Leptin is a fat cell-derived hormone that signals the brain when the body has enough fuel and energy. Researchers have revealed that this satiety hormone is indeed a reality behind the euphoric feeling that gives runners a motivational boost in the middle of their workout. The study findings suggest that falling leptin levels send a hunger signal to the brain's pleasure center to generate the rewarding effects of running.
Senior study author Stephanie Fulton from University of Montreal said, "Based on these findings, we think that a fall in leptin levels increases motivation for physical activity as a means to enhance exploration and the pursuit of food."
The study findings also suggest that people with lower fat-adjusted leptin levels, such as high-performance marathon runners, could potentially be more susceptible to the rewarding effects of running and thus possibly more inclined to exercise. During lab experiments, mice with reduced leptin signalling in the brain logged nearly twice as many miles on a running wheel compared with normal mice.
Low leptin levels have been previously been associated with exercise addiction, fast marathon times and training status in humans and also correlate with greater running speed and duration in mice. These new findings could also have clinical implications for anorexia. Previous research has shown that leptin signalling in the brain's reward center inhibits wheel running in a rat model of anorexia-induced hyperactivity. Moreover, people with anorexia have low fat-adjusted leptin levels that are associated with increased restlessness and hyperactivity.
Fulton said, "We speculate that the mechanism described in this work could potentially underlie the hyperactivity associated with anorexia." In future studies, Fulton and her colleagues will test their hypothesis of running reward being associated with food seeking.
The study appeared in Cell Metabolism.