Researchers get to grips with how oxytocin alters our brain's response to food.
As such, people sometimes refer to it as the "love hormone."
This hormone increases the contraction of the uterus during labor and stimulates milk production.
Most discussions about oxytocin focus on its role during childbirth, but it also affects other aspects of bodily functioning, including our relationship with food.
This hormone weakens the brain's reward signals for food, and it affects our eating behavior and metabolism.
According to recent research, which the team presented on Monday at ENDO 2019, the Endocrine Society's annual meeting in New Orleans, LA, oxytocin alters how people with obesity process images of high-calorie foods.
Obesity rates continue to rise
The worldwide prevalence of obesity has nearly tripled since 1975, according to the World Health Organization (WHO). In 2016, almost 2 billion adults were overweight, more than 650 million of whom had obesity.
The WHO use body mass index (BMI) to define being overweight and having obesity in adults. BMI is a calculation that involves dividing the body mass of an individual by the square of their body height.
- Overweight is a BMI higher than or equal to 25.
- Obesity is a BMI higher than or equal to 30.
The Centers for Disease Control and Prevention (CDC) reported that obesity affected about 93.3 million adults in the United States in 2015–2016. Obesity has an association with a range of health conditions, including heart disease, stroke, type 2 diabetes, and certain types of cancer.
Obesity also has a substantial economic impact. The CDC estimated that the annual medical cost of obesity in the U.S. was about $147 billion in 2008, and the average medical cost for people with obesity was $1,429 higher than it was for those of a healthy weight.
How oxytocin affects reward areas
Oxytocin may be a promising drug treatment for obesity. Past research showed that oxytocin nasal spray, which is not yet an approved treatment in the U.S., interacts with brain circuits that play a role in eating behavior.
"Knowing how the drug exerts its effects is a critical step toward establishing oxytocin as a drug treatment for overeating and obesity," says Dr. Liya Kerem, the study's lead investigator, who is a pediatric endocrinologist at MassGeneral Hospital for Children and a researcher at Massachusetts General Hospital, both in Boston.
To build on their prior findings, which indicated that oxytocin reduces the activation of part of the brain's reward system called the ventral tegmental area (VTA), the researchers analyzed how oxytocin affects the connectivity between the VTA and the rest of the brain.
The Nutrition Obesity Research Center at Harvard, the Boston Nutrition Obesity Research Center, and the National Institutes of Health funded the new study.
The researchers recruited 10 young men who were overweight or had obesity but were otherwise healthy. The participants made two visits to the research lab where they received a single dose of either oxytocin nasal spray or a placebo.
The participants were unaware of which treatment they received. After 1 hour, they looked at images of high-calorie foods, low-calorie foods, and nonfood objects while they underwent functional magnetic resonance imaging (fMRI). This neuroimaging technique measures changes in blood flow in the brain.
Compared with the placebo, oxytocin weakened the functional connectivity between the VTA and brain areas relating to food motivation when the participants saw pictures of high-calorie foods. There were no reported side effects of this treatment.
"This study is exciting because it shows that oxytocin modulates the pathways in the brain specifically during their responses to highly palatable, rewarding foods."
Lead investigator Dr. Liya Kerem
Dr. Kerem explained that individuals with obesity have "abnormally hyperactivated brain reward areas" when they look at images of high-calorie foods, even when they are full. This fact explains why we may be able to use medications such as oxytocin to treat obesity.