Although there have been a number of recent studies assessing the effects of intermittent fasting on people, none are long term, and the vast majority of disease-related findings stem from research on laboratory animals. For example, in an animal model of stroke, those fed only intermittently suffered less brain damage because they were better able to resist the stress of oxygen and energy deprivation.
Other animal studies have shown a “robust disease-modifying” benefit of intermittent fasting on “a wide range of chronic disorders, including obesity, diabetes, cardiovascular disease, cancers and neurodegenerative brain diseases,” the researchers reported. Their review of both animal and human studies found improvements in a variety of health indicators and a slowing or reversing of aging and disease processes.
For example, human studies of intermittent fasting found that it improved such disease indicators as insulin resistance, blood fat abnormalities, high blood pressure and inflammation, even independently of weight loss. In patients with multiple sclerosis, intermittent fasting reduced symptoms in just two months, a research team in Baltimore reported in 2018.
If you think evolutionarily, Dr. Mattson said, predators in the wild fight for prey in the fasting state and are better at recovering from inevitable injuries. The human counterpart — people who evolved in feast-or-famine environments — would not have survived unless somehow protected by fasting.
“Our human ancestors did not consume three regularly spaced large meals, plus snacks, every day, nor did they live a sedentary life,” the researchers wrote. The studies they analyzed showed that “most if not all organ systems respond to intermittent fasting in ways that enable the organism to tolerate or overcome the challenge” and then return to normal.
Dr. Mattson explained that during a fast, the body produces few new proteins, prompting cells to take protein from nonessential sources, break them down and use the amino acids to make new proteins that are essential for survival. Then, after eating, a lot of new proteins are produced in the brain and elsewhere.
A reasonable question might be “How safe is intermittent fasting?” When fats are used for energy, they produce substances called ketone bodies that “regulate the expression and activity of many proteins and molecules that are known to influence health and aging,” the researchers reported. Ketosis, a build-up of acidic ketones in the blood, is a state that the Atkins diet, the ketogenic diet and other carbohydrate-restricted diets aim to achieve. Taken to extremes, however, ketosis can damage the liver, kidneys and brain and is especially dangerous to people with various chronic disorders like diabetes and heart disease.