With everyone from tech C-suiters to celebrities swearing by it, intermittent fasting reigns as one of the trendiest dietary practices. But unlike a lot of fad diets, it seems to be backed by real science. A new review of past studies on intermittent fasting from New England Journal of Medicine suggests it has benefits for diabetes, heart disease, and other health conditions, and may boost cognitive and physical performance, Newsweek reports.
Before delving into the findings, a primer on the buzzy practice: Intermittent fasting is a broad umbrella term encompassing any regimen that involves switching between fasting and feeding periods. The most widely-researched are daily time-restricted feeding, when you feed only during a certain time window each day; alternate-day fasting, when you fast every other day; and 5:2 intermittent fasting, when you fast two days a week, according to Newsweek.
Rafael de Cabo, a scientist at the National Institutes of Health, and Mark Mattson, a neuroscientist at Johns Hopkins University, analyzed previously-published human and animal studies on intermittent fasting. The human studies correlated it with improvements in insulin resistance, obesity, high blood pressure, abnormal blood lipid levels, and inflammation. These benefits were so significant, they couldn’t be explained by caloric reduction alone.
Among many other studies, the review authors cited research on the residents of Okinawa, Japan, who have low rates of obesity and diabetes, and have long lifespans, possibly because they practice fasting. The researchers also described study that showed intermittent fasting to heighten resistance to stress by enhancing neuroplasticity, or the brain’s ability to adapt and change, CNN reports. In another study, young men lost fat, but not muscle, when they engaged in resistance training for two months while fasting for 16 hours a day.
De Cabo and Mattson saw benefits in animal studies, too. According to Newsweek, intermittent fasting enhanced various types of memory, while alternate-day fasting and daily caloric restriction reversed the negative effects of obesity and diabetes on certain aspects of cognition in such studies. Other studies have shown intermittent fasting to extend lifespan in rodents.
Although the mechanisms of how intermittent fasting benefits health aren’t entirely clear, the review authors think it may activate a metabolic switch that causes cells to begin using fat, rather than sugar, as energy, Newsweek explains.
The problem is that most people in the US eat three meals a day with snacks in between. In fact, this eating pattern is such a deeply instilled cultural norm that many patients and doctors don’t even consider intermittent fasting as an option, CNN reports. The practice can also cause irritability, hunger, and a diminished ability to concentrate, making it hard to follow, although the review's authors noted that these obstacles tend to subside within a month.
If you're interested in trying intermittent fasting, check in with your primary care physician before getting started. In a previous Mic story, Alex McDonald, a family physician specializing in sports medicine and internal medicine in San Bernardino, California, advised against the practice for people with diabetes, certain metabolic syndromes, or kidney problems. Same for those younger than 18, underweight, prone to developing an eating disorder, pregnant, or breastfeeding, per Men’s Health. Despite the promising findings on intermittent fasting, it’s still important to approach it safely and responsibly.
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