Image copyright PA Image caption Researchers found eating a meal and exercising at the same time increases the feeling of hunger by a lot
Eating a meal and exercising at the same time increases the feeling of hunger in surprising ways, US researchers have found.
The study, led by Wake Forest Baptist Medical Center, found that exercise increases the brain’s use of a hormone called ghrelin – associated with appetite.
Ghrelin results in a rise in a certain signal in the brain called leptin, which induces hunger or satiety.
The new research could lead to better treatment for obese people, the study authors say.
Researchers say they also want to know if short- and long-term diets like these can compensate for the release of ghrelin.
What is ghrelin?
Research suggesting that ghrelin may act on different parts of the brain or body has been underway for decades, but its mechanisms are uncertain.
Ghrelin levels typically fall naturally when you stop eating, but in people with obesity this drop is not so large. It is now used by researchers to understand what gives rise to hunger and why it is strongly linked to obesity.
Image copyright PA Image caption Ghrelin results in a rise in a certain signal in the brain called leptin, which induces hunger or satiety
Dr Shlomi Levitsky said: “It has long been thought that obesity is related to declining appetite and abstinence from eating, but what we found is that when individuals exercise, the same leptin signal normally induces appetite.”
He added: “We want to make sure that short-term dieting can help overcome ghrelin-mediated appetite suppressions.”
Short term diets are limited
They are also looking into the role of exercise in the brain – though this is not as much of a focus as figuring out why exercise induces hunger and satiety.
Researchers looked at 39 overweight, obese and normal weight men in their 30s, 30s and 40s from a family health history cohort.
They have been allocated to take either a normal, balanced diet or a low-calorie, high-fat diet. The exercise was either daily 30-minute sessions at the gym or did not happen at all.
Researchers found that the amount of ghrelin increased between exercising and not exercising.
In this case, it was higher than for eating more but was not necessarily harmful. This indicated that the increase in ghrelin was particularly connected to eating rather than satiety.
The new study involved regular exercise, which kept blood levels of ghrelin similar to eating.
During the fasting phase of the study before the exercise began, ghrelin fell to about the same as when sitting and eating.
Further research is needed to establish whether changes in the amount of ghrelin associated with exercise are long-term or temporary.
How does the finding compare with previous research?
The study found that it is linked to eating, rather than an increased desire to eat.
Previously published research found a large change in ghrelin spikes and weight gain, and some research suggested that the increase was more short-term.
However, most studies have been done in animals, and it is unclear whether this could be a problem with humans.