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 As a runner, I’ve long been intrigued by what gets me high during my runs. Endorphins, you say? Yes, I’m well aware of those and bless those endorphins. But, I have to say, there’s nothing quite as satiating as a good run and as a scientist by training, I was convinced that there was more to that feeling than endorphins. Turns out, there is. It wasn’t too long ago that I came across an article published by researchers in Montreal that studied the interplay between the brain and a hormone called leptin¹.

Levels of this fat hormone rise when you consume food and drop when you don’t. Rodents with low leptin levels ran faster and longer in the laboratory, suggesting that somehow the hormone controls your (and my) will to run¹. These findings demonstrate the relationship between the runners' high and leptin levels. Leptin teams up with another molecule in the brain called the signal transducer and activator of transcription 3 (STAT3) to flip that running switch in the brain^1,2. These buddies work in tandem to cut the brain’s access to a gratifying chemical called dopamine^1,2. This latter hormone promotes the sensation of elation and satisfaction after eating a big meal. When our leptin levels rise, so do levels of STAT3 and dopamine, and we feel great. When levels of dopamine drop, due to lower levels of leptin and STAT3, we are wired to seek food and maintain energy levels^1,2.

Basically, falling leptin and STAT3 levels in the brain trigger reward-seeking mechanisms. Great, so how does this have anything to do with runners? Well, runners, especially marathon runners, tend to eat less. This means they tend to have lower levels of leptin in their bodies². So now you can get the gist of how the runners' high and leptin work together: Low leptin > Low STAT3 > Low dopamine > High motivation to go look for food, or increase physical activity, and induce that euphoric feeling that makes me and all runners want to get back outside and run. Every. Single. Day. 

1. Fernandes et al. (2015). Leptin suppresses the rewarding effects of running via STAT3 signaling in dopamine neurons. Cell Metab, 22(4), 741-749. PMID: 26341832.
2. Akpan, N. (2015, September 1). Scientists find a fat hormone toggles a runner's high. PBS Newshour.