Junk food cravings tied to hormones, circadian cycle
Q: Is there some reason I crave junk food when I'm really tired? I'm working double shifts, and if I don't sleep enough, all I want is doughnuts and pizza. My husband says it's because they're my favorite foods and they're easy, but it feels different than just that. What can I do?
A: You're not imagining things when it seems that the allure of sweet and fatty foods gets stronger when you're tired or run down. Research has found a link between sleep and our endocrine system, and the connection plays out with two hormones in particular: ghrelin and leptin. Each has an important role in the regulation of hunger.
Ghrelin, which stimulates appetite, is produced and released mainly from the tissues of an empty stomach. It has many roles, including facilitating fat storage, regulating blood sugar and helping with memory retention. Most important in this context, though, is that it makes you feel hungry. In fact, despite ghrelin's many other duties in the human body, it has come to be known as the “hunger hormone.”
Leptin, by contrast, suppresses appetite. It is stored in adipose tissue, which is commonly known as body fat. Once released, it circulates in the blood and reaches the brain. One of leptin's jobs is to signal the brain to create the feeling of being full after eating.
In addition to certain triggers that are associated with food intake, the daily ebb and flow of these two hunger hormones is tied to the daily cycle of daylight and darkness. That's the 24-hour period we know as the circadian cycle, which cues so many of the body's essential functions. When you're sleep-deprived, you've fallen out of sync with your circadian rhythms. This has the effect of suppressing the leptin levels that let you know you're full and increasing the secretion of ghrelin, which amps up appetite. The result can be the spike in hunger you're feeling that's making sweet and fatty foods so tempting.
Past research has found a link between sleep deprivation and an increase in the production of neurotransmitters known as endocannabinoids. These particular neurotransmitters also play a role in scent and feeding behavior, and can lead to an increased feeling of hunger.
Another answer arises from an intriguing study from Northwestern University. Researchers found that the olfactory system — the sense of smell — goes a bit haywire in people not getting adequate sleep. A sharp increase in sensitivity to scents was followed by muddled brain messaging related to energy needs. The researchers suspect this could lead to a craving for energy-dense foods. With that kind of internal signaling, doughnuts and pizza would easily win when competing with salads and fresh fruit. No wonder we reach for the takeout menu and the snack drawer when we've missed out on sleep!
While the occasional comfort food “cheat” is fine, we think you'll feel a lot better with healthier fare. Plan ahead with meals that include high-quality protein and complex carbs, which will help you feel full and satisfied.
• Dr. Eve Glazier is an internist and associate professor of medicine at UCLA Health. Dr. Elizabeth Ko is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoctors@mednet.ucla.edu.