After a day of fasting, people only eat about 10% more than they normally would, explains Krista Varady, PhD, a nutritional scientist who led the University of Illinois research. That 10% doesn't even come close to making up for the missing calories, she says, which is why people lose weight.
Fasting also alters body mechanisms for the better, says Courtney Peterson, PhD, assistant professor at Pennington Biomedical Research Center. "Fasting lowers levels of inflammation and puts the body into repair mode," she says. "Production of antioxidant enzymes increases, and that helps repair and recycle cells."
Want to give fasting a shot? These guidelines will help keep you safe.
Check with your doctor first.
You need to make sure it's safe for you to go without food for more than half a day at a time—for example, fasting is not for pregnant women or people with diabetes. "You can quickly deplete your body of electrolytes, including sodium, so fasting needs to be approached carefully," says Peterson.
Try the every-other-day approach.
Once you have the green light from your doctor, give Varady's plan a shot: Eat as much as you want on feast days, and then limit yourself to 500 calories on fast days—and be sure to choose high-quality, nutrient-packed foods such as lean meat and fresh produce. While this well-studied approach is safe, says Varady, people who eat frequent small meals or snack often may find the fast days intolerable. (Learn how to lose twice as much weight with The 2-Day Diet.)
Experiment with time-restricted eating.
This approach to fasting sounds more palatable to most people: To start, try limiting yourself to 12 hours of eating and 12 hours of fasting. Once you adjust, see if you can increase the number of hours you fast: In animal studies, weight loss and health benefits were higher when the feeding window was limited to 8 to 10 hours.
Always eat smart.
Although some plans don't dictate what you you can have when you're not fasting, don't use that as an excuse to subsist on ice cream and Oreos. "No matter what diet you're on, you should get the bulk of your calories from healthy foods, like veggies, lean protein and whole grains," says Peterson. "Your body needs nutritious food to function most effectively."
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Make sure you drink plenty of fluids.
You may not realize it, but food supplies at least 20% of your water intake. "If you're fasting, or even doing a modified, 500-calorie fast, you should drink 8 to 12 glasses of water every day," says Varady.
