A new study from researchers at the Murdoch Children’s Research Institute (MCRI) in Melbourne and the University of Melbourne has found that feminizing gender-affirming hormone therapy (GAHT) doesn’t just change outward traits. It rewires protein composition in the blood to align more closely with a person’s gender identity.
What the Study Found
The research team examined 40 adult trans women at Austin Hospital, each undergoing common feminizing hormone therapies. They measured levels of more than 5,000 different blood proteins before treatment and again after six months.
They then compared those changes with data from over 55,000 participants in the UK Biobank to see how these proteins typically differ between cisgender women and cisgender men.
The headline result showed that seven out of ten key proteins that normally differ between cis men and cis women shifted significantly after six months of hormone therapy in the trans women participants. The shift was toward the female pattern.
Specifically, proteins tied to male reproductive function and fertility decreased, while those associated with breast development, body fat distribution, immune function, and cardiovascular health increased. These changes mirror what is seen in women undergoing hormone replacement therapy for menopause.
RELATED: Study Links Hormone Therapy to Heart Marker Changes
Why It Matters
For transgender people, this research has profound meaning. It shows that hormone therapy doesn’t just create external changes. It alters the body’s biology in measurable ways.
This matters for two main reasons:
- Biological alignment: The study gives scientific backing to what many transgender people already experience. Hormone therapy helps the body feel right at a deep level. The findings show that internal biochemistry shifts toward one’s gender identity, not just external presentation.
- Health monitoring and personalization: Because these proteomic changes can be measured, healthcare providers can develop more individualized treatment plans. MCRI Associate Professor Boris Novakovic noted that these changes may influence the risk of allergic and autoimmune diseases, which are more common in females, but may reduce the risk of heart disease, which is more common in males.
Meanwhile, Professor Ada Cheung of the University of Melbourne explained that studying proteins could help develop personalized treatment approaches, monitor the effectiveness of gender-affirming hormone therapy, and allow for early detection of potential side effects on heart health or immune function.
Looking Ahead
While this study is small, with only 40 participants, and focuses on the first six months of treatment, it establishes an important precedent. Future research will be needed to track how sustained hormone therapy affects proteins and related health outcomes over time.
It also raises important clinical questions. Should transgender people on hormone therapy have different screening protocols for heart health and autoimmune conditions? Can specific proteins act as biomarkers to guide hormone dosing? How might these results vary across trans men, nonbinary people, and those using different regimens?
The Bottom Line
This study is a major step forward for transgender healthcare. It provides scientific validation that gender-affirming hormone therapy reshapes the body’s biology to better reflect identity. For many transgender individuals, that is more than science; it is recognition. The body is capable of incredible adaptation, and for trans people, it means that who they are is written not only in their reflection but within their biology too.
