Women's Bodies As A Research Gap - Part II
20.06.2024
This is a follow-up of the blog post from mid-December 2023, in which I pointed out discrepancies in research between men and women and the implications this has for women. For some reason it has taken me a while to translate this one.
As promised, I will now shed some light on recent findings on women’s health and nutrition. I have focussed in particular on the menstrual cycle, i.e. the healthy woman, young to middle-aged. I have also included commonly associated disorders and discomforts, such as premenstrual syndrome. On the other hand, there is so much information on nutritional interventions for breast or ovarian cancer, for example, that I will leave it out for the time being for reasons of scope.
The 1980s
I found two studies from the 1980s: negative influences of a vegetarian reduction diet on hormone regulation during the menstrual cycle were observed (3). In the other study, conducted a year later, it was observed that a relatively extreme calorie restriction with a vegetarian diet had little influence on the menstrual cycle, whereby differences in age groups were also observed here in particular (5). So all this is still not very meaningful for our research question, and you can see from the studies how different the perception of vegetarian diets, reduction diets and women per se was at the time. I’m seriously questioning whether a study with a prescribed maximum of 1000 kcal per day, as carried out by Schweiger et al. (1987, source 5), would still hold up before the ethics committee today.
Recent studies since 2019
Between the 1980s and the late 2010s there seems to be a relatively big publication gap about this topic. Let me know if you know about a study I’ve missed.
Nowadays, the influence of nutrition on the menstrual cycle is often investigated in connection with professional female athletes. There is, for example, a narrative review (7) from which a few findings can also be derived for general nutritional recommendations. For example, in the follicular phase, i.e. during the days leading up to ovulation, the breakdown of fat and protein is lower and the metabolisation of carbohydrates is proportionally higher. Less carbohydrate is also stored in its storage form glycogen in the liver and muscles. In the second half of the cycle, the luteal phase, the ratios are reversed. More fat and protein is oxidised, more carbohydrate is stored and, due to the slightly higher body temperature, the basal metabolic rate is also slightly higher during this time. The authors summarise „slightly“ being 2.5-11.5% higher in the luteal phase (see Wohlgemuth et al. 2021, p. 6 (7)). One nutritional technique for improving performance that is based on carbohydrates is glycogen supercompensation. This works better in the first half of the cycle when the metabolism is proportionally more carbohydrate-based (see Wohlgemuth et al. 2021, Fig. 2 (7)). This study also reiterates that the body composition of women and men is inherently different, with women having a significantly higher body fat percentage. The study is freely available on the internet and a few exemplary diet plans are also presented.
Just last year, in 2023, Rogan & Black published a narrative review of the existing literature on how the energy intake of women varies along the menstrual cycle in their everyday lives. The result: it is poorly researched and more research is needed. Of course, it is not possible to make precise statements anyway; the individual situation and body composition must always be taken into account. However, the intake of more calories in the first half of the cycle is confirmed here. There is talk of up to 10 kcal/kg more fat-free body mass. Specifically, this means 159 to 529 calories per day. (4).
About the premenstrual syndrome
Premenstrual syndrome (PMS) affects a relatively large number of women. Here too, the question naturally arises as to whether nutrition has an effect. Short answer: nutrition actually plays a role in everything health related. For example, ensuring an adequate intake of vitamin D and calcium during PMS may reduce symptoms (1). Overall, however, a review by Siminiuc and Turcanu from last year (2023) concluded that the research situation on this topic is extremely poor. Certain minerals and vitamins could have positive effects, but they usually do anyway. In general, there is a fairly large research gap here. These two authors also emphasise that nutrition definitely has a role to play in alleviating PMS symptoms, but hardly anyone has done any research into exactly which ones and how we can take targeted action to alleviate our symptoms (6).
The influence of a low-carb diet and the traditional Mediterranean diet on polycystic ovary syndrome (PCOS) was investigated in a small study. The results should be seen as preliminary and only overweight patients were examined. However, there are hopeful results that in this prospective study, both diets improved some of the health indicators that are representative of fertility and cycle regularity compared to the initial state (2). A question came to mind, since the „Mediterranean diet“ is simply a wholefood, high-fibre and fresh diet (I should probably write a blog post about this next time so that you can get a better idea of what it means, because in nutritional science, Mediterranean cuisine is not pizza or bifteki) – to what extent does switching to a wholefood diet simply improve overall health?
Conclusion: there is much research yet to be done
Overall, this is a pretty frustrating research topic. Just about every study I’ve read on this topic starts with some variation of „many women are affected, the topic is poorly researched“ and some reviews draw this conclusion again after analysing the existing literature. The situation looks a little better with cycle-adapted training plans, i.e. when it comes to adapting the sports programme. In other words, from a nutritional science perspective, I can currently draw no other conclusion than „many women are affected, but the issues are not particularly well researched“. What is relatively „certain“ is a higher calorie requirement in the second half of the cycle and an increased focus on fat and protein loss compared to the first half.
(1) Abdi F, Ozgoli G, Rahnemaie FS. A systematic review of the role of vitamin D and calcium in premenstrual syndrome. Obstet Gynecol Sci. 2019 Mar;62(2):73-86. doi: 10.5468/ogs.2019.62.2.73. Epub 2019 Feb 25. Erratum in: Obstet Gynecol Sci. 2020 Mar;63(2):213. PMID: 30918875; PMCID: PMC6422848.
(2) Mei S, Ding J, Wang K, Ni Z, Yu J. Mediterranean Diet Combined With a Low-Carbohydrate Dietary Pattern in the Treatment of Overweight Polycystic Ovary Syndrome Patients. Front Nutr. 2022 Apr 4;9:876620. doi: 10.3389/fnut.2022.876620. PMID: 35445067; PMCID: PMC9014200.
(3) Pirke KM, Schweiger U, Laessle R, Dickhaut B, Schweiger M, Waechtler M. Dieting influences the menstrual cycle: vegetarian versus nonvegetarian diet. Fertil Steril. 1986 Dec;46(6):1083-8. PMID: 3096794.
(4) Rogan MM, Black KE. Dietary energy intake across the menstrual cycle: a narrative review. Nutr Rev. 2023 Jun 9;81(7):869-886. doi: 10.1093/nutrit/nuac094. PMID: 36367830; PMCID: PMC10251302.
(5) Schweiger U, Laessle R, Pfister H, Hoehl C, Schwingenschloegel M, Schweiger M, Pirke KM. Diet-induced menstrual irregularities: effects of age and weight loss. Fertil Steril. 1987 Nov;48(5):746-51. doi: 10.1016/s0015-0282(16)59523-5. PMID: 3117591.
(6) Siminiuc R, Ţurcanu D. Impact of nutritional diet therapy on premenstrual syndrome. Front Nutr. 2023 Feb 1;10:1079417. doi: 10.3389/fnut.2023.1079417. PMID: 36819682; PMCID: PMC9928757.
(7) Wohlgemuth KJ, Arieta LR, Brewer GJ, Hoselton AL, Gould LM, Smith-Ryan AE. Sex differences and considerations for female specific nutritional strategies: a narrative review. J Int Soc Sports Nutr. 2021 Apr 1;18(1):27. doi: 10.1186/s12970-021-00422-8. PMID: 33794937; PMCID: PMC8015182.
