Gym Gains, Baby Pains: The Shocking Side-Effect of Popular Muscle Supplements
Popular supplements used by male athletes and bodybuilders—specifically BCAAs like valine, leucine, and isoleucine—may be quietly reducing their chances of becoming fathers.
A new study shows that these muscle-boosting compounds, especially valine, significantly impair sperm quality and fertility in male mice.
Fertility in Peril: The Supplement Link
A new study published in Zygote, a journal from Cambridge University Press, reveals that popular over-the-counter supplements used by many male athletes and bodybuilders could be affecting their fertility. This finding comes at a time when scientists are increasingly concerned about a worldwide decline in male reproductive health.
The study focused on branched-chain amino acids, or BCAAs, which are commonly taken to boost muscle growth and recovery. In lab tests, male mice given BCAA supplements showed clear signs of reproductive trouble. Their sperm counts dropped, and their overall fertility declined. Among the three main BCAAs—leucine, isoleucine, and valine—valine appeared to have the strongest negative effect on sperm health.
Protein-Rich Diets May Harm Sperm Quality
These early findings raise important questions about human fertility. Many men consume large amounts of animal-based proteins, such as meat and dairy, which are naturally high in BCAAs. In addition, fitness enthusiasts and bodybuilders often take concentrated BCAA powders to enhance performance and muscle mass. According to the researchers, these habits may unintentionally reduce sperm quality and make it harder to conceive.
Lead author Roya Kamali, from the Royan Institute, believes the link between supplement use and male fertility deserves closer attention as “the unrestricted use of dietary supplements for bodybuilding by athletes and consumers in general could be a public health concern. “In bodybuilders in particular, given that the vast majority of these consumers are young men of reproductive age, it is important to study in more detail the impact of such a choice on their ability to have children.”
Implications for Global Fertility Trends
Co-author Joël R. Drevet, from Clermont Auvergne University, said that if the data obtained from an animal model could be confirmed in humans, it could help explain the global decline in male fertility recorded in recent decades, for which environmental factors, including diet, are suggested as major culprits.
Reference: “Supplementation with specific branched-chain amino acids (BCAAs) affects mouse sperm parameters and testicular apoptotic gene expression” by Roya Kamali, Leila Rashki Ghaleno, Amin Izadi, Zahra-Sadat Ghasemi, Vahid Esmaeili, Nima Eila, Adel Pezeshki, Joël R. Drevet, Abdolhossein Shahverdi and AliReza Alizadeh Moghadam Masouleh, 13 May 2025, Zygote.