Have you heard of “intermittent fasting” as a way to loose weight and decrease the effects of aging? What is it? Is it just a fad, like so many other dietary/weight loss plans? Does it have some merit?
Intermittent fasting is time related fasting (going without eating or with reduced food intake for certain periods of time combined with eating regular meals at certain times). It is touted to have health benefits such as improving glucose regulation, increasing the body’s ability to deal with stress, suppressing inflammation (which is the basis of many chronic diseases), bringing about weight loss and better cardiovascular health, and decreasing cancer and neurodegenerative diseases.
The concept of intermittent fasting has its basis in decades of research, mainly on lab rodents, studying their behavior and longevity under different feeding conditions. It is more difficult to study dietary practices in humans than in laboratory animals, so the human studies generally have had small sample sizes, have been of relatively short duration (which makes it difficult to tell the outcomes of chronic diseases because they take a long time to develop), and often lack in control groups. However, the concept of intermittent fasting is presently undergoing a great deal of scientific scrutiny by respected researchers. In humans there is, though, a large and robust literature on shift workers, indicating that their disrupted sleep-wakefulness patterns as well as food intake during the night time hours leads to increased risk of obesity, diabetes, cardiovascular disease, and cancer (especially breast cancer).
We humans still have the genetics and metabolism we had 10,000 years ago as hunter-gatherers, when food sources were unreliable. Scientific thought is that our metabolism is geared to sustain us at times when food is not readily available. Fasting is probably evolutionarily embedded in our physiology. Humans also evolved to eat during the day-light hours and sleep at night. The time of day plays an important role in the integration of metabolism, energy, hormone secretion patterns, physical coordination, and sleep. Think circadian rhythm – our sleep-wakefulness patterns – which are dictated by the pineal gland in the center of the brain. Light is sensed by the retina in the back of the eye and these neural signals are sent to the visual areas of the brain. The chemical, melatonin, is secreted during dark hours and contributes to our sleep.
What happens during the switch from eating to fasting? It is thought that the fasting time allows the body to re-set pancreatic secretion of insulin along with other biochemical changes. After a 10 – 12 hour fast the body uses up its stores of glycogen (glucose ie, sugar) from the liver. The body then begins to derive its energy from fat cells, a process of metabolizing ketones. This switch to ketone metabolism stimulates something called “autophagy” by which the body is able to rid itself of damaged proteins decreasing the stress upon cells. The liver cannot use the ketones for energy, so they are released into the blood stream and used for energy in the peripheral tissues and the brain.
The two easiest methods of intermittent fasting are:
- 16-8 or 18-6 : meaning that there is time restricted eating, limited to daytime hours, either eating during 6 or 8 hours and fasting (except for water, black coffee, unsweetened tea) during 16 or 18 hours. For example, using the 16-8 system, one might have the first meal of the day at 9-10 AM and the last meal of the day at 4-5 PM with a fast till morning of the next day. This is probably the easiest system.
- 5:2 : meaning that one fasts two days per week by eating only 500-600 calories on fast days and eating regular meals on the other five days of the week, again with liquids limited to clear and unsweetened water, coffee, and tea and no snacking.
Nutritional advice if you decide to try intermittent fasting:
- It is vitally important to have a nutritionally strong diet during the times you are eating. Maintain an intake of high-quality food, concentrating on the most nutritious foods of colorful vegetables and fruits, beans and lentils, whole grains, adequate fluid intake, and no junk food.
- Be active to maintain muscle mass.
- Avoid sugar and “white stuff” (refined grains – white flour, white pasta, flour tortillas, white bread etc.).
- Let the body burn fat between meals. Don’t snack. No night time eating.
This style of eating is not recommended for: pregnant or nursing women, people who take medication to manage blood sugar, the already thin or elderly, people who have serious chronic diseases (unless approved by their physician), children, or people with a history of an eating disorder.
Intermittent fasting is probably the most scientifically researched dietary approach of all the “diets” presently available. That being said, definitive human studies have not yet been done. The best idea, if you are interested in this approach, is to keep up-to-date with information from well-established medical web sites such as the Mayo Clinic, WebMD, Harvard etc. A landmark review article was published in the New England Journal of Medicine, December 26, 2019 edition, entitled “Effects of Intermittent Fasting on Health, Aging, and Disease”, by Rafael de Cabo, Ph.D. and Mark Mattson, Ph.D., available on-line, for those interested in an in-depth scientific article.
