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Hello all.

The meta-analysis on Soy and its effect on testosterone mentions 75mg isoflavone intake and suggests "Neither soy nor isoflavone intake affects male reproductive hormones".

The review cites a study which is one of the 8 studies which seem to look at isoflavone intake > 100mg.

The study suggests the subjects took an additional 120mg to their daily normal diet. It resulted in about 5pc decrease in TT (other study resulted in about 6pc decrease in FT but no effect in TT).

Could anyone help me understand the limitations of this study cited (that with 120mg intake)?

Edit: The subjects were 'omnivores'.

Thanks in advance.

Edited by Amar
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I read the 2003 study from Gardner-Thorpe et al., but couldn't say if there are some strong limitations, maybe 120 mg/d is unrealistic since Asian people consume a high amount of isoflavones which reaches 25 to 50 mg/d. The difference from the control is statistically significant by the method used by the authors, but it may have been less significant by more modern statistical analysis, the TT CI's overlap, and the number of data, n=19 is not very high.

Edited by mccoy
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The study says subjects were omnivores and they had *an additional 120mg* daily, could it be that they already used to have more than that daily in their normal diet?

The thing is soy, as everwhere, here (Asia) is now being used as primary source of protein for vegans. So its quite easy to hit >100mg intake. Protein supplements are kind of heavy on pocket. So, we would mostly be relying on soy (chunks) i.e. TVP if on calorie counting especially if aim is higher protein intake.


Mark Messina's suggestion (which generally might be taken with a pinch of salt due to his funding(?)) is that 100mg is safe upper limit and he seems to suggest that in order that we dont miss out on other good sources of protein (say like legumes/lentils etc).


Does the meta-analysis say 75mg to be safe or did I miss something? Do you see any intake above 100mg (7 other studies included in the meta)  to be safe?

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