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It doesn’t take much. A single study is published showing that when healthy subjects lift weights and add a whey protein supplement to their diet, the normal increase in testosterone produced by the first is blunted by the second. Next thing you know, headlines similar to mine (“Whey protein lowers testosterone!”) are popping up all over the Internet and consumers get concerned. More often than not, the concerns are unwarranted, as appears to be the case this time.

Juha Hulmi, PhD, is a researcher at the University of Jyväskylä in Finland with whom I have corresponded in the recent past. In a study published in the Journal of Steroid Biochemistry & Molecular Biology, Hulmi and colleagues attempted to determine whether or not feeding whey protein to older men (~62 yrs) before and after a single bout of resistance exercise could affect testosterone.

The subjects in Hulmi et al.’s study (1) performed 5 sets of 10 reps of leg presses, with 2 minutes of rest between sets. Before (pre-) and after the (post-) workout, the subjects received either 250 ml of whey protein isolate (supplying 15 g of protein) or a non-caloric placebo that looked and tasted pretty much identical. The result: Whereas lifting weights caused testosterone levels to increase in subjects who received the placebo, those consuming whey experienced a decrease in both serum total and free testosterone levels, similar to what the scientists later observed in a study involving younger men (2).

This diagram shows the effect of consuming whey vs. a placebo before and after lifting weights on free testosterone levels.

Curious if the observed fall in testosterone observed might be sufficient to affect muscle mass, I decided to ask Hulmi. My questions were as follows:

(1) Is it conceivable that the reduction in testosterone you observed with whey consumption might be sufficient to blunt resistance exercise-induced increases in muscle size if repeated over the long-term?

(2) Do you have any reason to believe that it was the pre- as opposed to post-workout consumption of protein that reduced testosterone levels, or vice versa?

Below is his response. Note that I have edited it slightly for the sake of clarity. Dr. Hulmi is Finnish.

Hi, Rob. I believe that the blunting of testosterone is a homeostatic response and its meaning may be close to zero. See (attached) my recent paper in which the consumption of whey protein increased muscle size measured by MRI showing that protein increases muscle mass even when the subject’s “normal” protein intake is pretty high, and even when the testosterone response to resistance exercise is a little bit blunted (not shown). BUT, I believe also that TOO much protein is not good either, as correlational studies suggest: http://www.ncbi.nlm.nih.gov/pubmed/15532008.

In answer to your second question, it is not just pre-workout consumption of protein that affects testosterone: http://www.ncbi.nlm.nih.gov/pubmed/8175597

BUT as I said, it seems that exercise-induced hormonal responses may be a little bit overrated: http://www.ncbi.nlm.nih.gov/pubmed/19910330

SO, you should forget hormonal responses and look, for example, at how protein affects on mTOR signaling such as in my paper: http://www.ncbi.nlm.nih.gov/pubmed/19299575

In summary, post-workout consumption of protein is good but nothing spectacular will happen. ;)

1. J Steroid Biochem Mol Biol. 2008 May;110(1-2):130-7.
2. http://jap.physiology.org/content/106/5/1720.long