Discussing the menstrual cycle on your Instagram is a seemingly fool-proof way to add credibility to your account. Especially if you’re a man, the idea of a man being “brave” enough to discuss a hugely important biological process that impacts 50% of the population is enough to garner you engagement and admiration. However, the biggest issue with discussion of the menstrual cycle on social media is that it’s often just blanket statements with little consideration of the literature.

The menstrual cycle is often spoken of in absolutes – but can we be absolutely sure of anything in female health?

Resting Metabolic Rate (RMR) in a Nutshell

Resting metabolic rate (RMR), or the amount of calories your body uses at rest to carry out the essential life-giving processes can contribute a greatly individual’s Total Daily Energy Expenditure (TDEE). In some cases, it can account for up to 75% of your TDEE ^[1].

As a result, your RMR can play a huge role in energy balance and weight maintenance. There are a wide variety of influences on your RMR including gender (higher in males), muscle mass, bodyweight, age, height, disease processes ^[2] and as many coaches allude to – the menstrual cycle.

This absolute is often touted on social media – you’re hungrier before your period because your metabolic rate goes up in the luteal (pre-menstrual) phase.

This will often lead to coaches saying that females can burn anywhere from 100-500+ calories extra, simply due to the fact your uterus is aflame. Now, I’ve been on social media long enough to question anything and everything I hear a female fat loss coach spout, so let’s get into just how accurate that statement is. The journey to defiance of charlatanism begins with a single Google Scholar search.

Female Hormones & Energy Balance

This section draws heavily on this review article from Davidsen et al. ^[3], which I highly recommend reading for more background information. The menstrual cycle is governed by the hypothalamic-pituitary-gonadal axis, and is regulated by gonadotrophin-releasing hormone (GRH), follicle-stimulating hormones (FSH), luteinizing hormone (LH), progesterone and oestrogen.

During the luteal phase, progesterone peaks and rapidly drops at the onset of menstruation ^[4]. It is hypothesised that progesterone may lead to increased fat storage in humans ^[5], and we may be more sensitive to fat gain in the luteal phase as a result of a natural elevation in progesterone.

A premenstrual increase in energy expenditure may also be due to the elevation of progesterone levels. Progesterone has a thermic effect on the body, which may account for increase metabolism during the luteal phase ^[3].

Now, this requires further study, so please do not consider this gospel in the absence of any direct evidence. As we discussed above, there are interindividual variations in RMR on a day-to-day basis at baseline anyway, which may be in part due to progesterone, or maybe not at all. Let’s get into the evidence.

The Good, The Bad & The Evidence

The basis of the evidence comes in the form of a good old-fashioned meta-analysis from Benton et al. ^[6]. And, the evidence is a little underwhelming. There were 26 full-text articles included in the meta-analysis, with the combined sample size of 318 women. Yup, you read that correctly. 318 women in 26 studies (an average sample size of 12 women per study – YIKES). Considering the authors found that a sample size of 64 was the minimum number of participants to determine effect size of MC on RMR, it’s not ideal. The largest study sample size included in the analysis was n=32. 50% of the studies had sample sizes of n= <10. So, regardless of what the evidence says we are immediately sceptical.

It goes from bad sampling practices to even worse selection methods. No study had a high quality sample selection process, and all studies were high risk of bias for MC and RMR except for one. There was also discrepancy in definitions of cycle phases (some studies just did pre-and post-menstruation, others had the full shebang of follicular, luteal etc) and cycle length, which decreases the generalisability of results.

Care was taken in many studies to exclude oral contraceptive pill users – but don’t really mention whether other forms of contraception were accounted for. Contraceptives like the copper IUD also impact female sex hormone levels ^[7], and certainly should be screened for during these studies.

In addition, as we discussed previously, there are loads of influences on metabolism. Few studies accounted for these confounding factors (e.g. diet, smoking, alcohol, exercise) which is again a major weakness. No study verified or controlled for menstrual cycle phase status, which kind of defeats the purpose.

With little to no faith in the quality of the evidence and our sceptic hat now firmly on, we can get into the findings. The authors found that the menstrual cycle had a small statistically significant effect on RMR during the luteal phase. Indeed, 47% of studies included in the meta-analysis reported an increase in RMR during the luteal phase. However, in the studies with larger sample sizes, there was no difference in RMR between cycle phases.

This meta-analysis perfectly captures just how iffy and challenging it can be to carry out this kind of research. Verifying the MC phase is expensive (requires bloodwork etc) and the sheer volume of confounding variables that need to be accounted for make it a bit of a nightmare to produce high-quality investigations.

Once you become a sceptic, you can’t help but raise an eyebrow at most of the findings from the research. Take this 2022 study of 30 women, which aimed to discern whether RMR differed across the MC in lean vs obese women ^[8]. First of all, body composition was determined by using bioelectrical impedance scanning (lmfao no accuracy no problem bbz). Lean women demonstrated an increase in RMR during the luteal phase, but this did not occur in obese women. No bodyweight changes occurred across the stages of the MC in both groups. Lean women also increased their energy intake, whilst obese women just ate more carbohydrates and not their overall calories. But again, the authors didn’t control for exercise status, and only sampled a single menstrual-cycle.

Rather, as noted by Henry et al. ^[9], RMR is not stable in all women and is highly variable across the cycle, in some cases by up to 11%.

Is There Anything We Can Conclude?

You would be forgiven for finishing the previous section and despairing at the findings (or lack of!). However, there are some interesting take home points:

• Some individuals may experience an increase in RMR around the luteal phase. True, but whether this fluctuation is due to solely female sex-hormone changes is not clear cut.
• Tracking your cycle and symptoms is important. Whilst we do not have a large body of evidence supporting us, your body is the evidence you need. Tracking your cycle and symptoms can help identify patterns. If you notice regular increases in appetite at certain times of the month it just might be cycle-related!
• Don’t believe everything you see on Instagram. Obviously, this goes without saying, especially when it comes to female health, but don’t get your hormonal health information from an influencer with no relevant qualifications. This can create a nocebo effect, where if enough people tell you you’re hungrier before your period, you believe that to be true. Critical thinking is dead in the social media age. It’s also why it’s important to flag misinformation!

So, long story short, you might burn more calories before your period. Or not. Thank God I poured over dozens of articles only to find out the answer is maybe. Love that for me.

References

1. Ravussin E, Lillioja S, Anderson TE et al. (1986) Determinants of 24-hour energy expenditure in man. Methods and results using a respiratory chamber. J Clin Invest 78(6), pp. 1568-1578.
2. McMurray RG, Soares J, Caspersen CJ et al. (2014) Examining Variations of Resting Metabolic Rate of Adults: A Public Health Perspective. Med Sci Sports Exerc 46(7), pp. 1352-1358.
3. Davidsen L, Vistisen B, Astrup A (2007) Impact of the menstrual cycle on determinants of energy balance: A putative role in weight loss attempts. Int J Obes 31, pp. 1777-1785.
4. Maybin JA, Critchley HO (2011) Progesterone: a pivotal hormone at menstruation. J New York Acad Sci 1221(1), pp. 88-97.
5. Kalkhoff RK (1982) Metabolic effects of progesterone. Am J Obstetr Gynecol 142(6), pp. 735-738.
6. Benton MJ, Hutchins AM, Dawes JJ (2020) Effect of menstrual cycle on resting metabolism: A systematic review and meta-analysis. PLoS ONE 15(7).
7. Barbosa I, Bakos O, Olsson SE et al. (1990) Ovarian function during use of a levonorgestrel-releasing IUD. Contraception 42(1), pp. 51-66.   
8. Maury-Sintjago E, Rodgrígues-Fernández A, Parra-Flores J et al. (2022)  Obese Women Have a High Carbohydrate Intake without Changes in the Resting Metabolic Rate in the Luteal Phase. Nutrients 14(10).
9. Henry CJ, Lightowler HJ, Marchini J (2007) Intra-individual variation in resting metabolic rate during the menstrual cycle. Brit J Nutr 89(6).