Physical activity is promoted for its benefit on fitness and helping burn up excess kilojoules. Now scientists are beginning to unravel secondary benefits it could have by dampening activation of brain regions that drive our desire for less-healthy high-kilojoule foods.

Physical activity has many health benefits and is a cornerstone of lifestyle advice to help with weight control. Being more active can cause a short-term increases in hunger soon after exercising, but longer-term it results in less hunger and of course more kilojoules burned.

Scientist have been probing into the brain to examine just how exercise could have direct effects on appetite and feelings of hunger. One interesting theory is that regular exercise may curb the activity of brain reward regions that light up and drive desire when we see food – especially the high kilojoule sweet and fatty variety.

Published in the journal NeuroReport, 37 healthy adults of varying exercise participation levels viewed pictures of different types of high- and low-kilojoule food while undergoing brain scans. Twenty five of the participants were regular exercisers, with the total range of weekly activity going from zero to 9 hours.

People with the highest levels of exercise showed brain scans with significantly lower responsiveness to high-kilojoule foods such as hamburgers, cake and ice-cream. The high-kilojoule foods just weren’t pushing their desire buttons.

This same group of higher-exercising people also reported that their normal day-to-day desire for high-kilojoule foods was lower than that of the less active people. In people where brain reward regions did light up when looking at pictures of food, there was a clear link to their self-reported initial desire for high-kilojoule foods, particularly those with a savoury flavour.

The results from this study are certainly interesting, but need the disclaimer that the research was only a cross-sectional snapshot of the lifestyle habits of a small group of people. A future study looking at how brain reward regions change over several months once someone embarks on a fitness plan would clearly be the next step.

What it all means

The role that exercise plays on weight loss may not just be through simple energy expenditure. Exercise is already known to have direct effects on brain structure and function including increased blood flow, new blood vessel growth and neurogenesis. Scientists are now beginning to discover that exercise may also be important in changing our desire and reward mechanisms for how we see food.