Could exercise be thwarting your weight loss goals?

You finish an hour at the gym and start thinking about a takeaway meal before you even reach the change room. It can feel as though exercise has simply made you hungry enough to eat back every calorie you burned.

The science is less straightforward. A meta-analysis of 20 studies found that exercise temporarily reduced ghrelin, the hormone associated with hunger, while increasing hormones linked to fullness, including PYY, GLP-1 and pancreatic polypeptide. A later systematic review found that this appetite-suppressing effect usually fades after 30 to 90 minutes.

That means exercise is not a reliable appetite-control strategy. It may create a short period when hunger is dampened, followed by a return to normal appetite. Over longer periods, the body can respond to substantial energy expenditure by increasing hunger as it works to restore energy balance.

A review of exercise training in adults above a healthy weight or with obesity found a small increase in fasting hunger. It found no clear or consistent rise in hunger after meals or across the day, and exercise did not substantially increase average energy intake. Feeling hungrier after exercising can therefore be a normal physiological response, not evidence that the body is somehow fighting the workout.

Short bursts of high-intensity exercise and moderate continuous exercise both temporarily suppressed appetite in a review of 13 randomised controlled studies. High-intensity exercise appeared to have a slightly stronger effect, although the difference was not consistent. The practical lesson is not that everyone should begin high-intensity interval training. Physical activity that people enjoy and can keep doing is more valuable than choosing a workout for a short-lived hormonal effect.