Millions of women around the world experience premenstrual syndrome (PMS), characterized by physical and psychological symptoms such as irritability, anger, depressive mood swings, pain and bloating in the weeks leading up to the normal monthly menstrual cycle.
Symptoms of PMS may be severe enough to result in athletic impairment, posing a huge hurdle for prospective female athletes that may be out of commission for an extended period of time each month.
A study was devised to investigate the relationship between dietary protein consumption and occurrence of PMS.
Researchers at Kindai University in Japan recruited 135 female athletes between the ages of 18 and 23 years, who are members of authorized university clubs that consistently produce highly ranked Japanese athletes amongst university sports disciplines.
Part of the study involved completion of self-administered questionnaires that ascertained normal dietary habits, demographics and if it was usual for that individual to experience PMS related athletic impairment of performance.
Total protein from animal and plant sources was then calculated, along with the relative proportion of each in the diet. After which, participants were divided into two groups; one group that included 18 athletes with self-reported PMS related performance impairment, and 117 subjects that did not experience such impairment.
Consideration was also given to the amount of time spent training daily, along with average caloric intake.
Overall, very small difference was observed in the total amount of protein consumed daily by the athletes. In particular, however, was the fact that the group that experienced performance impairment as a result of PMS had self-reported higher intake of animal-based proteins, relative to the amount of plant proteins consumed (average 50g vs 25g).
The group whose performance was unaffected reported an average animal protein consumption of 35 g, versus 27 g of plant protein daily.
Calculating the relative proportion of plant protein in both groups, the women that experienced PMS induced performance impairment consumed 39% of their protein from plant-based sources, while the unaffected group consumed an average 46% plant-based protein .
Even though there was a clear correlation between the relative amount of plant protein consumed and occurrence of PMS related performance impairment, the sample size of the study is very small and not enough to make generalizations.
For instance, Asians typically consume a greater amount of plant-based proteins than their Western counterparts, which would mandate inclusion of a wider cross-section of women in subsequent studies.
In addition to this, analysis of the particular plant proteins consumed need to be considered, since soy proteins, for example, contain phytoestrogens  that may influence hormonal homeostasis at this time. Other protein sources such as pea protein are well-accepted, and warrant inclusion in additional studies too.
In addition to this, the stress physical activity places on the body could have also contributed to differences within the two groups, as inflammatory processes that occur post training could contribute to greater pain (and prostaglandin synthesis).
Regardless, this preliminary study has paved the way for subsequent studies of a similar nature to be conducted, using more variables and better controls.
Yamada K, Takeda T (2018). Low Proportion of Dietary Plant Protein among Athletes with Premenstrual Syndrome-Related Performance Impairment. The Tohoku Journal of Experimental Medicine 2018 Feb; 244(2):119-122. doi: 10.1620/tjem.244.119.
Bryant M, Cassidy A, et al. Effect of consumption of soy isoflavones on behavioural, somatic and affective symptoms in women with premenstrual syndrome. The British Journal Of Nutrition 2005 May; 93(5):731-9.