Adolescent weight gain on popular injectable contraceptive may depend on micronutrient intake

With no good explanation for what causes the pounds to pack on, or a way to predict who will gain weight, physicians counsel all their teen DMPA patients to eat less food. But in some adolescent patients, even low-calorie diets don't appear to stave off the increase in body mass index (BMI).

"Studies have looked at race, socioeconomic factors, calorie intake -- and not one of these has been conclusively linked to the kind of weight gain trajectory that we see in some girls who are on DMPA," said Andrea Bonny, MD, an adolescent medicine expert at Nationwide Children's Hospital.

However, a study conducted by Dr. Bonny shows that the answer may be found in the quality of a teen's diet versus the quantity. In her research, teens using DMPA were less likely to gain weight if their diets were rich in three nutrients: dietary fiber, magnesium and linoleic acid -- a type of omega 6 fatty acid. Girls whose diets were lower in those nutrients tended to gain weight rapidly and consistently over a period of one year.

Dr. Bonny's research team analyzed the girls' exercise habits and daily intake of calories, fat, protein, carbohydrates as well as different types of micronutrients. BMI was checked at the beginning, middle and end of the study. The researchers did not find a correlation between increased BMI and any of the other dietary or lifestyle factors, but observed a connection between less weight gain and intake of specific micronutrients.

"Fiber, magnesium and linoleic acid are typically found in a diet rich in legumes, leafy vegetables, nuts and fruits -- basically, healthy fresh food," said Dr. Bonny. "The message we need to be giving girls taking DMPA is to eat better, not less."

Clues from post-menopausal metabolism

Research indicates that one in four DMPA users will experience excessive weight gain (greater than 5% of their original BMI) within the six months of their first injection. For these girls, lean body mass is steadily replaced by fat tissue -- and effect that does not plateau over time.

Dr. Bonny, also an assistant professor of pediatrics at The Ohio State University College of Medicine, has been studying hormonal contraceptives for more than 15 years. She says she has always been curious about why DMPA caused such significant weight gain in some teens, but not others.

"I knew it couldn't be as simple as just telling these girls to eat less food. There are literally thousands of dietary factors that could be at play."

Because DMPA significantly lowers estrogen production, Dr. Bonny turned to nutritional research that had been done with post-menopausal women for clues. Many studies in this population indicated that food intake couldn't explain why some women tended to gain weight after menopause more than others. Further, there was research suggesting that micronutrient consumption could impact post- menopausal metabolism.

With support from Ohio State's Center for Clinical and Translational Science (CCTS), Dr. Bonny's research team was able to comb through past research to identify the top 30 nutrients that were most likely to influence the growth of fat tissue in a low-estrogen environment. Dr. Bonny's team then enrolled 45 adolescents from a local clinic, and analyzed their diets over a 12 month period while they were on DMPA.

While most girls in the study did gain body mass and lose lean mass, Dr. Bonny says her data strongly suggests that there is more at play than just the amount of food consumed -- which is the first step in predicting and possibly preventing weight gain among teen DMPA users.

A pretzel a day…

While DMPA remains a very popular choice among urban teens, a healthy diet can be hard to come by.

"Many girls who live in urban areas don't always have access to fresh produce," said Dr. Bonny. "The message of 'eat better' is a good start, but we need to keep looking for options and answers."

Dr. Bonny's hopes her next study will offer both. She is currently planning a clinical trial to see if a pretzel snack containing linoleic acid and fiber can help obese girls on DMPA maintain or lose weight versus overweight girls on DMPA who don't eat the snack. Experts at Ohio State's Food Innovation Center created the micronutrient-packed treat just for Dr. Bonny's study.

"I think as we explore this more, we may find that some people's fat tissue has a biological sensitivity to DMPA, and that the micronutrients may offer a sort of protective effect," said Dr. Bonny.

Results of the study were published in the Journal of Pediatric and Adolescent Gynecology. Dr. Bonny's research was supported by a mentored training grant from the National Institutes of Health as well as the CCTS. Collaborators include Martha Belury, PhD, of Ohio State's College of Education and Human Ecology and Hannah Lange, MPH, of Nationwide Children's Hospital, who was the clinical trial coordinator and study co-author.