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The ten-hour window
Time-restricted eating leaves what you eat alone and changes only when. The 10-hour window is the sweet spot most people can manage, for example from 11 in the morning to 9 at night or from 8 to 6. Black coffee and black tea are allowed because they don't cause a sugar spike.
What studies show
Studies in mice and rats show help with metabolism and energy management. In people, there is some evidence of a small effect on weight, lower inflammation, and reported improvements in energy and mood. A study of 130,000 people doing it for two weeks found that most managed it, with better mood and energy and less hunger, largely because people snacked less, especially just before bed.
Why it might work
The idea behind it is that the body repairs itself at night as stress hormones fall, and the gut does the same. If the gut rests for 14 hours, other microbes come out like a repair team, clean up the gut wall so it isn't leaky, and reduce inflammation.
It isn't right for everybody. Snackers can find it very hard, and some people prefer an early finish while others want the social life of an evening meal.
Why does the gut need an overnight rest?
Between meals, the small intestine runs a cleaning cycle called the migrating motor complex, in which waves of muscle contraction sweep leftover food and bacteria toward the colon. The cycle repeats roughly every 90 minutes during fasting and stops when a person eats. Joseph Szurszewski at the Mayo Clinic first described the pattern in dogs in 1969. Reduced activity of this cycle is associated with bacterial overgrowth in the small intestine.
Why does the same meal hit harder at night?
Insulin sensitivity and glucose tolerance follow the body's circadian rhythm and fall in the evening. In a 2015 study in PNAS, Christopher Morris and colleagues at Brigham and Women's Hospital found that identical meals eaten at 8 PM produced higher blood sugar and less fat burning than the same meals at 8 AM. The rise of melatonin at night also dampens insulin release.
Where did time-restricted eating come from?
In a 2012 paper in Cell Metabolism, Satchidananda Panda's group at the Salk Institute fed mice a high-fat diet, either whenever they liked or within an eight-hour window. The mice limited to eight hours were protected from obesity, high insulin, and fatty liver, despite eating the same calories. That result launched the human trials that followed.
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