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Limiting food intake and engaging in exercise are highly effective strategies for weight loss. People who are obese are often sedentary, however, due to physical limitations and a lack of motivation to exercise. Compelling findings from a new study in mice suggest that ghrelin, a hormone linked to appetite, may increase motivation to engage in exercise.
Ghrelin, which is produced primarily in the stomach, stimulates appetite, increases food intake, and promotes fat storage in mice and humans. It is often referred to as the “hunger hormone” and is linked to reward-driven behavior. Previous studies have shown that ghrelin administration increases activity in mice in anticipation of food.
The current study involved mice that were fed on a time-restricted eating schedule (twice daily) versus mice that were allowed to eat freely throughout the day. Both groups of mice ate roughly the same amount of food each day. The mice that were fed on the time-restricted schedule were more motivated to engage in voluntary exercise and ran on an exercise wheel for longer periods. The increase in the animals' activity corresponded to increases in ghrelin levels. Conversely, inhibiting ghrelin attenuated the animals' motivation to exercise.
Hunger-related behaviors such as increased activity are essential to animals in the wild or human hunter-gatherers because they must forage and seek out or hunt for food. Tapping into these ancient hormonally-driven behaviors may help resolve modern-day concerns of obesity and lack of exercise. However, a small study in humans demonstrated that time-restricted eating decreased morning levels of ghrelin (and subsequently appetite), so more studies on the effects of time-restricted eating and ghrelin in humans are needed.