New study reveals a stomach-brain-appetite link.
What foods do you usually think about at the end of a workout? Oranges and watermelon, or a big piece of cake? Recently published research in the American Journal of Clinical Nutrition gives some insight into your likely choice.
The research group had 15 subjects run on a laboratory treadmill at a modest-but-steady pace for 60 minutes. Afterwards, the runners were placed in a functional MRI machine (fMRI) that measured their brain activity while they were being shown images of low-calorie and high-calorie foods. (If you’ve ever had a brain MRI, you’ll appreciate that this took some fancy work with mirrors to show subjects the food images.)
The team from Great Britain’s University of Birmingham hoped to detect differences they could relate to changes in stomach hormones and amino acids, specifically ghrelin and peptide YY. Previous studies had associated ghrelin and peptide YY with changes in appetite. But no prior exercise studies had mapped them to “reward centers” in the brain.
No one was surprised that the runners got hot and thirsty during their workout even though they were given as much water as they wanted. Nonetheless, they still felt thirsty after they finished the 60-minute run, and this probably influenced their reactions to the food photos: Their brain reward centers reacted more strongly to the low-calorie foods than to the high-calorie foods. This may have been because the low-calorie foods included more water-containing fruits and vegetables than the drier, denser high-calorie foods.
But the researchers also found the ghrelin and peptide YY associations they had expected in the subjects’ stomach and intestines. Running caused a decrease in ghrelin and an increase in peptide YY. High ghrelin concentrations are believed to increase appetite, while higher levels of peptide YY decrease appetite.
According to the authors, their study offers “the first direct evidence that exercise-induced changes in peripheral signals [i.e., from the stomach] related to appetite regulation and hydration status are associated with altered neural responses within brain reward regions.”
In other words, your brain and stomach are talking to each other. That has to be a good thing. And even though much has been written about your need for modest protein after a hard workout, there’s a lot to be said for fruit salad as well.