Previous research has suggested that oxytocin is involved in appetite-reducing pathways in the brain.
The findings were presented at the 97th annual meeting of the Endocrine Society and confirmed the findings of previous animal studies demonstrating that oxytocin reduces food intake.
"Our results are really exciting," says lead investigator Dr. Elizabeth Lawson of Harvard Medical School in Boston, MA. "Further study is needed, but I think oxytocin is a promising treatment for obesity and its metabolic complications."
As well as reducing the number of calories that men consumed at a subsequent breakfast, the oxytocin nasal spray also improved certain metabolic characteristics such as insulin sensitivity - the body's ability to clear glucose from the bloodstream.
Oxytocin is widely referred to as "the love hormone" due to its association with parts of the brain involved in emotional, cognitive and social behaviors. Acts of intimacy, such as sexual intercourse and holding hands, stimulate the release of oxytocin in both men and women.
Experts have also demonstrated that oxytocin interacts with the same reward system that many drugs taken to produce euphoria act upon. This system is driven by the neurotransmitter dopamine.
While the oxytocin nasal spray used in the study has been approved for use in Europe, in the US, it can only be used in clinical trials. Oxytocin is, however, available for use in the US as a drug to induce labor.
Fewer calories consumed on average after using nasal spray compared with placebo
For the study, the researchers randomly assigned 25 healthy men with an average age of 27 to take a dose of either oxytocin nasal spray or a placebo after fasting. While otherwise healthy, 12 of the participants were overweight or obese and 13 had a healthy weight.
One hour after self-administering their treatment, the participants were served a breakfast of their choice, selected from a menu. Each meal option contained double portions, and after the meal was finished, the researchers measured how many calories each participant had consumed.
The participants then returned at a later date, and the experiment was repeated, with each participant receiving the opposite treatment to that they had previously received. In the 3 days preceding each experiment, the participants reported eating the same amount of food.
On average, the researchers found that the men ate 122 fewer calories and 9 g less fat at the meal after administering a dose of the oxytocin nasal spray in comparison with the placebo. The oxytocin nasal spray also appeared to increase the use of body fat as a fuel for energy.
The spray did not affect the participants' self-reported appetites or the levels of appetite-regulating hormones found in their bloodstreams. The researchers are, therefore, unsure precisely how the oxytocin affected the men's caloric intake.
Although the treatment that the participants received was randomized, the study is limited by its relatively small number of participants, its short testing duration and its observational nature, meaning that the researchers cannot determine the causes of their findings.
Dr. Lawson states future research will need to examine the effects of the nasal spray among women, as oxytocin has been demonstrated to have sex-specific effects. The effects of the nasal spray should also be tested for an extended treatment duration.
The study was funded by the National Institutes of Health (NIH), and Dr. Lawson received additional funding from a Massachusetts General Hospital Claflin Distinguished Scholar Award.
Recently, Medical News Today reported on a study suggesting that oxytocin may have a sobering effect against alcohol.