Regular exercise reduces the appetite for fatty foods, new research suggests.
The British trial found that high levels of activity acted as a "buffer" - fending off cravings for unhealthy fare.
Scientists said the findings suggest that those who got a "high" from exercise were less likely to feel tempted by junk food.
The study, led by the University of Leeds, tracked 180 individuals in the lab.
First their cardio respiratory fitness levels, body composition and metabolic rates were measured, with participants classed as having high, moderate or low activity levels.
This was followed by two intensive days in the lab, where their appetite, tastes and and fullness levels were tracked throughout a day's eating.
Overall, the fittest group found fatty foods between 10 to 15 per cent less desirable than the couch potatoes, the study found.
Researcher Dr Graham Finlayson said: "It is the first study looking at people's food cravings and the reward value of food.
"What we found is that there is a clear relationship between the amount of moderate to vigorous physical activity - raising your heart rate and building up a sweat - and the desire to eat high fat food."
"People that did the least exercise found high fat food the most rewarding while those that did the most found it less appealing," he said.
"I don't think that's been known before."
The findings were presented at the European Congress on Obesity in Porto.
Researchers said the trial could not prove that activity levels had a direct impact on appetite, as the findings were observational.
"We can speculate that people who already get their daily reward and enjoyment from exercise, are less likely to succumb to the temptation of fatty food," said Dr Finlayson.
"People are looking to get a certain amount of reward in their lives and you can get it from different sources.
"Getting a high from exercise means people aren't looking to get a reward elsewhere.”
Steven Ward, chief executive of ukactive, said: “We know physical activity is key to weight management by burning calories, but it’s a win-win that reaching for your gym shoes means you’re less likely to reach for the snack cupboard.
“With obesity and physical inactivity placing unprecedented strain on the NHS, it’s essential our next government tackles the root of the problem by getting more people, more active, more often.”