14 DAY TRIAL // A new study carried out by researchers at the Oregon National Primate Research Center at Oregon Health & Science University, contradicts the common belief according to which oral contraceptives cause weight gain.
For their research, the scientists used the next best thing after the human body, a group of rhesus macaque monkeys from the OHSU Oregon National Primate Research Center.
Rhesus macaques actually have a reproductive system almost identical to humans, and unlike human studies, in this case more variables can be controlled and measured in advance, to obtain meaningful results.
At the beginning of the eight-month study period, half of the monkeys had a normal weight and the other half were obese.
During the study period, the animals were given oral contraceptives, in doses adjusted to their weight, in order to imitate the dosage in humans.
The researchers followed weight, food intake, body fat, lean muscle mass and activity levels.
At the end of the study period, the scientists concluded that the weight of the monkeys in the normal weight group remained unchanged, while the obese animals lost an important amount of weight – 8.5%, and body fat – 12%, because of an increase in basal metabolic rate.
Neither group had a change in food intake, activity or lean muscle mass.
Judy Cameron, PhD, senior author of the paper and a researcher at the primate center, said that “this study suggests that worries about weight gain with pill use appear to be based more on fiction than on fact.
“Additionally, there may be a differential affect depending on your starting weight – heavier individuals who keep their diet stable may see a weight loss with pill use.
“Most likely, the reason why this belief continues to exist is that the weight gain that seems to occur with age is being attributed to these medications.
“We realize that research in nonhuman primates cannot entirely dismiss the connection between contraceptives and weight gain in humans, but it strongly suggests that women should not be as worried as they previously were.”
Alison Edelman, MD, a physician and researcher in the Department of Obstetrics and Gynecology at OHSU and lead author of the study, said that “a simple Google search will reveal that contraceptives and the possibility that they may cause weight gain is a very highly debated topic.
“Issues surrounding weight are hard to study in humans, and the research thus far has been insufficient to demonstrate whether or not oral contraceptives cause weight gain or loss.
“But this is an extremely important question as concern about weight gain is one of the main reasons why women may avoid or discontinue birth control, which in turn places them at greater risk for an unplanned pregnancy.”
The study results are published online and will appear in next month's edition of the journal Human Reproduction.