In a recent study it was found that exercise increases people's desire to consume sugary foods such as doughnuts, cream cakes and chocolates. This craving would make it difficult to lose weight.
The finding suggests that nearly half of us could be 'predisposed' to crave high-fat, sugary foods after working out.
In tests, 34 men and women followed the same three-month weight loss programme involving supervised, calorie-burning exercises five days a week.
After each 50-minute session in the gym, they were shown photographs of different snacks and asked to choose their preference.
Researchers identified two different types of exerciser. One group tended towards healthier, low-fat foods such as rice, pasta and boiled potatoes.
The other showed 'increased cravings' for all kinds of food, but particularly sweet options such as cream cakes, doughnuts and chocolates.
The 14 volunteers who failed to achieve their weight loss target fell into the second category, called 'non-responders'.
Experts believe that these non-responders may have a built-in preference for eating high-calorie 'reward foods' after intense exercise.
This could be because exercise causes hormonal changes which increase their urge to consume excess sugar and fat.
"Further research may identify responders and non-responders with blood tests," the Daily Express quoted Professor Neil King, of the Queensland University of Technology, Australia, as saying.
The findings are published in the Journal of Obesity.