The report functions as a road map of sorts for physicians to prescribe fasting as a method of prevention or treatment for obesity, cancer, diabetes and heart disease.
Study author Mark Mattson, a professor of neuroscience at Johns Hopkins University, hones in on two types: Daily time-restricted feeding (eating 6-8 hours a day and fasting for 16-18 hours) and 5:2 intermittent fasting (fasting two days a week, usually capping a fasting day at 500 calories).
The catch? Most Americans don’t intermittently fast (the norm is three meals a day plus snacks) and thus physicians are less inclined to consider fasting a solution to a broad range of health conditions, according to the review.
Because the research is relatively new, the report advises physicians to monitor their patients throughout intermittent fasting and gradually increase the duration and frequency of fasting to guide their transition.
How it works
Intermittent fasting has been studied in rodents and overweight adults to improve health across the spectrum, though it’s not clear if those benefits are the result of weight loss.
Alternating between fasting and eating can improve cellular health, Mattson said, most likely by triggering metabolic switching. In metabolic switching, cells use up their fuel stores and convert fat to energy — “flipping a switch” from fat-storing to fat-saving.
Findings on intermittent fasting range in the diet’s effectiveness, but some studies in animals and humans have linked the practice to longer lives, healthier hearts and improved cognition.
The long-term effects of intermittent fasting require more research that isn’t available yet, and the studies that do exist are narrow. The clinical trials focused on overweight young and middle-age adults, so the benefits and safety can’t be generalized to other groups, the authors said.
Another thing: It’s a difficult diet to stick to, particularly in the United States, where the concept of three meals a day is “so ingrained in our culture” that a change in eating pattern often doesn’t cross doctors’ or patients’ minds, Mattson wrote.
It’ll almost definitely leave participants hungry, irritable and less able to concentrate, the study said.
“It’s human nature for people to want to reward themselves after doing very hard work, such as exercise or fasting for a long period of time,” he said. “So there is a danger of indulging in unhealthy dietary habits on non-fasting days.”
When the brain is deprived of food, appetite hormones in the hypothalamus, the brain’s “hunger center,” are released in a flurry and can trigger overeating.
But Mattson said the pain is temporary.
“Patients should be advised that feeling hungry and irritable is common initially and usually passes after two weeks to a month as the body and brain become accustomed to the new habit,” he said.