How can intermittent fasting affect health?

Intermittent fasting may support gut, liver, metabolic, and weight health, but fasting that is too restrictive can disrupt hormones and fertility.

1. Gut microbes and clock genes: Time-restricted eating can help entrain circadian clock genes and may shift gut microbes in ways that support the gut lining and intestinal function; it may benefit people with IBS or colitis. 1 2

2. Fat loss, muscle, and weight management: An eight-hour eating window has been associated with mild calorie restriction and weight loss without calorie counting. Time-restricted feeding can also support weight maintenance or loss, though the cited discussion does not establish a specific muscle-maintenance effect. 3 4

3. Hormones and fertility: In men, time-restricted feeding lowered free testosterone in one study of highly active cyclists, and fasting combined with excessive exercise or insufficient calorie intake may harm testosterone and fertility. In women, inadequate body fat and low leptin signaling can interfere with ovulation; an overly short eating window may be a concern, so individual responses matter. 5 6

4. Liver and insulin health: Time-restricted feeding is linked with better liver health and may help reduce or potentially reverse non-alcoholic fatty liver disease; the discussion also describes positive effects on insulin profiles and blood-glucose regulation. 7 8

5. Suggested timing: Consider waiting at least 60 minutes after waking before eating, stopping food and liquid calories two to three hours before bed, and placing an approximately eight-hour eating window during the daytime. 9 10