Scientists suspect that one element of the obesity epidemic is that the brains of obese people respond differently to images of delicious, calorically dense foods. Obese individuals’ brains seem to light up at the sight of donuts, pizza, and other calorie bombs, even when they’re no longer hungry.
Some studies have suggested that this heightened activity might predispose people to overeating. Today, nearly 40 percent of American adults are obese, and obesity is predicted to become the leading cause of cancer among Americans, replacing smoking, within five or 10 years. (It’s still not clear yet which comes first—the obesity or the overactive brain activity.) “Part of the reason for the obesity epidemic is that people eat when they’re not hungry,” says Elizabeth Lawson, an associate professor of medicine at Harvard Medical School and a neuroendocrinologist at Massachusetts General Hospital.
A remedy for this over-activation in the brain might come from an unexpected source: oxytocin, the brain chemical often associated with love and social relationships. Oxytocin is sometimes called the “cuddle hormone” because it’s released during sex, childbirth, and breastfeeding. People who are in the early stages of falling in love have higher levels of oxytocin than normal. The drug ecstasy also increases concentrations of the hormone in the blood.
Oxytocin has a variety of other surprising functions. A form of the chemical, Pitocin, induces labor, and another form might help treat stomach pain. Early studies have suggested that the hormone might boost social skills among kids with autism. Now Lawson and other researchers are investigating whether oxytocin might also prevent overeating.
Lawson and her colleagues recently showed images of high-calorie foods to 10 overweight and obese men. She found that the regions of the brain involved in eating for pleasure lit up when the men viewed the images. A dose of oxytocin, compared with a placebo, weakened the activity in those regions, and it also reduced the activity between them. Meanwhile, oxytocin didn’t have that effect when the men viewed images of low-calorie foods or household items. Lawson’s colleagues presented the research, which has not yet been published in a peer-reviewed journal, last month at Endo 2019, the Endocrine Society’s annual meeting.
“One of the key ways oxytocin works in limiting the amount of food that we eat is that it speeds up the satiety process, or reaching fullness,” says Pawel Olszewski, an associate professor of physiology at the University of Waikato, in New Zealand, who was not involved with Lawson’s study. “Then, oxytocin works through brain areas that are associated with the pleasure of eating, and it decreases our eating for pleasure.”
That’s just one of the ways oxytocin shows potential as an obesity treatment. Previously, Lawson and her colleagues found that the hormone improves insulin sensitivity and encourages the body to use fat as fuel. Lawson’s other studies have shown that oxytocin reduces activation in the hypothalamus, an area of the brain that controls hunger, and increases activation in areas of the brain associated with impulse control. To Lawson, the results together suggest that the hormone creates less of a need to eat, reduces the compulsion to eat for fun, and improves impulse control when it comes to actually reaching for that second slice of cake. Oxytocin, in other words, appears to make food seem less rewarding.
Other researchers have found that oxytocin might weaken alcoholics’ dependence on alcohol, drawing parallels to the hormone’s effects on how some obese people’s brains perceive food. A study published in the journal PLOS this month showed that oxytocin cut the desire to drink among alcohol-dependent rats. It’s not clear what this anti-drinking element of oxytocin has to do with its love-hormone properties, if anything.
So why can’t we just pick up bottles of oxytocin at CVS? For one thing, most of these studies have been very small; 10 is a minuscule sample size. They’ve been largely conducted on men, so future research would need to be expanded to women. The mechanism behind oxytocin’s effects on eating behavior and metabolism needs to be clarified, and the safety of using the hormone long term needs to be established.
The way that Lawson’s and many other studies have been conducted is by putting oxytocin in a nasal spray and attempting to shoot it directly toward the brain. But it’s not clear how much of the drug the person is actually getting through this kind of application, and researchers are still working on making it more precise. To answer some of these questions, Lawson is currently conducting an NIH-funded randomized controlled trial that will administer oxytocin to obese men and women for eight weeks.
Finally, even if all these studies are successful, it’s important to remember that there are myriad reasons—social, economic, biological, cultural—that people become obese, addicted to food, or addicted to other substances. An oxytocin treatment might only work for some of them, and even if it did, not all obese people desire to lose weight. “Its effectiveness may depend on the reason for why the obese individual is obese,” Olszewski says.
Still, a drug that helped even a fraction of America’s 93 million obese people would be a major breakthrough. If all this research bears results, many years from now, there may be another reason to love the love hormone.