Many people say they experience an energy boost while doing intermittent fasting.Jacob Lund/Shutterstock
It’s odd to think that depriving yourself of a necessity for life might be one of the most powerful ways to transform your health. Yet there’s more and more evidence for the idea that fasting could have powerful health benefits for both the body and brain.
There are many different forms of fasting, ranging from going extended periods without food to consistently eating less (perhaps cutting caloric intake by 20%) to intermittent or periodic fasting.
But of all these different kinds of fasting, intermittent fasting is very likely the most popular and certainly the trendiest one. Celebrity adherents include Hugh Jackman, Tim Ferriss, and Beyonce. In Silicon Valley, whole groups of self-optimization-obsessed biohackers meet to collectively break their fast once a week, and executives at companies like Facebook say fasting has helped them lose weight and have more energy.
The hard part about classifying “intermittent fasting” is that there are a number of different forms of this kind of fast. Intermittent-fasting regimens range from allowing yourself to consume calories only within a certain span of the day, likely between six and 12 hours, to eating normally five days a week and dramatically cutting calories on two fasting days, to taking a 36-hour break from food every week.
The different forms that these fasts can take mean that much of the research showing benefits might be true for one of these fasts but not necessarily others. Yet there is good research on several of these fasts indicating that the benefits of intermittent fasting go beyond weight loss. There may be real long-term disease-fighting health improvements.
Here’s what we know so far.
Several studies suggest that intermittent fasting can do more than help people lose weight; it also may improve blood pressure and help the body process fat.
For one small study, researchers had overweight participants either cut calories every day or eat normally five days a week and consume only 600 calories on their two fasting days.
Both groups were able to lose weight successfully, but those on what’s known as the 5:2 diet did so slightly faster (though it’s unclear if the diet would always help people lose weight faster).
More significant, those from the intermittent-fasting group cleared fat from their system more quickly after a meal and experienced a 9% drop in systolic blood pressure (the “regular diet” group had a slight increase in blood pressure).
In another study, where researchers intentionally gave people enough food that they wouldn’t lose weight, doctors found that intermittent fasters who ate all their calories within one window improved their blood pressure and blood sugar levels.
There may be evolutionary reasons why depriving ourselves of food for some time makes us feel energetic and focused.
“Hungry,” from an evolutionary perspective, isn’t lifeless or drained. It’s when our bodies and brains need to function at maximum capacity.
“It makes sense that the brain needs to be functioning very well when an individual is in a fasted state because it’s in that state that they have to figure out how to find food,” Mattson told Business Insider. “They also have to be able to expend a lot of energy. Individuals whose brains were not functioning well while fasting would not be able to compete and thrive.”
Periodic fasting may make it easier for us to burn fat and enter ketosis.
Blood samples have shown that people who fast from 12 to 24 hours at a time enter a state called ketosis — when their bodies start to derive more energy from fat, Mattson told Business Insider in another interview.
The more you enter this state, the better your body gets at using fat as fuel. For that reason, some people try to trigger ketosis with “keto” diets that involve consuming a lot of fat. But, according to Mattson, fasting is a significantly more effective way of boosting ketone levels.
Intermittent fasting may strengthen neural connections and improve memory and mood.
human brain connectomeHuman Connectome Project, Science, March 2012.
Many people who fast intermittently say that at times they feel clearer and more focused while fasting.
There’s real science to back up the idea that being “hungry” gives you a sense of focus. Entering ketosis triggers the release of a molecule called BDNF, which strengthens neurons and brain connections linked to learning and memory.
That’s one of the reasons researchers have suggested that ketogenic diets (both the fasting kind and the fat-heavy kind) could be useful for people fighting degenerative brain diseases like Alzheimer’s. That also could explain the clarity or focus some people feel after fasting. It may provide a mood boost as well.
Some research indicates that intermittent fasting may help convert body fat to brown fat, which helps burn off excess weight.
According to one recent study, periods of intermittent fasting — taking breaks from food — sped up the metabolism of mice. In the process, fat in their bodies was converted to brown fat, a healthier type of fat that helps burn away white fat, which is what we think of as unhealthy body fat that builds up.
This is just a study in mice, meaning more research would be needed before we could say the same phenomenon is happening in people. But because brown fat is associated with burning off unhealthy fat — and also with other health benefits, including a faster metabolism, better blood sugar levels, and lower risk for certain chronic diseases — this may explain some of the health benefits associated with fasting.
