How Brain and Gut Chemicals Affect Fullness
Here’s how the chemicals in your gut and brain stoke your desires and sense of fullness:
The beta cells secrete the hormone amylin along with insulin in order to regulate blood glucose after meals. Amylin slows the liver’s glucose production and the rate at which food empties from your stomach, which helps prevent post-meal blood glucose spikes. It also helps you to feel full after eating. But people with type 1 diabetes have no beta cell function, so they can’t produce amylin or insulin. Those with type 2 may have insufficient amylin because the beta cells don’t work as well. The lack of amylin may interfere with feeling satisfied after a meal, and the body’s available insulin may not be enough to deal with all the glucose from the meal.
If you’re feeling anxious, the stress hormone cortisol will prime the dopamine system to want high-calorie foods, says Ashley Gearhardt, PhD, assistant professor of clinical psychology at the University of Michigan. When you try to cut calories too abruptly, you’re likely going to be hungry and stressed, she says, and that combination can sabotage healthy eating.
This neurotransmitter (essentially a messenger that carries signals between nerve cells) is associated with addictive and reward-based behaviors, says Gearhardt. “That’s part of the reason why when you walk past your favorite bakery, you suddenly experience a big, intense craving for that food, even if you’re full,” she says. “We get this burst of dopamine that can engage us.”
The peptides (a group of hormones) in your digestive system play a role in hunger. If you’re low on calories, your gut peptides will prime the dopamine system in your brain to be on the lookout for food. According to Susan Roberts, PhD, a professor of nutrition at Tufts University, the sight and smell of food releases the hunger-producing hormone ghrelin, increasing the addictive chemicals in the brain so you feel ready to eat—even if you don’t need to.
The appetite-suppressing hormone leptin tells you when you’re full. It blunts the dopamine system’s response, serving as the body’s stop signal. But in people with metabolic syndrome—a group of risk factors that increases the risk for type 2 diabetes, heart disease, and stroke—this signal doesn’t seem to work as well, says Gearhardt.
Opioids are responsible for the pleasure that comes from consuming food. Research has shown that repeated consumption of high-calorie treats can actually diminish the intense pleasure you feel. “It might be why you feel the desire to eat bigger and bigger portions,” says Gearhardt. “You’re not getting the same reward you once did.”