Animals, including humans, evolved to coordinate bodily biochemistry and metabolism with the daily cycles of sleep and wake, light and dark. For humans, hunting and feeding were daylight activities followed by long periods of dark and sleep. Only in recent evolutionary history have we mastered our environment to allow prolonged waking periods with constant access to food. There is growing evidence (reviewed by Manoogian and Panda) confirming that our modern eating habits, with food consumption from breakfast until well into the night, are disrupting our metabolic regulation and are contributing to metabolic syndrome (obesity, high blood sugar, high blood pressure, and high cholesterol). Many people eat a large, late dinner and then continue to snack until bedtime. For these individuals, the daily feeding interval between the first food in the morning and the last food at night may be 15-16 hours, leaving only 8-9 hours of continuous fasting per day. Studies in both mice and insect models suggest that restricting the feeding interval to a period of less than 12 hours each day improved metabolic health. Surprisingly, the benefits accrue even without reducing total calories. Simply restricting the time period for food intake and allowing a longer fasting period each day appears to have significant beneficial health effects. Recent studies are now exploring the effects of time-restricted eating (TRE) on humans.
To get a baseline look at TRE effects on humans, Gabel et al. did a 12-week study on 23 obese adults. During the test period their food intake was confined to an 8-hour daily period with 16 fasting hours each day. After the test period the participants lost an average of 2.6% of body weight with no reported adverse effects. Other similar studies also saw weight loss and metabolic improvement, though some studies utilized TRE intervals as short as 6 hours daily, a period not likely to be practical for most people. More realistically, a 10-12 hour feeding interval could potentially be adopted without too much difficulty. A recent 10-hour feeding interval study of individuals already being treated for metabolic syndrome showed that even 12 weeks on this schedule promoted weight loss, lowered blood pressure, and reduced the atherogenic lipids that cause arterial plaque. Clearly longer term studies are needed to assess the extent of benefits and the persistence of the beneficial effects. While some individuals might chafe at a restricted eating period, many people could likely adjust to confining food intake to a 10-12 hour period without too much disruption of their daily routine. Interestingly, a mouse study found that the benefits of the weekday TRE were not lost by taking weekends off, a schedule that would surely be more palatable to most of us. If the human TRE trials continue to show positive results, TRE may someday be an important component of a healthy lifestyle, along with a balanced diet and sufficient exercise.