How Extended Fasting Affects Testosterone
Let’s talk about how extended fasting affects testosterone. There’s a ton of confusion and fear around this topic. I keep getting comments claiming that extended fasting destroys testosterone or crashes it forever. One person even wrote, you have bodybuilder testosterone, and you decided to kill it! Arguing back with research didn’t help.
So I went with data. I tested my testosterone before my fasts, at the end of a 9-day and a 10-day water fast, and again after refeeding. That gave me a simple, real-life look at what actually happens to testosterone during extended fasting and how fast it rebounds once you start eating again.
⚡ Why This Matters for Health and Hormones
Extended fasting affects much more than just testosterone. During a multi-day fast, the body shifts into a different operating mode that improves inflammation, insulin sensitivity, metabolic flexibility, cellular repair, and overall energy regulation. Many people fast specifically for these benefits.
Testosterone fits into this bigger picture. It influences energy, motivation, muscle retention, mood, and metabolic health, and it naturally declines with age. Levels also respond to sleep, stress, diet quality, alcohol, body fat, and overall lifestyle. Fasting does impact testosterone, but not in the dramatic way people often fear. The drop during fasting is temporary, and it rebounds once refeeding begins.
By the way, if you are interested in learning more about fasting benefits, here’s my research-backed list of benefits 👉 https://fasting.center/benefits
📊 What Research Shows
Research is clear on the short-term pattern
Testosterone drops during extended fasting
It returns to baseline after refeeding
The dip is a normal energy-conservation response, and free testosterone often falls more because insulin drops and SHBG temporarily rises. What’s often overlooked is the long-term effect. Extended fasting can actually support healthier testosterone levels over time by improving the systems that regulate hormones. Fasting-refeeding cycles have been shown to improve insulin sensitivity, reduce visceral fat, lower inflammation, and enhance metabolic health overall. All of these factors are strongly linked to better long-term testosterone regulation.
So while testosterone temporarily decreases during the fast itself, the recovery is reliable, and the long-term metabolic improvements may support stronger hormone balance afterward.
🧪 My Testosterone Data
Below is my complete testosterone data across two extended water fasts. Just for context - I’m not on TRT or any hormone-modifying medications. These are my natural levels.
📉 Total Testosterone
Dec 2024 (before 9-day fast): 969 ng/dL
Feb 2025 (end of 9-day fast): 131 ng/dL
May 2025: 564 ng/dL
Aug 2025 (before 10-day fast): 671 ng/dL
Sep 2025 (end of 10-day fast): 495 ng/dL
Oct 2025 (after refeed): 882 ng/dL
Total testosterone levels before, during and after extended fasts
📈 Free Testosterone
Jun 2023: 9.4 ng/dL
Dec 2024 (before 9-day fast): 10.8 ng/dL
Feb 2025 (end of 9-day fast): 1.5 ng/dL
May 2025: 7.1 ng/dL
Sep 2025 (end of 10-day fast): 5.2 ng/dL
Oct 2025 (after refeed): 10.7 ng/dL
Free testosterone levels before, during and after extended fasts
In both fasts, the pattern is the same: testosterone drops during fasting and rebounds during refeeding. The dip is temporary, and levels go back to normal once you start eating again. And I have no clue why my testosterone is this high. And for some reason, it doesn’t seem to help much with building muscle. Bummer 😊
📘 Final Thoughts
Extended fasting changes many systems in the body, and hormones respond accordingly. Some rise, some fall temporarily, and most return to normal during refeeding. Testosterone follows this same pattern. The dip is expected, and the recovery is reliable.
If you want to see all my fasting data - glucose, ketones, Dexa scans, weight changes, and lean mass trends - here’s the page dedicated to all of it 👉 https://fasting.center/fasting-results