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. R
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 approach, which requires fasting for 16 hours a day; you’d eat between,
say, 11:30 a.m. and 7:30 p.m. 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 11 a.m. and
6 p.m.” (Here’s everything you need to know about the Warrior Diet.)
Intermittent fasting may be easier than traditional diets
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!” (Just make sure you’re aware of the possible differences in
intermittent fasting benefits for women.)
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.”
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. (This is what
you can drink while intermittent fasting.)
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.