Endocrine Disruptors and Your Gains: What the Research Says
You're optimising your training. Your plastic gear might be working against you.
Most serious gym-goers know about testosterone. They know it matters for muscle protein synthesis, recovery, body composition, and drive. They track sleep, manage stress, and time their nutrition to support their hormonal environment.
What most of them haven't considered is what their plastic shaker, plastic water bottle, and synthetic gym gear might be contributing to that same hormonal environment.
The answer, based on a growing body of research, isn't reassuring.
What Endocrine Disruptors Actually Are
Endocrine-disrupting chemicals (EDCs) are compounds that interfere with the body's hormone signalling system. They can mimic hormones, block hormone receptors, or disrupt how hormones are produced and metabolised.
BPA and its replacements:
BPA is the most studied and best known, but as covered in an earlier post, most BPA replacements (BPS, BPF) carry structurally similar hormonal activity. Exposure to BPA or its analogues has been associated with disruptions in the ability of adrenal cells to synthesise key hormones, including testosterone and glucocorticoids.⁴
Phthalates:
A separate class of plasticiser chemicals widely used to make plastics flexible. Found in gym bags, synthetic flooring, resistance bands, and many other fitness products. Males in the highest quartile of urinary phthalate metabolite concentrations have been found to have serum testosterone levels around 12% lower than those in low-exposure groups.⁵
The mixture problem:
Studies on exposure to combinations of BPA and phthalates show additive or greater effects on hormone suppression than exposure to either chemical alone.⁶ A gym bag containing multiple plastic items represents exactly this kind of combined exposure environment.
The Testosterone Link
The research is consistent:
Cross-sectional studies have linked BPA exposure to a 10 to 15% decrease in blood testosterone levels in men. Animal models confirm that BPS, the most common BPA replacement, affects testosterone levels through the same endocrine disruption mechanisms.⁵
Cortisol matters too:
EDCs disrupt glucocorticoid production, including cortisol. Cortisol's relationship with training is well understood: in the right amounts it's part of the adaptive stress response, but dysregulation in either direction impairs recovery, body composition, and performance.⁴
The frequency issue:
A gym-goer who trains five days a week and uses a plastic shaker twice daily is interacting with plastic in a food contact context roughly 10 times per week, every week, for years. This isn't a single large exposure event, it's a chronic, low-dose pattern, exactly the exposure profile that hormonal disruption research focuses on.
What This Means Practically
The science on EDCs and human health outcomes is stronger in animal models than in human epidemiological studies, and the research community is appropriately cautious about drawing firm causal lines. What the human data does show is consistent association between elevated plastic chemical exposure and hormonal disruption in the direction that matters most to athletes: lower testosterone, disrupted cortisol, impaired reproductive health markers.
For someone who's already tracking sleep, managing stress, timing nutrition, and thinking carefully about recovery, the question of what their daily plastic contact is contributing to that hormonal environment seems worth asking.
The most practical step available right now is removing the highest-frequency daily plastic contact from their nutrition routine. Not as a cure. As a logical extension of the same approach they're already applying everywhere else.
Sources
- Oxford Academic, Endocrinology, March 2025. "Effects of Endocrine-Disrupting Chemicals on Adrenal Function." Found that exposure to BPA and its analogues (BPS, BPF) disrupts adrenal synthesis of testosterone and glucocorticoids, with effects shown to be additive when chemicals are combined. URL: https://academic.oup.com/endo/article/166/4/bqaf045/8058667
- PMC, 2025. "Endocrine-Disrupting Chemicals and Male Infertility: Mechanisms, Risks, and Regulatory Challenges." Found that males with urinary phthalate concentrations in the highest quartile have testosterone levels around 12% lower than low-exposure groups, and that BPA exposure is linked to a 10-15% decrease in blood testosterone in cross-sectional studies. Confirmed BPS has similar endocrine disruption mechanisms to BPA. URL: https://pmc.ncbi.nlm.nih.gov/articles/PMC12565704/
- ScienceDirect, 2025. "Effects of exposure to endocrine disrupting chemicals on sex steroid hormone levels." Found that rats exposed to both BPA and phthalates had significantly greater suppression of testosterone production than those exposed to either chemical alone, demonstrating additive hormonal disruption from combined plastic chemical exposure. URL: https://www.sciencedirect.com/science/article/abs/pii/S0890623825002497
