Intermittent fasting and its effects on the body and brain

Intermittent fasting has rapidly gained followers in the medical profession and public arena, but why and how does it work?

It’s tempting to think you can eat your way to good health – swap out those bad foods for heavily promoted “superfoods” and you’ll be well on your way to living forever. The science is increasingly pointing in another direction, to fasting rather than eating different foods, as the path to better health, although most studies on fasting have been conducted on animals, not humans.

Fasting has been shown to improve biomarkers (the biological signs) of disease, reduce oxidative stress (when levels of antioxidants in our body are not high enough to counteract the damage caused by free radicals) and preserve learning and memory functioning, according to Mark Mattson, senior investigator for the National Institute on Aging, part of the US National Institutes of Health.

There are several theories about why fasting provides physiological benefits, says Mattson. “The one that we’ve studied a lot, and designed experiments to test, is the hypothesis that during the fasting period, cells are under a mild stress,” he says. “And they respond to the stress adaptively by enhancing their ability to cope with stress and, maybe, to resist disease.”

In another study, Mattson and colleagues explored the effects of intermittent and continuous energy restriction on weight loss and various biomarkers (for conditions including breast cancer, diabetes and cardiovascular disease) among young overweight women. They found that intermittent restriction was as effective as continuous restriction for improving weight loss, insulin sensitivity and other health biomarkers.

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Mattson has also researched the protective benefits of fasting to neurons. If you don’t eat for 10 to 16 hours, your body will go to its fat stores for energy, and fatty acids called ketones will be released into the bloodstream. This has been shown to protect memory in brain and learning functions, says Mattson, as well as slow disease processes in the brain.

When you go without food for a short time, your body diverts its energy away from digesting food to cellular repair and the removal of waste material and toxins,
a process known as autophagy.

​Dr Colin Champ, assistant professor at the University of Pittsburgh Medical Centre, explains it like this: “Think of it as our body’s innate recycling programme. Autophagy makes us more efficient machines to get rid of faulty parts, stop cancerous growths and stop metabolic dysfunction like obesity and diabetes.”

By boosting your body’s autophagy process through intermittent fasting you dampen inflammation, enhance biological function and slow down the aging process. Intermittent fasting also results in a phenomenon known as apoptosis whereby the body rids itself of old, unhealthy cells, and replaces them with new ones. Researchers have noted that several genes related to longevity and protection against disease are automatically switched on when your body enters a fasting state.


Intermittent fasting is an umbrella term for diets that cycle between a period of fasting and non-fasting during a defined period. It can be grouped into two categories: whole-day fasting and time-restricted feeding.

Whole-day fasting involves regular one-day fasts. The strictest form is alternate-day fasting. This involves a 24-hour fast followed by a 24-hour non-fasting period. The well-known 5:2 diet allows the consumption of 500-600 calories on two fasting days in a seven-day cycle.

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Time-restricted feeding, on the other hand, involves eating only during a certain number of hours each day. A common form involves fasting for 16 hours each day and only eating during the remaining eight hours, typically on the same schedule each day. A more liberal practice would be 12 hours of fasting and a 12-hour eating window, or a stricter form would be to eat one meal per day, which would involve around 23 hours of fasting per day.



Short-term fasting has been found to increase neural autophagy, which is how cells regenerate, repair themselves and recycle waste. This equals a boost in memory, and brain and learning functions.

Studies on rodents have shown that during the fasting period, cells are put under minor stress to which they react by enhancing their ability to cope with stress. This could help resistance to diseases such as Parkinson’s, Alzheimer’s, heart disease, cancer, asthma, epileptic seizures, diabetes and strokes.

The University of Illinois studied the effects of alternate-day fasting on hundreds of obese adults. An 8-10 week trial found participants lost an average of 5.8kg and had marked reductions in cholesterol, blood pressure and insulin, the fat-storage hormone.

While the reduction in overall calories from intermittent fasting will result in some weight loss, there is also a substantial effect on fat loss. This is due to higher levels of human growth hormone but also the significant reduction in insulin (insulin regulates your blood sugars) and the corresponding increase in norepinephrine – the main neurotransmitter produced by the sympathetic nervous system. These hormones initiate the breakdown of stored body fat to use as an energy source. This increases your metabolism; studies show this varies from 3.6 per cent at the low end, to 14 per cent at the higher end.

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Intermittent fasting practitioners reported increased energy, better digestion and sleep, and improvements to mood and motivation.
If these arguments fail to tempt you into fasting, take a moment to weigh up the benefits of maintaining ideal body weight. The scales tip so heavily in favour of being on the lighter side; staying slimmer is one of the most important things you can do for your health.

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