Oral Contraceptives Associated with Weight Loss

Whether the use of oral contraceptives (OC) results in weight gain has been a continued argument. Many earlier studies, such as the Conchrane review of 42 randomized control trials, have proved that OC pills do not increase body weight. Despite these, there is a general belief among women that OC pills do increase weight, which is the common reason for discontinuing the use of the pill. In the present study, researchers wanted to determine whether use of the pill affects body weight.

In the U.S., almost 49 percent of pregnancies are unintended ones. Discontinuation of the use of OCs is the most common reason for such a high number of unplanned pregnancies. Thirty to 75 percent of women discontinue the use of OCs in the belief that they cause weight gain. However, many of the earlier studies on humans have shown that OCs do not produce weight gain. Obesity, which has become an epidemic now, is essentially because of genetic factors, food habits and lack of physical activity. In all of the earlier studies, which were carried out on humans, it was not possible to control their food habits and physical activity. The researchers of this study analyzed the effects of OCs in monkeys, as their food intake and physical activity could be easily controlled and monitored.

* This study was conducted on two groups of adult female monkeys. In one group, the monkeys were obese; in the other group, they were normal weight.
* For a period of eight months, all the monkeys were given a combination OC, consisting of ethinyl estradiol and levonorgestrel, so that levels of these hormones in their blood were comparable with that in humans taking OCs.
* All the monkeys were fed a standard diet containing the exact amount of calories that they needed.
* The parameters measured before the start of the experiment, at regular times during the experiment and three months after completing the OC therapy included body weight, body fat, physical activity, metabolic rate and blood levels of glucose insulin and leptin.

* There was a decrease of 4.56 percent of body weight in the group of normal monkeys; it was more, 8.58 percent, in the obese monkeys.
* With use of OCs, there was a significant reduction in body fat, from 22.8 to 15 percent. This was also seen more in the obese monkeys.
* The metabolic rate in both the groups was significantly increased, while there was not much change in physical activity.
* “Serum insulin and leptin levels were significantly higher in obese versus the normal BMI animals.”

Next steps/Shortcomings
Not measuring the appetite of monkeys was the main drawback of this study. Also, the food that was supplied to the monkeys was exactly calculated. In practical situations, such restrictions are not possible, especially in humans. There is a possibility that as OCs increase the metabolic rate, they would also increase hunger. This may prompt the woman to eat more, ultimately resulting in obesity. More similar studies are necessary to determine whether giving unlimited food also yields similar results. The second drawback of the present study is that the OCs were given continuously to the monkeys; whereas, humans generally take these pills in cycles of 25 days.

This study proves that use of OCs does not cause obesity or weight gain. On the contrary, they help in decreasing weight. This effect of weight reduction is more pronounced in obese individuals. ”Our results demonstrate that combined OCs increase the basal metabolic rate and result in weight loss due to reduction of body fat but not lean body mass in obese female macaques maintained on stable diet.” The authors say the reason they “found a greater decrease in percent body fat in the obese group was that they had more fat stores available for fuel mobilization.” They point out that body weight is controlled by many physiological systems, which change activity to counteract change in one system, and thereby can slow down weight loss.

For More Information:
Combined Oral Contraceptives and Body Weight: Do Oral Contraceptives Cause Weight Gain? A Primate Model
Human Reproduction, December, 2010
By A Edelman; J T Jensen; Oregon Health and Science University, Portland, Oregon and Division of Reproductive Sciences, Oregon National Primate Research Center, Beaverton, Oregon

*FYI Living Lab Reports Are Summaries of the Original Research.
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