You woke up late, missed breakfast and now it’s been hours since your last meal — but instead of feeling ravenous, why does hunger sometimes cause nausea instead? It’s a feeling a lot of people have experienced, but one that’s difficult to understand. Why would your body find food less appealing, at a time when it needs it most?
Christine Lee, a gastroenterologist at Cleveland Clinic, told Live Science that there is a pretty simple explanation behind this phenomenon.
Dr. Lee is a board certified Pediatric Gastroenterologist and Transplant Hepatologist. Receiving her medical degree from Brown University in Providence, RI, Dr. Lee then joined the Boston Combined Residency Program at Boston Children's Hospital and Boston Medical Center.
Your stomach produces hydrochloric acid as a part of the long process of breaking down food, using what it can for energy and materials, and disposing of the rest. If you don't eat for an extended period of time, the hydrochloric acid can build up in the stomach.
"When it sloshes up into the esophagus, it can cause acid reflux, heartburn and nausea," Lee said.
Another set of possible reasons for feeling nauseous when hungry has to do with your body's network of signals for knowing when to eat. These signals are regulated by the endocrine system, a system of glands (including the pituitary gland, the thyroid gland and the pancreas) that uses the bloodstream for chemical communication.
Hormones generated by the endocrine system give your body the information it needs to keep its chemical levels balanced. For example, to maintain healthy blood sugar levels and support a wide range of bodily activities, you need calories. Your stomach sends signals to the endocrine system that trigger the release of hormones; these hormones tell the brain, "Give us more calories " or "That's enough." A lot of hormones are involved, but two important players are ghrelin and leptin.
"Ghrelin is supposed to cause hunger," Lee said. The hormone was discovered in 1999, but since then, researchers have identified ghrelin as a key player in a number of important processes in the body, including gut motility, gastric acid secretion, taste sensation and glucose metabolism.
Leptin has the opposite effect: It counters ghrelin by decreasing appetite. There are many other hormones involved in feelings of hunger, but the interplay between ghrelin and leptin is key in the healthy ebb and flow of appetite.
"When your body is in a normal state, these hormones auto-regulate," Lee said. "You should only have a few signals throughout the day gently reminding you to eat.”
As you eat, your body releases leptin, which signals that you're satisfied and don't need to be hungry for a while. In other words, your body needs food, so it produces ghrelin. This makes you hungry, so you eat. Then, your body doesn't need more food, so it produces leptin. This makes you feel full, so you stop eating.
But this chemical balancing act can be thrown out of whack if you ignore your hunger signals and don't eat regularly. Go long enough without eating, and your body will try to coax you into eating by producing more ghrelin.
"When the hormones go up, they're supposed to increase your appetite," Lee said. In most people, this is exactly what they do. But not always.
"Some people have higher sensitivities to hormonal levels," Lee said. Variation in sensitivity and other factors lead some people to experience light nausea when they're extremely hungry. Cases of more severe nausea symptoms, however, could hint at a disorder.
"If your signals are intense enough that you get nausea or pain, that could be your body telling you that you need to be screened for metabolic syndrome" — conditions such as high blood sugar, abnormal cholesterol, increased blood pressure and high blood sugar — which can lead to heart disease, Lee said.
Originally published on Live Science on Oct. 27, 2019 and updated on Aug. 25, 2022.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.
Grant Currin is a freelance science journalist based in Brooklyn, New York, who writes about Life's Little Mysteries and other topics for Live Science. Grant also writes about science and media for a number of publications, including Wired, Scientific American, National Geographic, the HuffPost and Hakai Magazine, and he is also a contributor to the Discovery podcast Curiosity Daily. Grant received a bachelor's degree in Political Economy from the University of Tennessee.
- Alice BallEditor