We’ve heard a lot of noise lately about intermittent fasting, with folks who believe eating and fasting in search of weight loss, longevity, better gut health and other health benefits could be key.
But does it really work? And is it good for you?
At its core, intermittent fasting is a pattern that features periods of fasting and eating. The premise is this: When our insulin levels drop far enough and for long enough, as they do when we fast, we’re able burn off fat.
There are a number of different intermittent fasting diets:
- liquid fasting, a 24-hour period where you ingest only liquids
- dramatic caloric reduction is dropping from 2,000 calories to 500 calories
- time-restricted eating, where you eat every day but during only a limited number of hours—maybe a six- to eight-hour window
- alternate-day fasting, where you fast for a day and then eat normally the next day
- weekend restriction limits calories during the week, but not on weekends
In addition to lower insulin levels—which over time leads to weight loss—there’s literature that suggests intermittent fasting may slow the aging process through weight loss, lower blood pressure and reduced cholesterol. Other research shows increased lifespan as well as protection against diabetes, cognitive decline, heart disease and some cancers.
But the bulk of this promising research has been performed only in cells and animals in the lab. Human studies that will show what happens to our bodies when we fast is still underway.
Early results show some types of fasting may have positive effects on blood sugar control, blood pressure, and inflammation. And fasting can lead to weight loss. Researchers are studying whether these beneficial changes are side effects of the weight loss or the fasting process.
For most of us, the main reason to try intermittent fasting is to lose weight. Remember Beyoncé’s body after her cayenne pepper, honey and lemon water diet a few years ago?
But “that doesn’t work for everyone,” said Vicki Catenacci, a nutrition researcher at the University of Colorado. “It takes a lot of focus. It takes a lot of math, and a lot of willpower. For some people, restricting calories every day may be the best approach. For others, it might be easier to not have to count calories every day and use an intermittent fasting strategy for weight loss.”
So how do you know if intermittent fasting will work for you?
For some, restricting food may cause problems. For example, studies have found people who regularly fast more than 16 or 18 hours a day have a higher risk of gallstones. They’re also more likely to need surgery to remove the gallbladder.
But eating for 12 hours and then fasting for 12 hours is likely safe for most people, experts say, though they caution against people trying fasting diets not based on research.
If you’re considering fasting, start with a chat with your health care provider. Some people, including those younger than 25, who are pregnant or breastfeeding, who take insulin or other medications to control diabetes, who have been prescribed medication that must be taken with food, who have a seizure disorder, who have eating disorders or who operate heavy machinery at work, shouldn’t fast at all.
Even if you give intermittent fasting a try, you still need to make healthy food choices. That means choose fruits, vegetables, beans, lentils, whole grains, lean proteins and healthy fats; drink lots of water; and avoid sugars and processed foods. Because when you eat matters, the experts say, but what you eat probably still matters more.