Ask the Doctors: Junk food cravings are tied to hormones, circadian cycle

Research has linked sleep and our endocrine system, and the connection plays out with two hunger hormones in particular: ghrelin and leptin.

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Craving junk food is not uncommon when you’re sleep-deprived.

Craving junk food is not uncommon when you’re sleep-deprived.

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Dear Doctors: Is there some reason I crave junk food when I’m really tired? I’m working double shifts. If I don’t sleep enough, all I want is donuts and pizza. My husband says it’s because they’re my favorite foods, and they’re easy.

Dear Reader: Research has found a link between sleep and the endocrine system, and the connection plays out with two hormones in particular: ghrelin and leptin. Each has an important role in regulating hunger.

Ghrelin, which stimulates appetite, is produced and released mainly from the tissues of an empty stomach. Its roles include facilitating fat storage, regulating blood sugar and helping with memory retention.

It also makes you feel hungry and has come to be known as the hunger hormone.

Leptin suppresses appetite. It’s stored in adipose tissue — 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.

The ebb and flow of these hunger hormones is tied to the cycle of daylight and darkness — the circadian cycle that 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 and can make sweet and fatty foods so tempting.

Research has linked sleep deprivation and an increase in the production of neurotransmitters known as endocannabinoids, which can lead to an increased feeling of hunger.

Another answer arises from an intriguing study by Northwestern University researchers that found 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.

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, you’ll feel 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 and Dr. Elizabeth Ko are internists at UCLA Health.

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