Soy and Childlessness

Summary A cross-sectional study from AHS-2 has found an association between eating more soy and an increased rate of not becoming pregnant or having a child. The study was cross-sectional and had some limitations. It should not be considered proof that soy causes childlessness.

A report from Adventist Health Study-2 was recently released examining the association between soy intake (measured as isoflavones) and childlessness (1).

The authors write:

“The results suggest that when the isoflavone intake exceeds approximately 40 mg per day, the overall lifetime risk of never becoming pregnant increased by 13% and that of ever giving birth to a live child was reduced by approximately 3%. The associations were consistently found to be stronger in women who reported having had difficulties in becoming pregnant (1 straight year or more without success to become pregnant).”

40 mg of isoflavones per day is the equivalent of about 2 servings of soy per day.

There are some reasons not to conclude that soy causes childlessness:

• The author’s stated that, “One major limitation in our study is that we are not able to distinguish with certainty between involuntary and voluntary childlessness.”

• The finding for never becoming pregnant was 1.13 (1.02, 1.26) for women eating 40 mg of isoflavones per day compared to those eating only 10 mg. This is barely statistically significant.

• It was a cross-sectional study with relatively weak findings. Cross-sectional studies can indicate what should be studied prospectively and in clinical trials, but cannot prove causation.

• The researchers did a lot of testing with many different models, the results of which didn’t always agree. The authors stated in their discussion, “[G]iven the somewhat exploratory nature of our analyses and the many statistical tests conducted, we do not believe that [an inconsistency they found] deserves much emphasis at this point.” Indeed – that could apply to their main finding.

Despite the limitations, if someone is having a hard time becoming pregnant, cutting out the soy might be something to try.

The study is linked to in the reference below and is free to the public.

I have updated the article, Soy: What’s the Harm?


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1. Jacobsen BK, Jaceldo-Siegl K, Knutsen SF, Fan J, Oda K, Fraser GE. Soy isoflavone intake and the likelihood of ever becoming a mother: the Adventist Health Study-2. Int J Womens Health. 2014 Apr 5;6:377-84. doi: 10.2147/IJWH.S57137. eCollection 2014. | link

21 Responses to “Soy and Childlessness”

  1. Corrin Radd Says:

    Obviously anecdotal, but for what it’s worth my wife eats lots of soy–tofu, soy milk, tempeh, soy “meats,” dogs and sausages and we had not trouble having kids. We planned for two kids and had two; the only times we tried to have kids, we had kids. We wanted to have our kids in May and we had them in May. Two years apart. And we were both over 35 when we had them, so not even in the prime of our fertility.

  2. Jack Norris RD Says:

    Hi Corrin,

    Yes, it couldn’t possibly be the case that all women who eat two servings of soy per day cannot get pregnant. Even if this association were causal, it still wouldn’t mean that most women eating 2 servings of soy per day would have a hard time getting pregnant. That’s one of the problems with the way nutrition research is presented — it’s never an all or nothing thing but rather, in most cases, some small percentage of difference. In this study, only 15% of the women in the top soy intake categories had a difficult time getting pregnant. With a 13% higher risk than those in the lowest category, that would mean the higher soy category would have had 13% of women with problems getting pregnant rather than 15% with problems, assuming soy caused this increase.

  3. Bob M Says:

    “One major limitation in our study is that we are not able to distinguish with certainty between involuntary and voluntary childlessness.”

    Don’t worry, I’m sure the mainstream press will note this! /s

  4. Steve E Says:

    Did they account for the gap between reduction in pregnancies and reduction in live births? That makes me think this is more of a social occurrence (ie, women who eat more soy have fewer unplanned pregnancies, so a greater percentage of their pregnancies are carried to term) than a biological occurrence. …or maybe soy prevents miscarriage. Sounds like more research is needed.

  5. VWG Says:

    Thanks for all of your work, Jack. One huge question about isoflavones and phytoestrogens… Soy gets a bad rap for these containing these chemicals, for better or for worse. But I’ve read that a huge range of plant-based foods contain these chemicals. I’ve heard flaxseed contains even more phytoestrogens than soy. And other beans, from garbanzo to kidney to pinto, to peas contain them. Nuts do too, including almonds, peanuts, walnuts, and pistachios. Even fruit and veggies contains phytoestrogens like berries and broccoli.

    It seems that even if you cut out soy from your diet, primarily to not take in so many phytoestrogens and isoflavones, it might not make much of a difference considering so many other healthy vegan staples have the same compounds. What are your thoughts on this? Why is soy singled out? As a vegan, this is something I wonder about. I know these chemicals have a lot of benefits, but also some drawbacks, especially when too much is consumed.

  6. Jack Norris RD Says:


    Thank you for your kind words!

    As you seem to know, the phytoestrogens in soy, isoflavones, are not the same as lignans, the other phytoestrogens found in many plant foods but especially flaxseeds. To my knowledge, lignans have not been studied nearly as exhaustively as isoflavones and I don’t know if they have much affect on estrogen-related functions in the body.

  7. Dan Says:

    Hi Jack,
    Significantly off-topic, but I remember reading some time ago a pundit saying that meat contains all essential vitamins and minerals with the exception of vitamin C (which matters less on a low carb diet). I was wondering if this is true and I was also wondering what vitamins, minerals, etc. legumes contain when they replace meat as the traditional source of complete protein in a vegan diet.

    My thinking is that legumes are a significant source of complete protein, calcium, iron (non-heme), carbs and fiber (the latter two not found at all in meat). Is there anything else that legumes contain that significantly or substantially replicates what’s found in meat or exceeds it?

  8. Jack Norris RD Says:


    > with the exception of vitamin C (which matters less on a low carb diet).

    Why is that?

    Legumes are good sources of folate while meat is not. Can’t think of anything else of much significance off the top of my head.

  9. Dan Says:


    >Why is that?

    I’m afraid I can’t remember.

    By the way, is there any evidence that glutamine supplementation in weight-lifting helps to relieve or reduce muscle soreness the day after a work-out? A personal trainer told me this, but I’ve never heard it before. Thanks.

  10. Jack Norris RD Says:

    Hi Dan,

    Someone told me about this site,, that seems to be an excellent source of information. Here is their page on glutamine:

    What they say there is also my understanding, though I’ve never done a lit review.

  11. Dan Says:

    Hi Jack,
    Thank you for the reference. I am reading it. The reason I ask is that after starting a weight-training routine with a physical trainer, I find that my left arm is killing me today, especially on full extension at the elbow (I am obviously right arm dominant). He suggested glutamine to prevent this, knowing that I am vegan (he also takes it himself).

    I do try to eat a lot of protein in the form of legumes (as well as some grain and nuts and seeds), and it’s possible that any (even omnivorous) wimp who is pretty de-conditioned (although I have good cardio) would face the same muscle soreness the day after starting a weight-training routine, and I am not just glutamine-deficient. I hesitate to take protein powder supplements or isolated amino acids, but if this issue persists, I may have to. Do you have any further thoughts?

  12. Jack Norris RD Says:

    Hi Dan,

    That sounds more like an injury than just typical muscle soreness. I don’t think glutamine is going to help. You should probably ice it, though.

  13. Dan Says:


    >That sounds more like an injury than just typical muscle soreness. I don’t think glutamine is going to help. You should probably ice it, though.

    Yes I think you’re right that it was an injury. It seems to finally have started to improve (after 4 days). However, I think some injuries could be worsened by nutritional deficiencies as the musculature of a human being is a highly metabolic organ, and multiple cofactors and coenzymes are required for optimal functioning, regeneration of microtubules, and healing. I therefore wonder if my vegan diet is missing some essential micronutrient, one of the “soft” or “gray zone” ones that are not generally recommended to vegans (i.e. not B12, but something like an amino acid of a lower-series B vitamin). Guess it’s time to hit peacounter.

  14. Jack Norris RD Says:


    If it was an injury, which is not uncommon in weightlifting among meat-eaters and vegetarians alike, then it would take some time to heal no matter what sort of diet you have. The only nutrient that I think your diet is likely to be low in that might help healing is zinc.

  15. Jack Norris RD Says:

    > The only nutrient that I think your diet is likely to be low in

    I didn’t phrase that right – it sounds like I think there is greater than a 50% chance that your diet is low in zinc. Rather, I think there is *some* chance that it could be. Of course, if you’re not eating enough protein as a function of not eating enough calories, that could be a problem for wound healing, too.

  16. Dan Says:

    Jack, thanks for all the advice!

    According to peacounter, I am adequate on zinc but inadequate on calories. I am getting 1759 kcal/d and according to my body physiology and activity levels, I should be getting 2400 kcal/d. Here is a question I have. Since I am starting weight training, I am concerned to get enough protein in my diet and am wondering if you would recommend protein powder supplementation for someone in my situation. According to peacounter, I am getting 70 g of protein per day, which is clearly over 1.1 g/kg (I weigh 124 lbs). I have some qualms about protein supplements including the fact that many include things like L-carnitine, choline, high dose magnesium, which may all be detrimental when given as a supplement, and I’ve also noticed that most protein powders are whey or casein based. My trainer tells me that it is more difficult to extract protein from plant foods than from dairy or meat, so should I just further up my intake of legumes? It wouldn’t be too hard for me to put some peas or more beans in my morning smoothie. Thanks for all your advice (incidentally, the arm is much better today despite my workout, so I am not sure if it was a true injury or not – it lasted a good 3.5 days and was so sore I couldn’t extend my forearm at the elbow without pain – i.e. possibly biceps tendinitis).

  17. Jack Norris RD Says:


    I’m glad your arm is feeling better.

    I sometimes worry that the formulas the Institute of Medicine uses (and that PeaCounter uses) for determining energy needs overestimate. Have you tried another site to see how it compares?

    > My trainer tells me that it is more difficult to extract protein from plant foods than from dairy or meat,

    It’s a bit more difficult; the one study I know of that measured it found that the protein was 2.6% less digestible.
    If you’re eating plenty of legumes, you probably don’t need protein powder. You could also add some silken tofu which should work well in a smoothie and provide extra protein.

  18. Dan Says:

    I haven’t tried another website for determining my energy requirements but both peacounter and data from the gym I use concur pretty closely (2350-2400 calories per day).

    Great idea about the silken tofu. I hadn’t thought of that. I will pick some up and start using it in my breakfast smoothie. That should give me some extra calcium too.

  19. Ariann Says:

    My experience with calorie counting is that the only way to know how many calories you require is to track how many you’re eating, track your weight, and compare the two. If you lose weight (and don’t want to), you need more calories. If you gain weight (and don’t want to), you need fewer calories, etc. Calculators are only very general guesses.

    I’ve been weight-lifting pretty seriously for several months and making significant gains in strength (and I’m a woman, so theoretically that’s harder anyway), while losing weight slowly, eating around 70g protein a day. No protein powder, no need to go crazy. The way you react to weight training also has as much to do with genetics as anything else.

  20. Dan Says:

    Just a follow-up. I found that extra firm, low-fat tofu has 16 g of protein per 88 g serving, whereas soft tofu has only 5 g of protein per 88 g serving (based on amounts in my grocery store brand). I therefore bought the former.

    I think your points are excellent. Indeed, not only weight change as an informative variable, but I would also track energy level and hunger cravings. Since I started working out, I have lost 1.5 lbs and I was already very thin to begin with. This tells me that I am in a net energy deficit. I also don’t eat a large amount of carbohydrate because I have a previous history of metabolic syndrome. If I start bonking during work-outs, I will definitely have to increase my calories (I also do pretty vigorous cardio).

  21. Enola Knežević Says:

    So, they didn’t distinguish between involuntary childlessness and voluntary childlessness (childfreedom). I can think of at least 2* reasons why somebody following a vegan diet (that would cause a higher soy intake) would also be childfree (never ever want to reproduce):

    1. not having children is the action that lowers one’s carbon footprint the most, while vegan diet is likely the second best action
    2. wanting to reduce suffering, to those who already exist by being vegan, as well as to potential sentient beings by never bringing them to this world (philanthropic antinatalism)

    In any case, do not by any chance rely on soy! Take contraception! I know vegetarians and vegans who had been affected by unplanned pregnancies.

    * a study found a positive correlation between IQ and vegetarianism, and people with higher IQs have fewer children, later in life, and are also more likely to be childfree.

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