People often eat food to feel better, but researchers have found that eating chocolate or drinking water can blunt pain, reducing a rat's response to a hot stimulus.

This natural form of pain relief may help animals in the wild avoid distraction while eating scarce food, but in modern humans with readily available food, the effect may contribute to overeating and obesity.

"It's a strong, strong effect, but it's not about hunger or appetite," Mason said. "If you have all this food in front of you that's easily available to reach out and get, you're not going to stop eating, for basically almost any reason."

In the experiments, rats were given either a chocolate chip to eat or had sugar water or regular water infused directly into their mouth. As the rat swallowed the chocolate or fluid, a light-bulb beneath the cage was switched on, providing a heat stimulus that normally caused the animal to lift its paw off the floor.

Mason and Foo found that rats were much slower to raise their paw while eating or drinking, compared to tests conducted while they were awake, but not eating.

Surprisingly, the researchers found no difference in the delayed paw-lift response between when the rat was eating chocolate and when it was drinking water, despite previous research indicating that only sugary substances were protective against pain.

"This really shows it has nothing to do with calories," Mason said. "Water has no calories, saccharine has no sugar, but both have the same effect as a chocolate chip. It's really shocking."

Source: University of Chicago Medical Center