How "The Pill" Impacts Metabolism

As of last year, roughly 2 out of 3 Irish women aged 18-45 used a method of contraception. Therefore, it's of interest to us to investigate how this might impact metabolism and body composition. First, we need to understand a little bit about this method of contraception.

Very often, we speak of "the pill" as being synonymous with contraception for women, but this is, of course, not the case. Contraceptive methods available for use include:

• Combined and progestin-only pills
• Implants, patches, injections, vaginal rings, hormonal intrauterine devices IUD.

The oral contraceptive pill (OCP) is the most common method, and particularly the combined oral contraceptive pill (COCP i.e. estrogen + progesterone). There are 4 generations of progestins used, with the 3rd + 4th exhibiting fewer side effects and less androgenicity.

1st Gen e.g. Norethisterone
2nd Gen e.g. Levonorgestrel
3rd Gen e.g. Norgestimate
4th Gen e.g. Drospirenone

How does the pill work?

It works via suppression of ovulation by inhibiting the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus, suppressing luteinising hormone (LH), follicle-stimulating hormone (FSH), and specifically the LH surge mid-cycle. This results in suppressed folliculogenesis, atrophy of the endometrium and thickened cervical mucus. Therefore, conception is mostly (see below) prevented from occurring.

With that out of the way, it's reasonable to assume that such hormonal manipulation might impact metabolism and body composition. After all, this is almost the female equivalent of using "steroids" (e.g. testosterone), and there is certainly no shortage of anecdotes from women who claim the pill impacted their body weight. In fact, concerns about weight gain are one of the leading reasons for discontinuation of the OCP, and perceptions of weight gain often do not match their true body weight.

Firstly, there are methods of hormonal contraception that can precipitate weight gain, particularly earlier generation pills and depot medroxyprogesterone acetate (DMPA). Therefore, the answer to the question does hormonal contraception contribute to weight gain? is yes, sometimes, but not with the most frequently used methods. 

The overall body of research as it currently stands suggests that the COCP and progestin-only pill (POP) are at the very least neutral for body composition (neither benefit nor harm) overall, and thus claims that they cause weight gain don't seem to be well supported (that doesn't mean this may not be the case for some women, as responses vary in terms of appetite, cravings, water retention, etc.). The data overall are relatively limited, and there has been some recent evidence to suggest that women on the COCP may regain more weight following weight loss, but this study had limitations (asymmetry in sample size, considerable variation in rates of weight regain, and more). Other studies demonstrate greater weight loss during caloric restriction in COCP users vs non-users, but this data is limited. 

For an advanced overview of the effects on metabolism, please refer to this review paper.
 

In summary, as it stands currently, I consider the COCP to be a neutral contributor to body composition, and this is not something I view as being a limiting or enhancing factor to the progress of our female clients at Triage. Individual responses vary, and for some women, it may be positive, and for others, it may be negative. For most, it's probably not something that is worthy of much concern [for body composition].

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Gary McGowan

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