Oxytocin Nasal Spray Encourages Men To Eat Fewer Calories

man eating
A nasal spray of oxytocin helped men consumed 122 fewer calories and cut their fat intake by 9 grams. Guian Bolisay, CC BY-SA 2.0

The so-called love hormone may help people tame their love affair with food. A new study conducted by Harvard University researchers has found oxytocin, the hormone that gets released when we hug another person and has new moms feeling warm and fuzzy about their babies, reduced caloric intake in a group of men.

Most of the research into oxytocin has looked at its potential for treating social disorders, such as autism. The hormone is also frequently used to induce labor. Less studied is its role in appetite suppression. Prior animal studies have shown an increase in metabolic function after scientists gave rats a dose of oxytocin; however, little evidence has so far shown that it can be a reliable weight loss tool for humans who overeat.

“Our results are really exciting,” said lead investigator Dr. Elizabeth Lawson, assistant professor of medicine at Harvard Medical School. “Further study is needed, but I think oxytocin is a promising treatment for obesity and its metabolic complications.”

Twenty-five men comprised the study, 12 of whom were overweight or obese while 13 were of a healthy weight. On two separate visits, the men were given a menu of breakfast options to select a meal. Before their first visit, a random half of the group received a nasal spray containing the drug, which is made by Novartis and currently approved in Europe but limited to clinical trials in the U.S. The other half received a placebo spray. Before their second visit, the sprays were switched. Then they ate.

Results showed that regardless of weight, men who took the nasal spray containing oxytocin ate 122 fewer calories on average and reduced their fat intake by nine grams. Their bodies also seemed to do a better job using body fat for fuel, the researchers found. No side effects were reported in either the placebo or the oxytocin group.

Based on self-reports, Lawson and her colleagues determined appetite suppression wasn’t a mediating factor in getting people to eat less. By all accounts, nothing seemed that different. This is a departure from other studies that have looked more closely at specific brain chemistry, and have found a similar effect from oxytocin that’s already been observed in the so-called hunger hormones, ghrelin and leptin.

The human stomach produces these hormones alongside the vagovagal reflex, a signal that gets sent to the brain once food enters the stomach. Oxytocin neurons, the brain cells responsible for handling food intake and energy, seem to work in a similar way. There may also be a component related to reward. In 2013, researchers showed in rat models that the brain instinctively relies on pleasure-producing foods in order to compel the animal to eat. Oxytocin seems to quiet that response. “It may be that oxytocin has a satiating effect related to certain components of diet rather than a general effect,” the researchers wrote in their report. “Thus, the balance of evidence suggests that oxytocin might have a role in limiting the intake of palatable food by suppressing the activation of the reward pathway.”

Yet to be discovered are the effects oxytocin has on women. Lawson and her team looked only at men, and the delicate mix of gender-specific hormones makes this a crucial variable for later study. Lawson and her team will present the findings at the upcoming Endocrine Society's 97th annual meeting in San Diego.

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