I'm attempting to go a couple of weeks on a vegan diet inspired by "The Game Changers". However, everywhere I look I see most vegan recipes including soy: soy mince, soybeans, tofu, tempeh, or soy milk. Every recipe titled "high-protein vegan recipe" contains soy.

I've read multiple articles, including on this site, that state that soy protein is not good for muscle growth: estrogen by-product with high-consumption of soy counteracts testosterone benefits. A quick search shows answers that say "avoid soy altogether". Other websites say that you should limit soy protein intake to 3 - 4 servings to avoid these negative side effects and follow up saying that this shouldn't be a huge hurdle as you can easily consume your daily protein requirements (50 g) in under 3 - 4 servings.

My problem here is that I am currently consuming 180 g of protein per day in the form of whey isolate, ground beef, chicken, fish, and legumes. This has been a good number for me and I've seen a consistent strength increase. I can't see myself getting 180 g of protein without overstepping these 3 - 4 servings of soy. Three cups of soy milk is only 24 g of protein, 1.5 cups of tofu is 30 g of protein.

My questions:

  • Is soy protein really detrimental to strength and muscle growth in high consumption?
  • Is there a version of soy that does not have negative side effects on strength and muscle growth?
  • What does an increase of estrogen even look like at the gym? (i.e. is this just a marketing ploy? There's plenty of strong women out there.)

I realize this is mainly a nutrition question but I figured I would give it a shot as it relates directly to my fitness requirements. Consuming 2 kg of beans in a day seems like it just can't be sustainable.

Background and Related Fitness Information:

I began powerlifting about a year and a half ago but have only really started watching my diet within the last six months. I calculated a requirement of 180 g of protein per day from the 0.8 g to 1.2 g of protein per pound of bodyweight. I currently weigh 195 lb at a height of 6'0. Male. Canada.

My goal is to improve in the main lifts of powerlifting as well as the overhead press. The goal numbers are arbitrary and based on 250% to 100% body weight. Muscle growth is also important. I'm not focused on bodybuilding but looking good is nice.

 1. Squat       --> Current: 355 lb.   Goal: 405 lb.
 2. Bench Press --> Current: 225 lb.   Goal: 315 lb. 
 3. Deadlift    --> Current: 420 lb.   Goal: 495 lb.
 4. OHP         --> Current: 135 lb.   Goal: 225 lb.

Since starting to track my nutrition and increase protein intake I've noticed that my recovery time is much faster and it has helped push through a plateau. I'm currently following a new 12-week peaking program with a 6-8% 1RM increase in Week 12. This week's workout (week 3) looks like the following:

Monday:     High Bar Squat (4x5 @ 250 lb), Walking Lunges (3x8), Single Leg Calf Raise (3x8)
Tuesday:    Strict OHP (4x8 @ 95 lb), Flat Dumbbell Press, One Arm Row, Face Pulls
Wednesday:  Rest*
Thursday:   Snatch Grip Deadlift (4x8 @ 270 lb), Leg Curls, Back Extensions
Friday:     Bench Press (4x8 @ 160 lb), Pull-ups, Seated Shoulder Press, Lat Pull Down, Dumbbell Rotations
Saturday:   Rest*
Sunday:     Rest**

*or arms: bicep curls, tricep extensions, preacher curls, dips, farmer walks
**or cardio: 30 minutes rowing.

Unfortunately, either my Google-fu is lacking or the internet believes "powerlifting", "vegan", and "high-protein" are oxymorons. I don't believe I can achieve my fitness goals without achieving nutrition goals as they go hand-in-hand.

  • 2
    Hi C. This is a very good question, and it deserves answers. But as you may know, questions are off-topics on this site if they relate to food, but without being directly related to exercise. I don't want to close this question, as it's so carefully thought-out and articulated, so if you could elaborate on what kind of exercise you do that makes you seek out 180g of protein per day, that would eliminate any doubt.
    – Alec
    Commented Oct 8, 2019 at 18:38
  • In that same vein, @JohnP, do you remember that study you and I discussed a while ago, which concluded that the whole "1g of protein per pound of body weight" is a huge overestimation? I think it may become relevant for this question, but I can't remember where we discussed it.
    – Alec
    Commented Oct 8, 2019 at 18:40
  • @Alec - I think so? Might need to pull up a few old posts.
    – JohnP
    Commented Oct 8, 2019 at 20:08
  • Also, @C. Lange I agree. This is a well thought out question and deserves an answer. Could you outline your exercise program a bit and why you think you need the level of protein you do? I realize that's a bit of a dodge, but I'd rather do that than have the door opened to flat out nutrition questions.
    – JohnP
    Commented Oct 8, 2019 at 20:10
  • @Alec - One of these? fitness.stackexchange.com/questions/15310/… fitness.stackexchange.com/questions/792/… fitness.stackexchange.com/questions/6362/… - Or possibly one of the frozen/deleted discussion rooms...
    – JohnP
    Commented Oct 8, 2019 at 20:23

1 Answer 1


This is not really going to be a definitive answer, as you can find studies that support almost any position, so what I'm looking at for this is the trend of the studies that I've reviewed.

Overall, I am finding that there are more studies that show soy protein does not have a detrimental effect on free testosterone, especially when connected to a weightlifting/workout regimen or controlled for daily intake. One of the studies that I reviewed was a meta study, which is basically a review/collection of other studies. This one reviewed ~ 45 studies of various structures and came to the conclusion that soy proteins had no effect on reproductive hormones.

That is corroborated by this study which compared soy forms and whey protein in men combined with a resistance program (20g supplemented daily), and concluded there was no difference, as corroborated with another study that showed no effect on testosterone, but was limited to "two servings" per day. One of those serving choices was 29g of of soy protein powder.

On the flip side, a study of "healthy males 18+" showed decreased testosterone levels, however there was no mention of resistance training and the intake level was 56g. Another one that makes no mention of resistance regimen (And also fails to note the amount of soy, only isoflavones) also showed a decrease in serum testosterone.

One of the most interesting studies I read (which I admit to not understanding all of it, it's very heavy in the messaging and structure), showed that while there wasn't a detrimental effect to soy, there were greater results on growth from the whey protein. However, the really interesting part was that soy supplementation showed a greater effect on Type I fibers (slow twitch), while whey protein supplementation had a greater effect on Type II (fast twitch) fibers. They note that this warrants further study, as it is a new finding.

So overall, my conclusion (And I reviewed more studies, Google scholar is a great place to start) is that soy protein is not going to have a detrimental effect in lower doses and combined with resistance training. If you are still really worried about it, there are also non soy protein powders available, such as pea protein powders. There is some evidence that larger doses of soy protein in the absence of a resistance program can lower testosterone. There were no studies that were as short of a period as two weeks, however. Most were 12+ weeks, so I would think that for a two week period and combined with resistance training there should be no negative effect for you.

  • Thank you for the research! I will definitely have to read through these findings later -- they're fairly dense. "detrimental effect in lower doses": did any studies point out what this dose limit was?
    – C. Lange
    Commented Oct 9, 2019 at 19:40
  • @C.Lange - No, but I suspect that it is upwards of 40+ grams, and it may be that the isoflavone content also plays a large role.This was not complete in depth research, but more of a meta analysis. The commonality that I found was that in high (50+ grams) doses combined with no apparent resistance program was when the greatest negative effects were observed. as well as the greater isoflavones.
    – JohnP
    Commented Oct 9, 2019 at 20:25
  • 1
    Do all of the studies you looked over use soy protein powder as opposed to other soy products? I remember reading a while back that there was a fair difference between fermented soy and regular soy, the former being better for digestion, as well as other reasons I can't quite remember.
    – Dark Hippo
    Commented Oct 10, 2019 at 8:08
  • @DarkHippo - No, the "another study" that links to nature.com had different soy choices other than the protein powder, and there was one other that had 3 different types of soy protein in use. I don't recall seeing fermented soy, however.
    – JohnP
    Commented Oct 10, 2019 at 15:49
  • Great, thanks. I'll give that one a look over
    – Dark Hippo
    Commented Oct 11, 2019 at 6:58

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