Intermittent fasting’s effect on testosterone levels

To fast or not to fast?!

Again that scary question, “What will it do to my testosterone levels?

Research is inconclusive and people are biased, so what should I do and who should I believe?

Here are 3 things to keep in mind:

  1. Fact: Fasting lowers testosterone and eating helps to maintain high levels.
    Application: Thus intermittent fasting should not increase or lower total daily testosterone, because the fast is broken daily. Testosterone might decrease or increase more than usual over the course of the day, but not lower the total amount produced each day.
  2. Fact: Chronic gut irritation and an excess of endotoxin producing gut bacteria will poison the body which will create inflammation and lower steroidogenesis every time you eat.
    Application: When you fast, you lower endotoxins and inflammation which will allow the testes to function optimally and produce maximal amounts of testosterone when you do eat again.
  3. Fact: Total calorie intake determines total testosterone levels. A deficit lowers it and a surplus can help increase it.
    Application: If you don’t want to lower your testosterone levels, don’t go in a deficit.

Let’s get to the research.

This study (R) that was better designed than most other intermittent fasting studies, found that testosterone levels were reduced after 8 weeks of an intermittent fasting protocol (16 hour fast / 8 hour feeding window).


Nowhere in the study does it specify when the measurements were taken, and we know from other studies, for instance, when dinner was skipped by one group, they had lower testosterone levels the next morning than the group that didn’t skip dinner (could be because they ate less calories for that day and that lowered their T, instead of the fast negatively influencing their T). So it makes their finding hard to interpret.

If we look at the diurnal rhythm of testosterone, we’ll see that it’s highest in the morning and drops during the day, and then rises again at night.

Diural variation in testosterone

When no food is eaten for breakfast, T will drop more compared to the group that ate.

But what would happen when they refeed? Would they get an overshoot in testosterone? Most probably.

Testosterone after a fastFrom this study (R) we know that after a fast (in this case 10 days), testosterone shot up incredibly during the refeed (which was only 1500 calories, so not really a refeed) and stayed elevated for 4 days.

As testosterone decreased during the fast, their LH increased as well as the LH responsiveness to LHRH.

This study also shows that short term fasting increased the GnRH-elicited LH response by 67% and the corresponding testosterone response by 180% (R).

So during fasting, you get a tradeoff between testosterone and signalling sensitivity. Lower T, but greater sensitivity. Then when you refeed you possibly get a testosterone production overshoot.

Will this enhance muscle growth? Possibly not, as the study by Moro et al (16 hour fast, 8 hour refeed window) found that that fasting and non-fasting group gain equal amounts of muscle.

Perhaps you can optimize this response in your favour by changing when and what you eat as well as when you train.

Charles Poliquin, a famous strength coach, mentioned that cortisol blockers were all the rage a while ago, but when people used them pre-workout, they reduced their hypertrophy gains. But when they used the blockers post-workout, their gains improved. It would seem that the cortisol response from a workout is very important for adaption, but should be blocked immediately afterwards, to promote hypertrophy.

The way we can make the most of this cortisol response while doing intermittent fasting while retaining our boost in androgen sensitivity is to use only BCAAs (5-10g) before workout and then eat a big meal with protein (>40g) and carbs (>100g) after the workout. This will possibly cause a total and free testosterone overshoot while lowering cortisol post-workout, and all that T will be taken up in the muscles for hypertrophy.

If you don’t want to boost cortisol production purposefully pre-workout, like me, you can rather eat a meal with protein and carbs beforehand, enjoy the surges of testosterone and then lift an hour or two later. After the workout, eat another big meal. Both the pre-workout and post-workout meal should be high in protein and carbs and low in fat. This way your total and free testosterone levels are elevated pre-workout (a high carb meal lowers SHBG), which will be ready to flood the muscles during and after your workout to enhance hypertrophy.


There has been no conclusive research done to date that shows that fasting lowers or increases testosterone or have a meaningful effect on muscle growth.

If intermittent fasting works for you and you do feel better on it, definitely give it a go. Some areas where intermittent fasting shines for me is that it 1) frees up time so that I can focus and be creative in the morning, 2) speeds up fat loss compared to not doing it, 3) reduces my hunger when I’m not eating and 4) gives my gut a break from digesting and so on.

Tips to optimize intermittent fast:

  • Use a little EAA (Amazon)(iHerb) during the fast (8-10 hours in) if you’re scared you might lose some muscle.
  • Use HMB (Amazon)(iHerb) – potent anti-catabolic metabolite of leucine
  • Use tribulus terrestris (Amazon)(iHerb) and/or DHEA (Amazon)(iHerb). Both keeps excess cortisol in check and increases androgen receptors. Only androgen receptors correlate positively with hypertrophy, and not total testosterone. Taking DHEA before bed will help with the increase in growth hormone at night.
  • Take a LH boosting supplement, such as maca, during the fast to amplify the testosterone overshoot after the first meal.

Intermittent fasting is just one tool you can use to improve your well-being and speed up fat loss. Proper foods, supplements and exercise are even more important when it comes to optimizing your physique, strength and functionality. Doing it right is really not hard and actually very enjoyable, especially when your mood and energy shoots through the roof. 

I really enjoying doing intermittent fasting and respond really well to it in terms of fat loss.

Want more awesome content like this?

Success! You're on the list.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.