Intermittent fasting is simply cycling your eating patterns with periods of fasting. There are three types of intermittent fasting that have been studied considerably: alternate-day fasting, whole-day fasting, and time-restricted feedings.

Alternate-day fasting is when you fast for 24 hours and then feed for 24 hours. Whole-day fasting is when there are one to two days of complete fasting with zero calories. Time-restricted feedings require fasting for 16 to 20 hours and then feeding for four to eight hours. Alternate-day fasting is the most studied and promising for weight loss because you don’t increase your calorie intake on feeding days. Most successes revolve around an overall decrease in caloric intake, but research has mixed results when it comes with maintaining lean body mass during weight loss.

Studies have shown that whole-day fasting is the least reliable intermittent-fasting strategy. Research has shown that after six months of whole-day fasting, the results weren’t positive compared with a regular diet’s.

Time-restricted feedings, like those done during Ramadan (when Muslims fast completely from sunrise to sunset for one month), are the most studied type of intermittent fasting. Weight loss was certain but at the cost of lean body mass. More recent studies looked beyond the Ramadan fasting. One in particular that examined 16-hour and eight-hour fasting cycles for eight weeks showed significant fat mass loss while maintaining lean body mass.

Intermittent fasting may have a seat at the table with athletes, but it should be well-planned. It’s also highly recommended to be supervised by a registered dietitian nutritionist and possibly a team, which may include a psychologist, a primary care physician, and a personal trainer.

To maintain lean muscle mass during fat mass loss, it is recommended that you have adequate protein, engage in resistance training, and lose weight at an appropriate slow and steady rate.

Jonathan Valdez, R.D.N., A.C.E.-C.P.T., is the owner of Genki Nutrition, a nutrition wellness and counseling business in New York City.

Man intermittent fasting and timing his meals and feeding windows

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