Published in the Journal of Neuroscience, the study is the first to demonstrate that this pain alleviating effect occurs while animals are ingesting food or liquid, even in the absence of appetite. Lead author, Peggy Mason, claims, “It’s a strong, strong effect, but it’s not about hunger or appetite. 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 any reason.”
In the conducted experiments, researchers gave rats 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 would trigger the animal to remove its paw from the floor. The researchers observed that the rats were much slower to raise their paw while eating or drinking, compared to tests when they were awake, but not ingesting anything.
The most surprising finding was that there was no difference in the delayed paw-lift response between when the rat was ingesting chocolate and when it was drinking water, despite the indications of previous research that sugary substances were protective against pain. By selectively inactivating a region of the brainstem called the raphe mangus, the researchesr were able to remove the effect of drinking on rat’s pain response. The brainstem controls subconscious actions such as breathing and perspiration.
Researchers believe this effect is also present in humans, but it has become detrimental in modern society given our easy access to pleasure foods. Opening up a bag of chips could activate the brainstem – subconsciously pushing you to continue eating until the bag is empty, even while realizing that such behavior is costly to you.
Mason adds, “We’ve gotten a lot more overweight in the last 100 to 150 years. We’re not more hungry; the fact of the matter is that we eat more because food is readily available and we are biologically destined to eat what’s readily available. Ingestion is a painkiller but we don’t need the sugar, so replace the doctor’s lollipop with a drink of water.