Does soy lower testosterone?

No. For normal human intake, soy does not lower testosterone or raise oestrogen in any meaningful way. This is one of the most stubborn myths in men's health, and the evidence is now clear.

The worry comes from isoflavones, plant compounds in soy that can weakly attach to oestrogen receptors. On paper that sounds alarming, but the most thorough analysis, a large review pooling dozens of studies, found that soy and isoflavones had no significant effect on men's testosterone or oestrogen. The handful of scare stories that circulate, such as the man who drank enormous quantities of soy milk every day, involve intakes far beyond anything normal.

In realistic amounts, soy is simply a high-quality protein with a good nutritional profile:

• Tofu, edamame, tempeh and soy milk as part of a normal diet sit well within the safe range
• Swapping some processed and red meat for soy tends to help your heart and your waistline
• A leaner, healthier body composition supports testosterone rather than harming it

So the practical effect of soy, if anything, runs in your favour. It belongs in the same category as the other overblown food fears covered in what foods lower testosterone: a distraction from the things that actually matter.

It is worth understanding why the fear took hold. Isoflavones are called phytoestrogens, which sounds like "oestrogen", but they are far weaker than the real hormone and can act in either direction depending on the tissue. In men eating ordinary amounts, the net effect on hormones is negligible, which is precisely what the large pooled reviews found.

What to do: eat soy without worrying about your testosterone. If your levels are low, the real levers are sleep, body fat, training and correcting deficiencies, set out in raising testosterone naturally, not avoiding tofu. Spend your energy there, not on a myth.

Go deeper: read the full profile of soy, tofu and edamame in the food library.