Intermittent fasting, or IF, has become one of the fastest-growing nutrition trends of the year, topping lists ranging from of celebrity-endorsed eating plans to Google searches by curious dieters.
There's also an increasing number of studies that back up the hype with scientific evidence, suggesting IF can ward of disease, help control blood sugar, and lead to weight loss even without cutting calories, according to a review article published December 26 in the New England Journal of Medicine.
For the article, researchers reviewed more than 70 published studies about the most common types of IF — the 5:2 method (eating normally for five days a week and fasting the other two days), fasting every other day, or limiting meals each day to a smaller time period (often six to eight hours and fasting the other 16 to 18 hours of the day).
The authors found that IF of all types can help slow aging and age-related illnesses like cancer, heart disease, and diabetes. It can also help with weight and fat loss.
Even more promising, the benefits of IF aren't only seen in people who lose weight. The researchers think an additional process, called metabolic switching, is the cause of most, if not all, of IF's benefits, according to the study.
The findings mark "a transition point where we could soon consider adding information about intermittent fasting to medical school curricula alongside standard advice about healthy diets and exercise," lead author Mark Mattson, a neuroscientist at John Hopkins Medicine, said in a press release.
"Metabolic switching" could provide benefits even after you've eaten again
Typically, a type of simple sugar called glucose is human's main energy source. We get glucose from food, and especially carbohydrates, which our digestive systems convert into glucose, according to the Harvard T.H. Chan School of Public Health.
During fasting, though, the body has to resort to a different energy source so the liver breaks down fatty acids into ketones, which can be used for fuel instead.
Intermittent fasting, however, allows the body to switch between the two sources of energy, glucose and ketones, in a process called "metabolic switching," the new research found.
Alternating fuel sources is believed to be responsible for many of the benefits of intermittent fasting, according to the researchers, since it sparks a lasting cellular response to protect the body from harm. This includes reducing inflammation, boosting metabolism, and protecting against oxidative stress, which is linked to illness associated with aging, from cancer to Alzheimer's.
These and other benefits seem to persist even after you've begun eating normally again.
Experts are still figuring out how best to implement fasting to maximize its benefits
Earlier studies have found IF can help with athletic endeavors, including one of young men finding that those who fasted for 16 hours a day were able to reduce body fat while maintaining muscle mass during two months of resistance training. A separate study found that mice who fasted every other day had better running endurance than those who didn't.
The pattern may even help protect brain health and prevent cognitive decline in older people, according to several clinical trials that linked intermittent fasting to improvements in memory.
Despite the evidence of IF's benefits, though, there are a few obstacles in the way of making it a widespread health solution for the general public.
First, according to the researchers, it hasn't yet become widely accepted to eat fewer than three meals a day, although that may be changing. The availability of cheap, high-calorie snack and other food might make it difficult for people to adhere to a fasting lifestyle, too.
What's more, the medical community doesn't yet have an established protocol for "prescribing" fasting in the same way that it now encourages people to eat a balanced diet and exercise.
It's also important to note fasting may not be for everyone. The process can lead to irritability, grogginess, and stress, and can be risky for people vulnerable to eating disorders.
More research needs to be done on the long-term effects of intermittent fasting, but study author Mattson — who has studied the health impact of intermittent fasting for 25 years, and adopted it himself about 20 years ago — believes the robust evidence so far suggests the eating pattern could one day be a standard part of any healthy lifestyle.
Read more:
8 signs your intermittent fasting diet has become unsafe or unhealthy
There's more evidence that intermittent fasting could help you lose weight without eating any less
