A hormone that has been linked to overeating makes food appear more tasty, new research has found.
When volunteers were given a shot of the ghrelin hormone, pictures of food they were shown had a bigger effect on their brains.
Scans found that the hormone boosts the activity of "reward centres" in the brain which fuel desire.
The findings, published in the journal Cell Metabolism, suggest that these pleasure signals are an important drive toward eating.
Ghrelin levels in the gut rise before a meal and drop after eating, suggesting the hormone causes hunger and encourages people to eat.
Study leader Dr Alain Dagher, from McGill University in Montreal, said: "When you go to the supermarket hungry, every food looks better. Your brain assigns a cost versus benefit to every food item. Now, we've found that it is ghrelin that acts on the brain to make food more appealing."
"It's not one or two brain regions, but the whole network. Food pictures become even more salient - people actually see them better. People also remembered the food pictures better when ghrelin was high."
Treatments that disrupt ghrelin might hold promise for fighting obesity but because they would influence the brain's pleasure centres there is a risk they would impact on mood.