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

by Jason Fung

Fat is simply the body’s stored food energy. In times of food scarcity, stored food (fat) is naturally released to fill the void. The body does not “burn muscle” in an effort to feed itself until all the fat stores are used.

Regular fasting, by routinely lowering insulin levels, has been shown to significantly improve insulin sensitivity.8 This finding is the missing piece in the weight-loss puzzle. Most diets restrict the intake of foods that cause increased insulin secretion, but don’t address insulin resistance. You lose weight initially, but insulin resistance keeps your insulin levels and body set weight high. By fasting, you can efficiently reduce your body’s insulin resistance, since it requires both persistent and high levels.

Adrenalin Fasting increases adrenalin levels, starting at around twenty-four hours. Forty-eight hours of fasting produces a 3.6 percent increase in metabolic rate,15 not the dreaded metabolic shutdown so often seen in caloric-reduction strategies. In response to a four-day fast,16 resting energy expenditure increased up to 14 percent. Rather than slowing metabolism, the body revs it up instead. Presumably, it does this so we have energy to go out and find more food.

Many people worry that fasting may cause malnutrition, but this concern is misplaced. The body’s fat stores are, for most of us, quite ample for our bodies’ needs. Even studies of prolonged fasting have found no evidence of malnutrition or micronutrient deficiency. Potassium levels may decrease slightly, but even two months of continuous fasting did not decrease levels below normal, even without the use of supplements.11 Note that this duration of fasting is far longer than is generally recommended without medical supervision. Magnesium, calcium and phosphorus levels during fasting are stable12—presumably, because of the large stores of these minerals in the bones. Ninety-nine percent of the body’s calcium and phosphorus is stored in the bones. A multivitamin supplement will provide the recommended daily allowance of micronutrients. In one case, a therapeutic fast of 382 days was maintained with only a multivitamin, with no harmful effect on the subject’s health. Actually, this man maintained that he felt terrific during the entire period.13 There were no episodes of hypoglycemia, as blood sugars were maintained within the normal range. The only concern may be a slight elevation in uric acid, which has been described in fasting.14

Starvation mode, as it is popularly known, is the mysterious bogeyman always raised to scare us away from missing even a single meal. This is simply absurd. Breakdown of muscle tissue happens only at extremely low levels of body fat—approximately 4 percent—which is not something most people need to worry about. At this point, there is no further body fat to be mobilized for energy, and lean tissue is consumed. The human body has evolved to survive episodic periods of starvation. Fat is stored energy and muscle is functional tissue. Fat is burned first. This situation is akin to storing a huge amount of firewood but deciding to burn your sofa instead. It’s stupid. Why do we assume the human body is so stupid? The body preserves muscle mass until fat stores become so low that it has no other choice.

Food is a celebration of life. Every single culture in the world celebrates with large feasts. That’s normal, and it’s good. However, religion has always reminded us that we must balance our feasting with periods of fasting—“atonement,” “repentance” or “cleansing.” These ideas are ancient and time-tested. Should you eat lots of food on your birthday? Absolutely. Should you eat lots of food at a wedding? Absolutely. These are times to celebrate and indulge. But there is also a time to fast. We cannot change this cycle of life. We cannot feast all the time. We cannot fast all the time. It won’t work. It doesn’t work.

Eating continuously is a recipe for weight gain. Intermittent fasting is a very effective way to deal with when to eat. In the end, the question is this: If you don’t eat, will you lose weight? Yes, of course. So there is no real doubt about its efficacy. It will work.