Does this birth control make me look fat: The effects of progesterone-only contraception on metabolism

by: Stephanie Gates

Weight gain has been a self-diagnosed side effect of many methods of birth control for years. While this has not been proven, scientists have found many associations between progesterone, an endogenous hormone commonly used in female contraception, and resting metabolic rate. This association might, in turn, lead to an increase in appetite and overeating. A study conducted by the Department of Obstetrics and Gynecology at Duke University looked at this association more closely to determine exactly how birth control affects the resting metabolic rate. 

To test the correlation, researchers looked at the progesterone-only birth control, depot-medroxyprogesterone acetate, otherwise known as Depo-Provera. This one-time release form of contraception is given as a shot once every three months. The team of researchers expected an increased resting metabolic rate in girls who used the Depo-Provera method of contraception, meaning an increased resting metabolic rate due to the increase in progesterone.

The researcher’s hypothesis came from assumed information about resting metabolic rate and the female menstrual cycle. There have been several studies showing an increased resting metabolic rate during the luteal phase, the latter phase of the cycle. This phase has shown to correspond to elevated progesterone levels. There are also certain periods during the second and third trimester of pregnancy when women tend to have increased metabolic rates, and this happens to be a time with higher levels of progesterone in the body. While there is no definitive link between increased progesterone and increased metabolic rate, the researchers observed those trends in the female menstrual cycle and hypothesized that increased progesterone might cause increased metabolic rate. 

For the study, the researchers needed a method of controlling the release of progesterone in opposition to the body’s natural release. A progesterone-only birth control was the perfect method, as it only involves one administration of a tested, safe, and commonly used drug.

The study looked at twenty-two healthy women between 18 and 35 years old with a healthy body mass index (BMI), a measure of weight-to-height ratio.  Women who had used long-acting hormonal or oral contraception in the last nine months were excluded from the study because their beginning metabolic rate might have been affected by hormones in previous contraceptive methods. Thirteen of the twenty-two women completed all three sessions of the study. The women were measured at injection, at three weeks, and at nine weeks for several factors. They were first measured on the change in resting metabolic rate from the first week to the third week and then to the ninth week. They were also measured for changes in body composition, a lean mass to fat mass ratio, as this would determine if the progesterone also caused changes in body mass. Their body temperature, body weight, BMI, blood pressure, and pulse were measured as well. 

There was no observed change in BMI during the study. There was, however, an increase in body temperature at the third week that supported the discovered increase in resting metabolic rate. There was also no change in lean or fat body mass. From these results, the researchers found that there is an independent effect of progesterone on resting metabolic rate which may indirectly affect weight gain. The researchers hypothesize that an increase in resting metabolic rate might cause an increase in appetite. If not managed properly, the increase in appetite could potentially lead to weight gain. It is important to note that the birth control itself, and the hormone used in it, does not directly cause weight gain; it is the change in eating habits, which are within the women’s control, that may cause changes in weight. 

It is important to examine all possible side-effects when choosing a birth control method and to choose a method that fits best with your body and lifestyle. This research indicates that women can choose progesterone-only methods of contraception and they will not gain weight directly from taking it. Rather, these women can choose to be conscious of their eating habits if they wish to maintain their current weight.

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