You’re three-quarters of the way through a long run, during which you’ve had a couple of gels and a bar, but now your stomach is starting to feel empty, you want food and your mind begins to wander.
Maybe you think about something salty – or are you fantasising about succulent slices of watermelon and juicy orange wedges? Perhaps you are one of those people who can’t even think about taking on food while you’re actually running, but feel ravenous a short time after crossing the finish line?
Our bodies all react differently when put under stress by high intensity exercise and we all need to that post-run nutrition right – the interesting thing is how our stomachs and brains chat to one another to come up with the best plan without us even being consciously aware of it.
Research originally published in the American Journal of Clinical Nutrition provides some interesting insight into what shapes your mental menu choice while you’re engaged in exercise.
A team from the University of Birmingham asked 15 subjects to run on a laboratory treadmill at a modest-but-steady pace for 1 hour, and then put them in an MRI machine (fMRI), which measured their brain activity while they were being shown images of low-calorie and high-calorie foods.
The intrepid researchers 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 centres’ in the brain.
The impact of running on appetite and thirst
Even though they were given unlimited access to water, the subjects still reported feeling thirsty after finishing the 60-minute run, and this seemed to influence their subsequent reactions to the photos of food. As a result, their brain reward centres reacted more strongly to low-calorie foods (such as fruits and vegetables, which contain more water), than to the drier, denser high-calorie foods.
These results were backed up by a more recent review published by Science Direct and supported by the National Institute for Health and Care Research (NIHR), which collated the results of studies undertaken in previous years where an fMRI scan had been used to examine individuals’ neural responses to visual food cues in conjunction with an assessment of physical activity or a structured exercise exposure.
Authors of the 2023 review reported that it: ‘Provides evidence that habitual physical activity and structured exercise may influence brain food cue reactivity in regions linked to pleasure, motivation to eat, episodic memory and attention.’
The conclusion of this recent review stated that: ‘Structured acute and chronic exercise exposures appear to reduce brain food-cue reactivity in motivation- and reward-related regions particularly when viewing high-energy density food cues and may enhance the appeal of low-energy density food cues.’
The role of the stomach in appetite
The team from University of Birmingham who conducted the original research also found the ghrelin and peptide YY associations they had expected in the subjects’ stomach and intestines. Running basically 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, which is why so many runners struggle to even think about food during exercise.
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, yes your brain and stomach are talking to each other, and that has to be a good thing. And even though much has been written about your need for modest protein consumption after a hard workout, there’s a lot to be said for feasting on a fabulous fruit salad as well.