Intermittent fasting does not require a change in food choice or diet composition, instead it relies on time-restricted eating. Some people fast for 12 to 18 hours a day, while some may restrict their food intake a full day or more.
While an increasing number of people are trying to squeeze their meals into shorter time blocks in order to lose weight, there may be additional benefits aside from weight loss. Growing evidence suggests that intermittent fasting (IF) supports a healthy metabolism, heart health and brain health, as well as healthy blood sugar levels, which could reduce the risk of type 2 diabetes.
In 2018, researchers from the University of Alabama conducted a study with a small group of obese men with pre-diabetes. They compared a form of intermittent fasting called “early time-restricted feeding,” where all meals were fit into an early eight-hour period of the day (7 am to 3 pm), or spread out over 12 hours (between 7 am and 7 pm). Both groups managed to maintain their weight. However, after five weeks, the eight-hour group had much lower insulin levels and improved insulin sensitivity, as well as significantly lower blood pressure. The eight-hour group also reported a decrease in appetite.
A more recent review article published in The New England Journal of Medicine examined a compilation of past animal and human studies. The report serves as a guide for doctors who may be looking to prescribe IF to patients. It aims to clarify the science and clinical applications of IF in ways that may help physicians guide patients who want to try it.
One of the review’s authors, Mark Mattson, a professor of neuroscience at Johns Hopkins University, has studied intermittent fasting for 25 years and adopted the practice himself 20 years ago. Mattson hopes the article will offer insight into intermittent fasting and perhaps propel it into mainstream diet discourse.
“We are at 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,” he said.
Mattson points out that pre-clinical studies and clinical trials have shown that intermittent fasting has widespread benefits for many health conditions, such as obesity, diabetes mellitus, cardiovascular disease, cancers, and neurologic disorders. Animal models show that intermittent fasting improves health throughout the lifespan, whereas clinical studies have mostly involved short-term interventions that lasted a few months.
The review points to an array of research, including two recent pilot studies that found patients with multiple sclerosis who incorporated intermittent-fasting regimens reduced symptoms in two months. The article said that the anti-inflammation properties from intermittent fasting would also be expected to benefit rheumatoid arthritis sufferers.
Another study involving rats saw their average life span increase by 80% when they were fed alternate days from young adulthood. And a review of data from 1934 to 2012 showed restricted calories increased the longevity of rats by 14% to 45%, and 4% to 27% in mice.
Physical function may also be improved with intermittent fasting. Mattson said that despite having similar body weight, a study on mice on alternate-day fasting was found to have better running endurance than mice that had unlimited access to food. Balance and coordination also improved in animals on daily time-restricted feeding or alternate-day fasting regimens. In humans, young men who fasted daily for 16 hours lost fat while maintaining muscle mass while resistance training for two months.
The benefits aren’t just physical. The review also highlighted studies in animals that found intermittent fasting enhanced cognition in spatial memory, associative memory, and working memory. The review mentioned research that suggests alternate-day fasting and daily caloric restriction may reverse the adverse effects of neuroinflammation on spatial learning and memory.
Other evidence mentioned is a clinical trial where older adults on a short-term regimen of caloric restriction had improved verbal memory. In a separate study involving overweight adults with mild cognitive impairment, one year of caloric restriction led to improvements in verbal memory, executive function, and global cognition. A larger, more recent randomized clinical trial found that two years of daily caloric restriction led to a significant improvement in working memory.
Mattson said alternating between fasting and eating can improve cellular health, likely by triggering a metabolic switch, where cells use up their fuel storage and convert fat to energy, thus "flipping a switch" from fat-storing to fat-saving.
“Although we do not fully understand the specific mechanisms, the beneficial effects of intermittent fasting involve metabolic switching and cellular stress resistance. However, some people are unable or unwilling to adhere to an intermittent-fasting regimen. By further understanding the processes that link intermittent fasting with broad health benefits, we may be able to develop targeted pharmacologic therapies that mimic the effects of intermittent fasting without the need to substantially alter feeding habits.”
Maintaining an intermittent fasting regimen isn’t for everyone
The authors admit that incorporating the diet is a challenge, given the culture we live in. “Despite the evidence for the health benefits of intermittent fasting and its applicability to many diseases, there are impediments to the widespread adoption of these eating patterns in the community and by patients.” The review added that three meals with snacks every day is so ingrained in our culture that the thought of changing this eating pattern will rarely be contemplated by patients or doctors.
Because most physicians are not trained to prescribe specific intermittent-fasting interventions, the article notes that a good starting point for doctors is to suggest that patients gradually increase the duration and frequency of the fasting periods over the course of several months.
Source: The New England Journal of Medicine
December 26, 2019; 381:2541-2551 DOI: 10.1056/NEJMra1905136
"Effects of Intermittent Fasting on Health, Aging, and Disease"
Authors: R. de Cabo, et al.