The Complete Guide to Fasting

Distinguished as a Senior Fellow with Honors at Dartmouth College, Abel created his own curriculum to specialize in brain science, music, and technology. He later published his research in The Musical Brain, which became a number-one bestseller. (Location 457)

A therapeutic fast of 382 days was maintained with only a multivitamin with no harmful effects on health. In fact, this man felt terrific during this entire period. In a study of supervised fasts with only water and vitamins lasting up to 117 days, researchers confirmed that there were no changes in serum electrolytes, lipids, proteins, or amino acids. Moreover, they found that hunger was virtually absent during these prolonged fasts. Adrenaline Increases and Metabolism Speeds Up Most people expect that a period of fasting will leave them feeling tired and drained of energy. However, the vast majority of people experience the exact opposite: they feel energized and revitalized during fasting. Partly this is because the body is still being fueled—it’s just getting energy from burning fat rather than burning food. But it’s also because adrenaline is used to release stored glycogen and to facilitate fat-burning, even if blood sugar is high. The increased adrenaline levels invigorate us and stimulate the metabolism. In fact, studies show that after a four-day fast, resting energy expenditure increased by 12 percent. Rather than slowing the metabolism, fasting revs it up. Figure 1.4. Electrolytes remain stable during extended fasting. (Location 693)

Many of the effects of aging may result from low growth hormone levels. Replacing growth hormone in older people with low levels has significant anti-aging benefits. A randomized controlled study found that in men, six months of growth hormone replacement increased lean mass (bone and muscle) by an astounding 3.7 kilograms (8.2 pounds), even as fat mass decreased by 2.4 kilograms (5.3 pounds). Similar results were found in women. However, exogenous growth hormone—that is, growth hormone that isn’t made by your own body—carries the risk of unwanted side effects. (Location 715)

Meals very effectively suppress the secretion of growth hormone, so if we’re eating three meals per day, we get effectively no growth hormone during the day. Worse, overeating suppresses growth hormone levels by as much as 80 percent. (Location 722)

During fasting, in addition to the usual early-morning spike of growth hormone (pulsatile), there is also regular secretion throughout the day (non-pulsatile). Both pulsatile and non-pulsatile release of growth hormone is increased during fasting. Interestingly, very low-calorie diets are not able to provoke the same growth hormone response. (Location 724)