Whey Protein and Testosterone: Does It Raise or Lower Your Levels?

Walk into any gym and you will hear two opposite claims about whey and testosterone. One camp says a protein shake spikes your testosterone and helps you build muscle through a hormone surge. The other camp worries that whey comes from milk, milk contains traces of hormones, and therefore the shake lowers your testosterone. Both cannot be right, and as it turns out, neither is.

Short answer: whey has little direct effect on your resting testosterone. It does not raise it in any meaningful way, and it does not lower it. The small hormonal blips you see after training are real but minor, and they are not what drives muscle growth. What whey actually does is supply protein, and protein is what builds muscle.

Where the hormone myth comes from

For years the popular model of muscle growth leaned heavily on the post-workout hormone response. The story went that resistance training plus protein raises testosterone, growth hormone and IGF-1, and that this surge then drives gains. It is an appealing picture because it is simple. The problem is that the acute hormone spike after a workout is small, lasts a short time, and has been shown again and again to be a poor predictor of how much muscle a person actually builds.

Whey does play a role in that acute response, but not the dramatic one the myth suggests. Kraemer and colleagues compared soy and whey supplementation around resistance exercise in men. They found that whey was associated with a more favourable, blunted cortisol response at some recovery time points, while soy tended to lower the testosterone response. The headline is that the differences were modest and centred on recovery hormones, not a testosterone boost from whey (PMID: 24015701).

What controlled studies show

When researchers compare protein sources head to head during a real training programme, the testosterone story gets even quieter. A study on protein source and resistance training looked at body composition and sex hormones and found no meaningful differences in total or free testosterone between groups using different protein supplements (PMID: 17908338). The protein helped the training outcomes, but it did not move resting testosterone in one direction or another.

The dairy-lowers-testosterone fear has also been tested directly. A 2024 randomised crossover trial compared dairy milk and soy milk as a recovery drink after resistance exercise in men and found no significant differences in total testosterone, free testosterone or the free testosterone percentage between the two (PMID: 38854281). The traces of hormones in ordinary dairy are far too small to shift a man's circulating testosterone, and whey powder is a processed fraction of milk with even less of that material.

Why the acute spike does not matter much

Even when a workout or a shake nudges testosterone upward for an hour or two, that nudge does not explain hypertrophy. Training studies that track both the hormone response and the actual muscle gain repeatedly find a weak or absent link between the size of the post-exercise hormone spike and the size of the long-term gain. Muscle growth is driven mainly by progressive training and by getting enough total protein across the day. Whey supports the second part of that equation, which is why whey supplementation around resistance training reliably improves lean mass and strength (PMID: 29751507, PMID: 31041966). It earns its place through protein delivery, not hormones.

What actually moves your testosterone

If your goal is healthy testosterone, the levers that matter are not the brand of your shake. They are sleep, body fat, training and overall energy balance. Chronic poor sleep lowers testosterone. Carrying excess body fat lowers it, because fat tissue converts testosterone toward oestrogen. Very aggressive dieting and overtraining can suppress it. Resistance training and staying lean support it.

This is where whey helps indirectly. By making it easier to hit your protein target, whey supports muscle retention during a fat loss phase and helps with satiety, which makes staying lean more achievable. A leaner, well-trained body tends to have healthier testosterone than an under-muscled, over-fat one. The effect runs through body composition, not through the shake itself.

Practical advice

Do not buy whey expecting a testosterone boost, and do not avoid it fearing a testosterone drop. Use it for what it is, a convenient high-quality protein source. Choose a simple concentrate or isolate, mix it with water or milk to taste, and use it to fill the gaps between whole-food meals. Spread your protein across the day rather than loading it all at once.

How much protein you need depends on your body weight, your training and your goal. An intake between 1.6 and 2.2 grams of protein per kilogram of body weight covers muscle building and recovery for most lifters. Our protein calculator works out your daily target and shows how much of it can sensibly come from a shake.

How much whey is sensible

One to two servings a day is plenty for almost everyone. More whey will not raise your testosterone, and stacking shake on shake past your protein target just adds calories. Treat whey as a tool to hit a number, then let training and sleep do the hormonal work.

Conclusion

Whey protein does not meaningfully raise or lower your testosterone. The acute hormone spikes around training are small and do not predict muscle growth. Controlled studies comparing protein sources, and dairy against soy, show no real testosterone effect. What whey does well is deliver protein, which builds muscle and supports a lean physique, and a lean, well-trained body is what actually supports healthy testosterone. Buy whey for the protein, not the hormones.

Sources

• Kraemer WJ, et al. The effects of soy and whey protein supplementation on acute hormonal responses to resistance exercise in men. J Am Coll Nutr. 2013. PMID: 24015701
• Effect of protein source and resistance training on body composition and sex hormones. 2007. PMID: 17908338
• Acute Effects of Dairy or Soy Milk on Sex Hormones Following Resistance Exercise in Males: A Randomized, Crossover Pilot Trial. 2024. PMID: 38854281
• Effects of Whey Protein Supplementation Pre- or Post-Resistance Training on Body Composition and Performance. 2018. PMID: 29751507
• Effect of whey protein supplementation during resistance training sessions on body mass and muscular strength: a meta-analysis. 2019. PMID: 31041966