T Nation

Effects of 24-36 Hour Fasts on Testosterone?

How does having 1 or 2 full day fasts per week affect testosterone levels? Is intermittent fasting also recommended with other days of the week?

Here’s a study showing a 180% increase in testosterone from intermittent fasting:


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OP, keep in mind that this result cameabout after a 56 hour non-stop fast, not two 24 hours fasts spread out

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Thanks for the clarification j4gga2!

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I’ve done a bit of fasting but it was before trt. I want to do some more fasting but I am worried about what it will do to my metabolism or anything else whilst I’m on trt.

Is fasting safe on trt?

Consult your endocrinologist

While the study shows some support for the idea of fasting to raise testosterone, I will add a few comments on the design and results and definitions.

First, I.F., as the term was originally coined was about fasting for long periods of a day, up to about 24 hours. Autophagy starts to shut down if you start to make ketones because ketones replace the glucose that is produced from autophagy. A fast of over 24 hours would not fit the “classical” definition of I.F. but I am not discounting the potential benefits of intermediate fasts of 24+ hours.

Second, it only raised testosterone in non overfat individuals. It did not raise testosterone in overfat individuals in the study.

Third, fasting tends to reduce the amount of free testosterone versus total testosterone by increasing binding hormone. As a result the fasting may simply bind more test, lowering free test levels and signalling an increase in T production.

Fourth, everything mentioned in the paragraph above also has been shown to occur with general caloric restriction.

Fifth, non-fasting, ie “eating” slightly lowers test and raises free test, so if you make up the calories over time you probably end up in the same place regarding test unless you lose bodyfat, and if you want to lose bodyfat, it doesn’t seem to matter whether you do it by fasting or general calorie restriction. The “purpose” of IF was to elicit autophagy for someone who wants to maintain their bodyweight and composition. If you have to lose fat, losing fat will help your T come up for a variety of reasons.