The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting

by Jason Fung

Animal studies show that fasting has remarkable promise as a therapeutic tool. Aging rats started on intermittent fasting regimens markedly improved their motor coordination, cognition, learning, and memory. Interestingly, there was even increased brain connectivity and new neuron growth from stem cells. A protein called brain-derived neurotrophic factor (BDNF), which supports the growth of neurons and is important for long-term memory, is believed to be responsible for some of these benefits. In animals, both fasting and exercise significantly increase the beneficial BDNF effects in several parts of the brain. Compared to normal mice, mice on an intermittent fasting regimen showed less age-related deterioration of neurons and fewer symptoms of Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease. Human studies on caloric reduction find similar neurologic benefits—and since fasting certainly restricts calories, this is one area where fasting and caloric reduction provide similar benefits. With a 30 percent reduction in calories consumed, memory significantly improved and the synaptic and electrical activity in the brain increased. In addition, insulin levels have an inverse correlation to memory—that is, the lower the insulin level, the more memory improves. On the flip side, a higher body mass index is linked to decline in mental abilities and decreased blood flow to those areas of the brain involved in attention, focus, reasoning, and more complex, abstract...