Intermittent fasting is not a diet, it is an eating pattern; while a diet prescribes what one can eat, intermittent fasting prescribes when one can eat. The goal of intermittent fasting is to increase the time between dinner and breakfast. The first food or drink you consume during the day breaks your nightly fast. Our bodies run on cycles, and the first thing you put into your body that isn’t water — anything that needs to be metabolized — sets off a roughly 12-hour cycle of hormones and metabolic enzymes that promote proper digestion. Eating outside of this window without the help of metabolic enzymes increases fat production and decreases insulin sensitivity, which makes you crave more calorie-dense food, like pasta and fries, and deteriorates muscle mass. Conversely, eating within a window of fewer than 12 hours increases muscle mass and improves endurance (Satchin Panda, Ph.D.).
Many people may be drawn to intermittent fasting (IF) because of its weight-loss effects. However, several studies have concluded that weight loss, specifically fat reduction, is only a symptom of other profound physical benefits (Canadian Medical Association Journal). According to Mark Mattson, senior investigator for the National Institute on Aging, when cells are in a period of fasting, they are experiencing a stressor. Counterintuitively, mild environmental stressors such as this are good because cells “respond to the stress adaptively by enhancing their ability to cope with stress and, maybe, to resist disease.” Mattson continued that “there is considerable similarity between how cells respond to the stress of exercise and how cells respond to intermittent fasting.”
Studies with mice have demonstrated that intermittent fasting doesn’t just foster weight loss through fat, but also increases lean muscle mass by roughly 13 percent without any extra exercise or change in diet by increasing levels of growth hormones (Endocrinology). Mice who are IF have also been seen to “improve metabolic homeostasis through adipose thermogenesis” (Cell Research). Adipose thermogenesis is when adipose tissue, otherwise known as fat, gets metabolized by the body and burned to create heat energy. Apart from burning fat and increasing muscle mass, IF also may promote gut bacteria diversity and richness.
IF has psychological benefits as well. Multiple studies have found an increase in the protection of memory and “learning functionality” while following IF (Canadian Medical Association Journal). IF also increases insulin sensitivity by dropping insulin to lower levels during your fasting period. Insulin is a hormone that facilitates the process of storing fat in the body and acts as an appetite stimulant. Every time you eat, your body releases insulin to store the energy you are putting in your body, but insulin has to drop to a low level to release the hormone glucagon, which retrieves and uses energy stored by insulin. If one were to eat roughly every two hours, insulin levels would never drop low enough to release glucagon, meaning energy stored in cells would constantly accumulate and never get used (PubMed). Psychologically, this means that if you go roughly four hours after eating a meal without spiking your insulin again via snack, your body will start running on the glucagon-provided stored energy and you will become less hungry.
Short periods of fasting are beneficial, but even longer fasts have greater effects. When mice fast for a 16-hour period, for example, their levels of norepinephrine in the brain increase by roughly 60 percent. This makes sense because norepinephrine is a concentration and focus neurotransmitter. After 16 hours of no food, the brain has a greatly increased need to focus, so norepinephrineevolutionarily helping a creature find food more efficiently (Endocrinology).
One final potential psychological benefit of IF demonstrated in mice is its ability to decrease anxiety. After a 16-hour fast, mice showed diminished long-term memory of frightful events. This is probably the strangest symptom of IF, illustrating that IF’s mental and physical benefits may span a broad range.
Fasting can be a dangerous practice if done incorrectly, and these effects by no means indicate that everyone should start fasting themselves. However, research shows that eating within a smaller window of time does promote healthy weight management, individuals must determine the right balance of when to eat and what to eat.