Research Shows Intermittent Fasting Has Some Health Benefits — But Experts Say The Risks Aren’t Worth It

by JR Thorpe
Ashley Batz/Bustle

While the internet is full of dubious wellness trends, one in particular is often cited as having science to back it up: Intermittent fasting, where participants restrict their eating to certain hours of the day, or certain days of the week. Some science does show that intermittent fasting has some benefits for heart health and neurogenesis. A recent study by the Mount Sinai School Of Medicine published in Cell found that practicing intermittent fasting may reduce acute inflammation and help inflammation-related chronic illnesses. But nutritionists and eating disorder specialists tell Bustle that aspects of intermittent fasting can be dangerous, because they can damage people's relationships with food.

One of the most concerning problems with intermittent fasting, according to experts, is that it can disconnect your body from its natural feelings of hunger and satiety. "Only eating during a specific time frame each day disconnects us from our bodies," Alissa Rumsey, an NYC-based dietitian and founder of Alissa Rumsey Nutrition and Wellness, tells Bustle. "It causes people to disregard hunger cues, which then means once they are allowed to eat, they are starving and it can be hard to stop eating." The body has its own internal clock moderated by many external factors, including sunlight and sleep, that dictates when we feel hunger.

Experts are concerned about the impact of restrictive eating schedules on our internal clocks — and, by extension, on other aspects of health. "Restricting your eating to only certain times during the day ignores your body's needs, leaves you undernourished, and could cause the pendulum to swing to the other extreme once you do have permission to eat," nutritional therapist Emily Fonnesbeck, RD, tells Bustle. "This type of dysregulated, haphazard and chaotic eating pattern negatively impacts hormone balance, immunity, digestion, and sleep patterns. While intermittent fasting may appear healthy, it has the very real potential to make you unwell."


Restricting eating patterns so closely can also lead to a cycle of bingeing and fasting, experts say. "Intermittent fasting can damage your relationship with food by putting you into a restrict-binge cycle," Christy Harrison, MPD, RD, a dietician and expert on disordered eating, tells Bustle. "Decades’ worth of research has shown that fasting and other forms of restrictive eating increase people’s likelihood of binge eating, because our bodies have powerful biological mechanisms that kick in when they sense that we’re in danger of starvation. When our energy intake is too low, those mechanisms are triggered." People who fast, Harrison says, may end up eat feeling unbalanced around food.

There are also biological consequences to skipping meals; Rumsey tells Bustle that radically reducing your food intake prompts an increase in your cortisol levels, which initiates fat storage and the breakdown of muscle. (Cortisol is the "stress hormone.") Further, Harrison also points out that "these behaviors can lead to full-blown anorexia, which affects people of any size." Physically or mentally, the body isn't built to withstand starvation patterns.

Intermittent fasting's supposed health benefits also don't measure up to what the science says. "Intermittent fasting is a sensationalized version of what we know to be true about overnight fasts," Fonnesbeck tells Bustle. "Having a break from eating for eight to 12 hours does improve metabolic profiles (blood sugar and blood lipid levels). However, you wouldn't need to skip any meals or snacks to get the benefits." (A break from eating for eight to 12 hours is more or less a break from eating during the time when you're sleeping, and that's it.) The problem, she says, is that without consistent or adequate nutrition, this metabolic process can "backfire." Not eating overnight makes sense; intermittent fasting, in general, may not be.

The major issue with intermittent fasting is that people often approach it not as a way to gain neurological benefits, boost heart health, or reduce inflammation, but as a quick way to lose weight. "The main reason why my clients have been interested in utilizing intermittent fasting has been as a means of losing weight," Tessa Nguyen RD LDN, a chef and registered dietician, tells Bustle. "In my experience, intermittent fasting has only been detrimental to my clients’s relationships with food."

And whether or not intermittent fasting induces weight loss, chances are that that is a temporary change. "We have more than 60 years’ worth of evidence showing that within five years, up to 98% of people who’ve lost weight end up gaining it all back, and likely gaining back more weight than they lost," Harrison says. "That makes dieting a recipe for weight cycling — the yo-yo cycles of loss and regain."

Weight cycling can raise the likelihood of heart disease, cancer and other conditions. "Some evidence suggests that all of the excess mortality risk we see for certain diseases in high-weight people can be explained by weight cycling alone," says Harrison — in other words, people might experience health problems not because of their weight, but because of crash dieting itself.

The overall picture on intermittent fasting shows that it might have some medical benefits, but that the risks may outweigh the benefits. "When losing weight is the sole goal, intermittent fasting becomes a way to start obsessing over the constriction of your food choices and intake," Nguyen says. "Instead of listening to your body cues and eating when you naturally feel hungry, your life begins to center around when and what you can and cannot eat." It's more helpful, experts say, to work towards intuitive eating, where you try to respond to your body's natural cues for nutrition, get enough sleep, reduce stress, and exercise as a way to feel good.

For experts on nutrition and health, intermittent fasting looks like an old story in new clothes: promoting a supposedly "healthy" ideal that fat-shames women. "Intermittent fasting is a socially acceptable way to engage in restrictive and disordered eating," Harrison says. "It’s disguised as health-promoting behavior, which can mean that people who are truly suffering from disordered eating fly get praised for behaviors that are hurting them." And

If you or someone you know has an eating disorder and needs help, call the National Eating Disorders Association helpline at 1-800-931-2237, text 741741, or chat online with a Helpline volunteer here.