hours being the point where weight gain starts. Sleeping five to six hours was associated with a more than 50 percent increased risk of weight gain.26 The more sleep deprivation, the more weight gained.

SLEEP DEPRIVATION IS a potent psychological stressor and thus stimulates cortisol. This, in turn, results in both high insulin levels and insulin resistance. A single night of sleep deprivation increases cortisol levels by more than 100 percent.27 By the next evening, cortisol is still 37 percent to 45 percent higher.28

In the case of insulin resistance, it comes down to both meal composition and meal timing—the two critical components of insulin resistance. The types of food eaten influence the insulin levels. Should we eat candy or olive oil? This is the question of macronutrient composition, or “what to eat.” However, the persistence of insulin plays a key role in the development of insulin resistance, so there is also the question of meal timing, or “when to eat.” Both components are equally important. Unfortunately, we spend obsessive amounts of time and energy trying to understand what we should be eating and devote virtually no time to when we should be eating. We are only seeing half the picture.