Claims that oral contraceptive pills encourage weight gain are false, researchers from the Oregon National Primate Research Center at Oregon Health & Science University wrote in the medical journal Human Reproduction.
Lead author, Alison Edelman, M.D., said:
"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 researchers spent nearly a year studying some rhesus macaque monkeys at their Oregon National Primate Research Center (OHSU). A rhesus monkey's reproductive system is almost the same as a human's. With monkeys a wider range of variables can be more closely gauged and controlled, such as exactly what they are eating, when and how much.
Half of the monkeys were normal weight while the other half were obese when the study began. They were given oral contraceptive doses according to their body weights, matching human equivalents as closely as possible. They were treated for eight months. They gathered data on the animals' nutritional intake, levels of physical activity, lean muscle mass, and body fat mass.
They found that:
- The monkeys with normal weight remained the same
- The obese ones lost an average of 8.5% of their body weight
- The obese ones lost 12% of their body fat as a result of a higher basal metabolic rate
- No changes were observed in lean muscle mass, physical activity
"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."
"Combined oral contraceptives and body weight: do oral contraceptives cause weight gain? A primate model"
A. Edelman, J.T. Jensen, M. Bulechowsky and J. Cameron
Hum. Reprod. (2011) 26 (2): 330-336. doi: 10.1093/humrep/deq335
Written by Christian Nordqvist