The concept of intermittent fasting may seem scary at first. Going many hours without food? Not even a snack to tide you over? Whether you refer to it as time-restricted eating or IF, the practice of going for a block of time without sustenance — and doing that on a consistent basis for at least a few weeks — has inspired numerous researchers to investigate one big question: Does it really improve your health? To find out, we explored the science behind intermittent fasting.
According to a number of studies, the answer seems to be yes. Although more research is needed to pin down all the physiological mechanisms that make this strategy beneficial, we’ve got a sampling of what researchers have discovered so far. Keep reading to discover the five potential benefits of intermittent fasting.
1. It May Help You Live Longer
Restrict your eating, lengthen your life? The evidence for the fountain-of-youth effect is promising. Researcher Mark Mattson, PhD, an adjunct professor of neuroscience at Johns Hopkins University School of Medicine in Baltimore, looked at numerous intermittent fasting plans and concluded that two in particular are especially effective: restricting your eating time to a six- to eight-hour window every day (so, only eating between 11 a.m. and 7 p.m., for example), or a technique called 5:2 fasting, that involves eating normally five days a week and then eating only one moderate-size meal two days a week.
Publishing the results in The New England Journal of Medicine in 2019, Mattson noted that people who followed these plans showed improvement in blood pressure regulation, resting heart rate, blood sugar regulation, inflammation, and overall resistance to stress. “Taken together, it’s not hard to see why results like that might lead to a longer lifespan,” he says. “The more that evidence like this builds up, the more it feels like a transition point for intermittent fasting from an interesting personal health strategy to one that may be added to medical school curricula alongside standard advice about healthy diets and exercise.”
Other mechanisms at play when fasting may positively impact longevity as well, including something called autophagy. Like taking out the trash, autophagy happens throughout the body: It’s the process of cleaning out damaged cells so that newer, healthier cells can take their place. The more optimized this mechanism becomes, the more benefits you tend to see, says Roberta Gottlieb, MD, director of molecular cardiobiology at the Cedars-Sinai Smidt Heart Institute and leader of the Gottlieb Research Lab. A 2017 study in the journal Cell Metabolism compared mice who ate whatever they wanted throughout the day with a group that ate the same amount of calories but only at two distinct intervals (they fasted the rest of the time). The researchers discovered that the fasting approach turned on autophagy.
“Parts of our cells become damaged, and some of our habits can prevent the body from being able to remove these, which means that cells begin to accumulate more and more debris,” Gottlieb says. (Imagine your cells starting to look like the inside of a hoarder house.) Those habits include eating junk food and skimping on sleep, she notes. In her research, fasting and calorie restriction as a combination can be effective for turning on the autophagy process.
2. It Helps Maintain Muscle Mass
For people who are carrying a significant amount of excess weight, simply losing pounds often results in health benefits. But a better weight loss strategy tends to be maintaining or increasing muscle mass and lowering body fat. Research shows this combination brings many advantages, including a lower risk of chronic diseases and better mobility as you age. Maintaining muscle as you age also helps ward off sarcopenia, which puts you at risk for various potentially fatal conditions, including falls.
Mattson says intermittent fasting can help because at a certain point, usually after several hours without food, the body stops relying on calories taken in through food and starts burning fat instead. Metabolic switching is the name of this process, and it can be a boon for reducing body fat overall. Studies have shown that intermittent fasting, especially time-restricted eating, spares muscle while burning fat.
“In the normal eating pattern for most Americans, we eat throughout our waking hours, including snacks, and that means the body is running on those calories, and then storing the rest in the form of glycogen [the stored form of glucose],” Mattson says. When there’s an abundance of glucose stashed in the body for later use, it turns to fat. That fat often doesn’t get utilized as an energy source without that metabolic switch. Mattson notes that can be even more problematic when you don’t exercise enough, since the fat will continue to get banked instead of burned.
Keep in mind, this balance relies on restricting the time frame that you eat, not on eating fewer calories. Being sure to consume adequate protein is also important. Failing to do so can have a negative effect on muscle mass.
3. It Boosts Heart Health in Many Ways
Thanks to improvements in blood pressure and blood sugar management (also known as insulin sensitivity), intermittent fasting can be beneficial for heart function, says Luiza Petre, MD, a cardiologist and assistant clinical professor of cardiology at Mount Sinai School of Medicine in New York, who practices intermittent fasting herself.
Research published in The American Journal of Medicine in 2021 found that time-restricted eating benefits heart health through multiple surprising mechanisms. For one, it tends to improve the body’s circadian rhythm, which in turn improves sleep. Considering that insomnia is strongly linked with higher blood pressure and heart disease risk, this is a major benefit for your ticker.
The Antioxidant Effect
Another mechanism for improved heart health, according to the researchers, is better maintenance of antioxidant levels in the body. Antioxidants are compounds in the body that scavenge free radicals. (Think of free radicals as a bunch of marauders, running around causing all sorts of cellular damage that contributes to disease.) When there’s an imbalance in antioxidants or your levels are low, that can lead to a condition called oxidative stress — those free radicals get out of control. Oxidative stress has been linked to a higher incidence of cardiovascular disease, so reducing its impact through strategies like eating healthy and exercising is important. Intermittent fasting is one more way of lowering oxidative stress; and this not only helps your heart, but also has an impact in lowering risks for diseases such as cancer.
Although researchers are still trying to figure out how IF affects specific antioxidants, a study in The FASEB Journal in 2019 found that, in general, intermittent fasting increases the antioxidant capacity of plasma and decreases enzymes related to oxidation. “Obviously, intermittent fasting doesn’t replace managing your heart health with your healthcare team, but it may optimize heart function in a way that both prevents problems and improves any existing issues,” says Petre. “Plus, what’s good for your heart is good for the rest of your body, so this may be one strategy that has profound ripple effects across every system.”
4. It Reduces Diabetes Risk and Fine-Tunes Hunger Signals
If you already have diabetes, it’s crucial to check with your doctor first before making a major change to your diet, including trying intermittent fasting. However, it may be worth having that conversation: Research published in the journal Clinical Diabetes and Endocrinology in 2021 found ample evidence that intermittent fasting can not only reduce body weight in people with type 2 diabetes, it also decreases fasting glucose, insulin resistance (where your body becomes numb to the effects of insulin), and levels of a hormone called leptin. It’s responsible for adjusting hunger based on how much energy you have stored.
When leptin production is working correctly, it tends to reduce hunger signals so you don’t overeat. That optimization can help regulate blood sugar, which leads to a range of effects like more energy and lower weight. For people with type 2 diabetes, it could also lead to less reliance on medications like insulin.
All of these advantages mean time-restricted eating may be helpful for reducing diabetes risk as well, especially if you’re in the prediabetes category, says Jason Fung, MD, author of The Complete Guide to Fasting. Of course, that also depends on what you’re eating during your feeding window, he says. “Intermittent fasting on its own can improve factors like insulin regulation, but if you’re eating highly processed, very high-calorie foods with little nutritional benefit, you’re not going to see many improvements from simply changing your eating window,” he adds.
5. It Bolsters the Immune System
An interesting study published in Metabolism Open early in 2022 looked at intermittent fasters during the holy month of Ramadan — when practicing Muslims go without food from dawn to dusk — with an eye toward how it might affect the immune system and protect against COVID-19 infection. The researchers found that there were multiple mechanisms by which “fasting has the potential to optimize the immune system function…as it suppresses chronic inflammation and oxidative stress, improves metabolic profile and remodels the microbiome.” While these changes may make it easier for the body to ward off COVID infection, more targeted research is needed (in the meantime, all other necessary precautions should be taken). In addition, several studies have shown intermittent fasting can reduce levels of pro-inflammatory cytokines and the risk of inflammatory diseases, including heart disease, cancer and fatty liver disease, which is on the rise.
A version of this article appeared in our partner magazine, The Complete Guide to Intermittent Fasting For Beginners.