7 Proven Intermittent Fasting Benefits
Intermittent fasting is more than just a way to lose weight—narrowing the window in which you eat may help slow aging, lower cardiovascular risk, and improve sleep quality. Read on to learn more.
What is intermittent fasting?
Intermittent fasting—periods of voluntary abstinence from food and drink—is a broad term that can be applied to many different practices. This type of dieting has spurred many books and received a lot of attention in the last few years, since studies (mostly in animals) have shown that it may reduce the risk for several diseases as well as promote weight loss. Additional research, including a small study of four fasting people published in Scientific Reports in 2019, suggests that intermittent fasting may also help boost metabolism.
The most popular approach to intermittent fasting is the 16/8, which requires fasting for 16 hours a day. Another version, alternate day fasting (ADF), alternates 24-hour periods of fasting (which are actually very restricted 500-calorie diets) with days of eating freely. The 5:2 approach limits fasting to just two days a week, while the Warrior Diet follows a 20-hour fast with one large meal consumed at night. "Part of the confusion with intermittent fasting lies in the lack of a definition," says Robin Foroutan, RDN, a New York City–based registered dietitian nutritionist and spokesperson for the Academy of Nutrition and Dietetics. "To some people, intermittent fasting means that they fast every day, while to others it means they only eat between 11am and 6pm." Here's everything you need to know about the Warrior Diet, another type of intermittent fasting.
Intermittent fasting helps you lose weight without following a traditional, calorie-restricted diet
Research suggests that counting calories and limiting your food options can cause stress and increase cortisol production, which can subsequently lead to abandonment of the diet, feelings of deprivation, uncontrolled cravings, and weight regain. Adapting to intermittent fasting, a method of scheduled eating and fasting, relies strictly on time. Some people want more flexibility when it comes to losing weight, says William Yancy Jr., MD, program director for the Duke Diet and Fitness Center in Durham, North Carolina. "They don't want to think about dieting every day of the week, [and] they lose motivation after a certain period of time of restricting calories." Intermittent fasting works for people who like to follow rules, explains Elisabetta Politi, RD, nutrition director for the Duke Diet and Fitness Center. "Rather than saying, 'Just eat less,' we tell them not to eat after 6 p.m.," she says, "and for those who have the discipline, it works."
Intermittent fasting helps you keep the weight off over the long term
Following an intermittent-fasting diet may make it easier to maintain the weight you lost over the long term. A two-part study of 40 obese adults, published in Frontiers in Physiology in 2016, compared the combined effects of a high-protein, low-calorie, intermittent-fasting diet plan with a traditional heart-healthy diet plan. The results showed that while both diets proved to be equally successful in reductions in body mass index (BMI) and blood lipids (fatty acids and cholesterol), those on the intermittent-fasting diet showed an advantage in minimizing weight regain after one year. Check out these nutritionist-approved strategies for fitting more protein into your diet.
Intermittent fasting may help those at risk for developing diabetes
According to the U.S. Centers for Disease Control and Prevention (CDC), 84.1 million people in the United States have pre-diabetes, a condition that if not treated often leads to type 2 diabetes within five years. Losing weight, moving more, and eating a healthy diet can help fight off developing type 2 diabetes. "When you lose weight, you become more insulin-sensitive," says Politi. "It drives the blood sugar down."
When we eat, our body releases insulin into the bloodstream to supply the cells with energy, but those who are pre-diabetic are insulin-resistant, which means their blood-sugar levels remain elevated. Intermittent fasting may help those who are pre-diabetic because it requires the body to produce insulin less often, explains Foroutan. "If you are pre-diabetic or have a history of diabetes in the family, this type of diet can be helpful." Research has shown promise in backing up these claims: A study published in the journal Cell in 2017 found that a diet mimicking fasting cycles could restore insulin secretion and promote the generation of new insulin-producing pancreatic beta cells in mice with type 1 and 2 diabetes. While further research still needs to be done, early studies on human cell samples suggest similar potential. Here's how to understand the difference between type 1 and 2 diabetes.
Intermittent fasting helps sync circadian rhythms and fight off metabolic diseases
Your circadian rhythm, or your internal body clock, is a natural system that regulates feelings of sleepiness and wakefulness over a 24-hour period. Research published in the Annual Review of Nutrition in 2017 suggests that intermittent fasting may help us to stick with our body's circadian rhythm, and that can help with our metabolism. Eating certain foods before bed has also been linked to weight gain and sleep disturbances, especially when they cause acid reflux. "We know that insulin sensitivity is increased during the day, and we are less sensitive to insulin at night—the same goes for digestion," Foroutan says. "It makes you wonder if eating at night is working against our body clock." If you want to honor your circadian rhythm, she adds, you need to go to bed earlier and sleep so the body can repair itself.
Intermittent fasting may lower your risk for cardiovascular disease
According to the CDC, about 610,000 people die of heart disease in the United States every year—that's one in every four deaths. You can reduce your risk for heart disease by following a healthy lifestyle: eating right, exercising, not smoking, and limiting alcohol intake. Research also shows that intermittent fasting may help. "If you restrict calories every day, it improves cardiovascular risk, glycemic control, and insulin resistance," explains Dr. Yancy. In one small study of 32 adults, published in the Nutrition Journal in 2013, an alternate-day fasting regimen resulted in weight loss as well as cardiovascular benefits, including improved LDL cholesterol and triacylglycerol concentration. "The studies use alternate-day fasting, but keep in mind that fasting does not mean not eating—it means eating less," adds Dr. Yancy. This type of diet represents a different way of doing things, and it might appeal to some because they can restrict a couple of days of the week rather than every day. "As an obesity physician, I like to have options for people, because people are different," Dr. Yancy says. "If it appeals to you, let's try it!" Here are more ways to reduce your risk of heart disease.
Intermittent fasting may slow down the aging process
Research shows that intermittent fasting benefits can mimic the effects of very low-calorie diets, which are good for anti-aging, says Foroutan. One study published in the journal Cell Metabolism in 2014 found that fasting can delay aging and help prevent and treat diseases. It revealed that fasting triggers adaptive cellular stress responses, which result in a better ability to cope with more stress and counteract disease. "Low-calorie diets increase mitochondrial stress, and the benefit is anti-aging," explains Foroutan. "The better your mitochondria (the powerhouse of our cells) works, the better your body works." Find out more weight-loss tricks worth borrowing from fad diets.
Intermittent fasting works best for certain people
Intermittent fasting can produce the greatest benefits on those who are overweight, but people who have plateaued with their weight-loss efforts might find that intermittent fasting can help jump-start their metabolism and help with their progress, says Foroutan. It can also benefit those who have digestive problems. "If you notice that your digestion is sluggish in the evening or if you have digestive problems at night, eating earlier and fasting overnight can help," she says.
Sometimes trying something different like intermittent fasting is enough for some people to get back on track with their weight-loss goals, says Politi. "One of my patients lost 30 pounds because she stopped eating late at night," she says. "She discovered the source of her weight gain was that she was eating junk food at the end of the day." For successful long-term weight loss, you have to have that "aha!" moment, adds Politi: "When you recognize what has been the cause of weight gain, it is empowering." Don't miss these other proven strategies for breaking a weight-loss plateau.
Intermittent fasting isn't for everybody
If you're an all-around healthy person, there is no risk in trying intermittent fasting. "But anyone with an eating disorder, a history of eating disorders, or body dysmorphia should not try intermittent fasting," says Foroutan. People with type 1 diabetes, women who are pregnant or breastfeeding, and those taking prescription medication that has to be taken at a specific time with food are also not candidates for intermittent fasting. One of the biggest downfalls of intermittent fasting, says Foroutan, is that it can be tough on your social life, especially if you like to dine out.
Intermittent fasting may affect your exercise regimen
It is not safe to exercise strenuously on days when you are fasting, says Dr. Yancy. "If you are eating only 25 percent of your daily calories and still exercising, you will suffer on those days," he says. Your body needs energy from glycogen stores to exercise, and if these levels are low, you will feel weak. Also, when you have low levels of glycogen, your body will break down protein (the building blocks of muscle) for fuel, resulting in muscle loss. "While it is not as difficult to exercise the day of your fast, it is difficult the day after you fast because your energy stores are depleted from fasting," he adds. Another problem with intermittent fasting is that many people get hungry after exercising, and that can lead to breaking the fast. "Timing your meals can help you achieve weight loss and weight control, but it is important to fuel your body when you are more physically active," says Dr. Yancy. If intermittent fasting seems too ambitious, learn the tiny diet changes that can help you lose weight.
- Cell Metabolism: "Fasting: Molecular Mechanisms and Clinical Applications"
- Scientific Reports: "Diverse metabolic reactions activated during 58-hr fasting are revealed by non-targeted metabolomic analysis of human blood"
- Robin Foroutan, RDN, a New York City–based registered dietitian nutritionist and spokesperson for the Academy of Nutrition and Dietetics
- Psychosomatic Medicine: "Low Calorie Dieting Increases Cortisol"
- William Yancy Jr., MD, program director for the Duke Diet and Fitness Center in Durham, North Carolina
- Elisabetta Politi, RD, nutrition director for the Duke Diet and Fitness Center
- Frontiers in Physiology: "Comparison of High-Protein, Intermittent Fasting Low-Calorie Diet and Heart Healthy Diet for Vascular Health of the Obese"
- CDC: "New CDC report: More than 100 million Americans have diabetes or prediabetes"
- Cell: "Fasting-Mimicking Diet Promotes Ngn3-Driven β-Cell Regeneration to Reverse Diabetes"
- Annual Review of Nutrition: "Metabolic Effects of Intermittent Fasting"
- CDC: "Heart Disease Facts"
- Nutrition Journal: "Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial"
- Cell Metabolism: "Fasting: Molecular Mechanisms and Clinical Applications"