They found that when rats are stressed, deprived of food and then exposed to chocolate - they overeat.
"Our findings contribute to the understanding of how feeding behaviour is regulated," Dr M Flavia Barbano from the Universite Victor Segalen, Bordeaux 2 in France told Reuters
"Research in this field could help us to better establish the origins of the obesity epidemic that Western countries are facing today."
Working with laboratory rats, Barbano along with her colleague, Dr Martine Cador tested three aspects of eating behaviour: motivation (how badly did the animals want the food); anticipation (how excited were they to get it); and intake (how much did they eat), in relation to how hungry or satisfied the animals were and how palatable the food was. The researchers describe their studies in the journal Behavioral Neuroscience.
A "key observation" in this research, Barbano said, is that foods with a higher hedonic value (more palatable) induce food intake independently of whether the animal is in a food-satisfied or food-deprived state (a.k.a, homeostatic state).
For example, when presented with a chocolate breakfast cereal, food-sated animals ate almost as much as food-deprived animals. But when presented with bland lab chow, sated animals ate very little.
This shows that highly palatable food "is a strong motivator for both sated and restricted animals," Barbano said.
When palatable food and satiety overlap, "attractiveness overrides satiety - a phenomenon known to anyone who has ever stood in a buffet line."
The researchers also assessed the motivational behaviour in relation to tempting and not-so-tempting food and found that the animals ran faster to the food when they were either food-deprived or were running toward a bowl of chocolate cereal rather than a bowl of bland chow.
"...attractiveness overrides satiety - a phenomenon known to anyone who has ever stood in a buffet line"
Dr M Flavia Barbano,
Universite Victor Segalen, France
However, when the well-fed animals were presented with the chocolate cereal, they ran just as fast as the hungrier rats.
Anticipatory activity - how excited the animals become in advance of eating - "seems to be more related to the homeostatic state of the animals than to the hedonic properties of the food," the investigators say.
Even if the genesis of obesity is multifactorial - involving both genes and environment - "the increasing size in meal portions and the increased palatability of the food are variables to take into account when focusing in the actual epidemic," Barbano said.
"Also, palatable food is preferentially chosen in binge-eating episodes, in pathologies such as bulimia nervosa and binge eating disorder. We believe that understanding which variables might modulate feeding behavior will help us to understand how it can become deregulated and lead to a pathological behaviour."