Why did Fasting Double my Testosterone?

I presented my 5 day fast blood results on Youtube, but I didn't talk about what happened after that.

I just released a video on my channel titled I Fasted for 5 Days and Walked 7 Hours a Day. There I talked about how the benefits of exercise, cold exposure and fasting synergize. I got my blood tested around 1PM on the first day shortly after I finished my last meal and I got it tested again 120 hours later again at 1PM after 5 days of fasting. Here were my blood results before and after:

LDL Cholesterol 125 mg/dl ⇨ 101mg/dl
HDL Cholesterol 40mg/dl ⇨ 43mg/dl
Triglyceride 56mg/dl⇨ 39mg/dl
Insulin 4.5 mcu/ml ⇨ 1.5 mcu/ml
White Blood Cells 6720 ⇨ 4060
CRP 0.25mg/dl ⇨ 0.14mg/dl
IGF-1 194ng/ml ⇨ 111ng/ml

All in all, this was a quite good result. Per this paper, a reduction in White Blood Cells may indicate that more autophagy was going on. CRP reduction indicates less inflammation and as explained in the video, a reduction in IGF-1 should have a longevity benefit. However some may argue that if you’re aiming to build muscle, you want to have more IGF-1. (We’ll address that later)

What I didn’t mention is that I got my testosterone checked at the start of the fast. A couple months earlier it was 802.1ng/dl, but when I got it checked at the start of this fast it was 421.5ng/dl. This was still in the normal range and my libido, strength, mood et cetera were all doing just fine so I wasn’t too worried …but also not happy that it’s lower than before. It’s hard to say if it was due to the fasting or just that I was so busy walking the whole day that I didn’t have much time to think about sex, but I didn’t have much libido during the fast. I was expecting the multiple day fast to drop my testosterone, so I was surprised when I got the result on the last day of fasting before eating my meal: 424.8ng/dl. Basically no change.

Testosterone 421.5ng/dl ⇨ 424.8ng/dl

I also got my blood checked six days after I started eating normally again. To keep the time consistent, I got all three blood tests at 1PM. This is where things got really interesting.

My testosterone was now 887.1ng/dl, more than double what it was. I was just 37 points away from being above the reference range.

Actually, I was aware of this phenomenon before I got these results. While doing research for my video What happens if you Don’t Eat for 44 Days? 11 months ago, I came across this 1980 paper titled Reproductive Function during Fasting in Men where they had men fast for 10 days and then refeed for 5 days.

As you can see, 4 of the men experienced a steady decline in testosterone over the fast, but then their testosterone shot up above baseline after refeeding. One man doubled his testosterone from 800ng/dl to 1600ng/dl.

So what the hell is going on?