Weight Gain from Birth Control may be influenced by Genes

According to a study conducted by researchers at the University of Colorado Anschutz Medical Campus, a woman’s genetic make-up may cause her to gain weight when using a popular form of birth control.

The strength of the genetic influence on weight disorders varies greatly between individuals. According to research, genes account for only 25% of the predisposition to be overweight in some people, while for others, the genetic influence is as high as 70% to 80%. Knowing how much of a role genes play in your weight may be useful in treating your weight problems.

“For years, women have claimed that birth control causes weight gain, but many doctors have failed to take them seriously,” said Aaron Lazorwitz, MD, assistant professor of Obstetrics/Gynecology and Family Planning at the University of Colorado School of Medicine. “Now, we’ve looked at the genetics and discovered that the way genes interact with certain hormones in birth control may help explain why some women gain more weight than others.”

Some women mistakenly believe that using contraception will make it difficult for them to become pregnant once they stop using it, especially if they are using long-acting reversible contraception (LARC), such as IUDs or the arm implant. Many studies found that some participants lost weight while on the pill, while others gained a few pounds. Weight gain is one of the side effects that cannot be generalized to everyone. However, while on birth control pills, it is preferable to maintain a healthy diet and exercise routine.

For years, women have claimed that birth control causes weight gain, but many doctors have failed to take them seriously. Now, we’ve looked at genetics and discovered that the way genes interact with certain hormones in birth control may help explain why some women gain more weight than others.

Aaron Lazorwitz

The study, which was published online in the journal Contraception, focused on the etonogestrel contraceptive implant. The rod-shaped implant is inserted beneath the skin and contains etonogestrel, a type of progestin that inhibits ovulation.

The researchers examined medical records to calculate weight changes from the time the implant was inserted to the time the women enrolled in the study. They discovered a median weight change of +3.2 kg or about 7 pounds gained over an average of 27 months of use in 276 ethnically diverse subjects. The majority of subjects, 73.9 percent, gained weight.

Genes may play a role in weight gain from birth control

Lazorwitz and his colleagues investigated the genetics of the participants and how they might interact with the birth control drug within the implant using pharmacogenomics, the study of how genes affect a person’s response to drugs.

They hypothesized that variants in genes encoding proteins that degrade and interact with progestin and estrogen hormones could be the key. Finally, they discovered that genetic variants in estrogen receptor 1 (ESR1) were linked to clinically significant weight gain in some study participants.

ESR1 is located on chromosome 6. When activated, it encodes an estrogen receptor that participates in cellular hormone binding and DNA transcription. Previous research has discovered links between ESR1 genetic variants and how well other medications work.

When compared to the other women in the study, women who had two copies of the ESR1 rs9340799 variant gained over 30 pounds more while using the contraceptive implant. The study focused on the etonogestrel contraceptive implant, but other birth control medications may have similar interactions with genes that cause weight gain.

“It’s critical to understand how individual genetic variation influences a woman’s risk of adverse weight gain while using exogenous steroid hormone medications,” Lazorwitz said. For the time being, it is impossible to predict who will be affected. Health care providers can counsel patients about potential weight gain or recommend other forms of birth control, such as copper IUDs, which do not contain hormones.

“As our understanding of pharmacogenomics in women’s health expands,” Lazorwitz said, “we can develop individualized counseling that may reduce the incidence of hormone-related adverse effects, improve patient satisfaction, and help prevent future health risks associated with weight gain.”

If you’ve been overweight for most of your life and haven’t been successful with weight management through consistent diet and exercise, your genes may have a significant impact on your weight. If you have a blood relative or a parent who is also overweight, there’s a good chance your weight is a genetic issue — and this likelihood increases if both of your parents are overweight.