American Cancer Society on Soy & Breast Cancer

If you’ve read my articles on soy (Response to Not Soy Fast, Soy: What’s the Harm), there’s nothing new here, but it’s good to hear it from an organization like the American Cancer Society (ACS):

The Bottom Line on Soy and Breast Cancer Risk
August 02, 2012
By Marji McCullough, ScD, RD


“Bottom line: Even though animal studies have shown mixed effects on breast cancer with soy supplements, studies in humans have not shown harm from eating soy foods. Moderate consumption of soy foods appears safe for both breast cancer survivors and the general population, and may even lower breast cancer risk. Avoid soy supplements until more research is done. So, enjoy your occasional tofu stir-fry or tofu burger – they are unlikely to increase your risk of breast cancer and, on balance, are some of the healthier foods you can eat!”

Warning: There are the typical Weston Price Foundation-type comments after the article – the myths about Asians eating only fermented soy and fermented soy being significantly different than other soy. Too bad they allow comments which will possibly just serve to scare people. And I realize that I’m saying that as someone who allows comments on my own blog, but it’s one thing to be an RD blogger and another to be the strategic director of nutritional epidemiology for the ACS. Of course, that doesn’t mean Dr. McCullough is infallible, but if someone whose opinion is worthwhile has an objection to her article, they can contact the ACS behind the scenes and she can correct the article if they have a valid point. Just my two cents!

(Thanks, Matt.)

17 Responses to “American Cancer Society on Soy & Breast Cancer”

  1. Ivy Says:

    What do they mean by occasional? As in enjoy your occasional tofu stir-fry.

  2. Jack Norris RD Says:


    Good question. Maybe she’s trying not to give an exact amount since no one really knows what the ideal amount of soy might be. I think there is solid evidence that up to 3 servings a day is safe (unless you have subclinical hypothyroidism). I’ll write her and ask if she can be more specific.

  3. Bertrand Russell Says:

    Important to note, though, that this doesn’t mean that eating soy (or eating vegan) means you *won’t* get breast cancer (or heart disease, or lung cancer, etc.).

  4. Ivy Says:

    Thanks, Jack. I’d appreciate that.

  5. Jack Norris RD Says:


    I heard from Dr. McCullough and she said:

    “Thanks for contacting me, that’s a good question. You are correct that no one knows what the ideal amount of soy would be. Another epidemiological study that came out last year also supports that breast cancer survivors (in China or the US) consuming >10 mg soy isoflavones/day had lower risk of breast cancer recurrence (Nechuta AJCN 2012). The amount of isoflavones in soy products varies, as you know, another reason why it’s not straightforward to come up with an ideal number of servings per day. And the range of intakes in US women is lower than in Asian women. But I’d agree that given the evidence, consuming 2-3 servings of soy foods per day appears to be safe.”

  6. Dan Hackam Says:

    Jack, I have a question for you (as a personal consumer of a vegan diet). This question seems to come up a lot. How can a vegan diet be considered “healthy” if it requires so many supplements to stay balanced? Personally, I take DHA, vitamin B12, vitamin D, and iodine, since, based on the reading I have done, these nutrients are not adequately supplied in a vegan diet. Sometimes I feel more like a patient than a person, popping all these pills. Others might have to add iron and calcium to stay healthy (as well as vitamin C to absorb that iron). Beyond the ethical issues – which I consider enormous – would occasional meat or egg consumption be healthier?

  7. Jack Norris RD Says:


    Note that vegans can get enough iodine by eating seaweed and they can get enough vitamin D from the sun and/or UV-exposed mushrooms.

    That aside, here is my answer, mostly regarding vitamin B12, but it touches on other nutrients:

    > would occasional meat or egg consumption be healthier?

    I would assume that fish contains iodine if it comes from the ocean (or even some lakes), but I don’t know that for sure. If it does, then you could get DHA, B12, and iodine from an occasional serving of fish (2-3 servings per week). If you eat more fish than that, you are risking too much mercury. That much fish will not provide enough B12, so you would need some other animal product as well – maybe a glass of milk per day. Dairy also contains iodine, but from contamination and sometimes vitamin D from fortification.

    The only substantial, natural animal food source of vitamin D is cod liver oil, but eating cod liver oil seems the same as taking a supplement to me.

    To sum it up, if it is important to someone not to have to take supplements, and they get enough sun to make most of their vitamin D, then a plant-based diet with a glass of milk per day and serving of DHA-containing fish twice a week is probably the healthiest way to go about it based on the epidemiological studies of vegans, lacto-ovo vegetarians, pesco-vegetarians, and meat-eaters.

    Iron absorption adds another variable to this which could be handled in different ways.

  8. Ivy Says:

    The only nutrient vegans have to supplement is B12, and you might be able to meet most of that need via fortified nondairy milks. Everyone I know takes a form of DHA. Not too many people like fish oil. Some take flaxseed oil, though I don’t know if that helps. It’s all so confusing! I think you have to be careful to take in the proper nutrients with any diet. It’s easy to lead a junk food life and not get the proper nutrients.

  9. Dan Says:

    Jack, thanks for the detailed response.

    I contend that milk and fish are technically not part of a true vegan diet and while I understand your point about supplements potentially replacing these food sources, I would still contend that a plant-based diet is lacking in vitamin B12 and DHA. I think you agree with this, at least in principle, since you recommend both of these as supplements to true vegans. As for iodine – I agree it could come from seaweed as an add-on to a terrestrial plant-based diet, and vitamin D obviously from sunlight (though difficult to get that all year round in northern climes – for either omnivores or vegetarians).

    My bottom line: if a plant-based diet is low in critical micronutrients like vitamin B12 and DHA, and requires very careful balancing of proteins from multiple sources to get all of the essential amino acids that are so readily available in meat, it has to be asked whether a vegan diet is truly optimal for health. I eat it in large part for ethical reasons, not health ones. At the same time, I like the cholesterol-lowering effects of vegetarianism which can be dramatic in many individuals (they were certainly for me). Lastly, as an aside, you also have to be very careful not to over-eat carbohydrates on a plant-based diet, which is very easy to do, slipping one into metabolic syndrome. This is why I am a low-carb vegan – a very tough tightrope to walk!

  10. Jack Norris RD Says:


    I don’t mean to be contentious, but since you are “contending” so many things :), here are my responses.

    > I contend that milk and fish are technically not part of a true vegan diet

    Is someone disagreeing with you about that?

    > I would still contend that a plant-based diet is lacking in vitamin B12 and DHA

    It’s not clear to me that humans need DHA, even though I recommend supplementing with it to be safe. It is certainly not a “critical” micronutrient, as many vegan kids have grown up without it.

    > requires very careful balancing of proteins from multiple sources

    A vegan diet does not require this. You just need a couple serving of legumes each day, which come in a wide variety of forms.

    > you also have to be very careful not to over-eat carbohydrates on a plant-based diet,

    Not any moreso than on most other diets that humans are eating. In other words, if you eat a lot of refined carbohydrates, and particularly if you eat too many calories, then this could be an issue. But this is true of all diets. The carbohydrates in most whole plant foods should not contribute to metabolic syndrome for most people.

    > it has to be asked whether a vegan diet is truly optimal for health.

    I think it can be optimal, but not necessary. In other words, based on the knowledge we have today, you can plan other diets to be just as optimal.

  11. Dan Says:

    I agree with you about DHA. In fact, a recent very large analysis from the EPIC-Norfolk study showed that despite very large differences in DHA dietary intake between fish eaters, meat eaters, vegetarians and vegans, blood levels of DHA did not differ by all that much. The authors suggested that increased conversion of upstream precursors such as ALA to DHA may be responsible, and their statistical analysis suggests this (as precursor ratios were increased).

    See: Dietary intake and status of n-3 polyunsaturated fatty acids in a population of fish-eating and non-fish-eating meat-eaters, vegetarians, and vegans and the product-precursor ratio [corrected] of ╬▒-linolenic acid to long-chain n-3 polyunsaturated fatty acids: results from the EPIC-Norfolk cohort.
    Welch AA, Shakya-Shrestha S, Lentjes MA, Wareham NJ, Khaw KT.
    Am J Clin Nutr. 2010 Nov;92(5):1040-51. doi: 10.3945/ajcn.2010.29457. Epub 2010 Sep 22. Erratum in: Am J Clin Nutr. 2011 Mar;93(3):676.

  12. Jack Norris RD Says:


    I didn’t find that study very persuasive and wrote this about it:

    “Vegans and vegetarians have been shown in many studies to have lower levels of long chain omega-3 fatty acids (EPA and DHA) than meat eaters. Table 4 shows the results of some of these studies. The general trend is that lacto-ovo vegetarians and vegans have lower levels of EPA and DHA in their blood. One exception is the 5 vegan women in the 2010 UK study who had, on average, higher DHA levels than even the fish-eaters. This is probably an anomaly for a few reasons. First, “vegan” was simply defined as someone who did not list eating animal products in their 7-day diet diaries. These vegans might have only been vegan for one week. Second, there were only 5 vegan women in the study making the finding unlikely to be statistically significant. Third, the standard deviation for the DHA levels of the vegan women was very high at 211 ┬Ámol/l. That means that one or two of the vegan women had very high levels of DHA but some have very low levels.”

    I don’t think there is any question that vegans have lower blood levels of DHA unless they are supplementing with DHA, or possibly taking very large amounts of ALA for a long time (we don’t have data on that, but it is plausible). The question is whether lower blood levels indicate lower levels in tissues (one would think it does) and if DHA is critical in tissues. I have read some interesting things lately which makes me wonder if DPA isn’t just as good as DHA.

  13. Dan Says:

    I am totally unsure whether any of these long-chain essential fatty acids are all that essential, and I’m not sure what the implications of a low DHA level are for long-term health. All of these epidemiological studies are biased by unmeasured confounders related to unappreciated lifestyle habits which are very important. A microalgal DHA supplement for true vegans is very expensive – a 200 mL bottle runs around $36 plus applicable taxes, with a single teaspoon-sized dose (5 mL) containing 200 mg of DHA. Thus far, five recent supplementation trials have all been negative, but the frequency of veganism in these studies would be expected to be very, very low (probably even less than the general population). Whether we need DHA or not is to my mind still very much an open question, even if the biotransformation rates from ALA are extremely low (though possibly much higher in vegans, judging from recent research in both animals and humans).

  14. John Says:

    Jack, can you say more about the soy-thyroid connection? Anything we need to watch out for? (I have hypothyroidism, but it’s not subclinical–they have me taking levothyroxine and test my blood every six months to make sure it’s enough.)

  15. Jack Norris RD Says:


    Mark Messina told me that if you are on a thyroid drug, just keep your soy consistent and/or let your doctor know how much you are eating so that medication can be adjusted for it. That’s really about all I know.

  16. Miriam Says:

    Jack, first of all, thank you for your blog. I’m a Spanish pediatrician and a vegan, and I’m trying to learn as much as possible about vegan diets in babies and children in order to advise my vegetarian and vegan patients (not many in Spain…) I find your blog extremely useful and informative.
    Could you tell us what you know and think about the Weston Price Foundation?
    I have been readingabout their “soy alert campaign” and their general nutritional advice and I found their arguments very worrying.
    Thank you

  17. Jack Norris RD Says:


    You can probably Google the Weston Price Foundation and find out what their story is, but the main thing they seem to do these days is put out propaganda about soy. I respond to their usual talking points here:

    I wouldn’t put too much weight into anything they say, given how bad their track record is.

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