To maintain the low IGF-1 levels associated with a plant-based diet, one should probably eat no more than 3-5 servings of soy foods a day.
How Much Soy Is Too Much?
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So, we know 7 to 18 servings of soy a day may neutralize some of the beneficial effects of avoiding animal protein. At the same time, studies have repeatedly found that women who eat lots of soy appear to have a lower risk of getting breast cancer, and a better risk of surviving breast cancer than those who don’t eat soy. So is there some magic number of soy food servings we should shoot for?
So far we know that somewhere between 7 and 18 may not be so good, so more than 18 definitely gets the axe. This two year study found no effect on IGF levels of adding two servings of soy foods daily, whether they were tofu, soy milk, soy nuts, or the concentrated soy isolate found in plant-based meats, protein bars, or protein powder; still fine.
Still got a big range here. This study suggested 5 to 10 servings a day was bad— increased IGF—so we’re kind of slowly but surely narrowing down the safety window. Same year in Japan; three servings a day cleared the IGF radar. And then, that’s it. That’s all the science we have so far.
The bottom line is that legumes should be a part of everyone’s daily diet, which means lentils, peas, and/or beans, ideally with each of our meals—of which soy is an excellent choice. But, I recommend that we should probably stick to no more than 3 to 5 servings a day.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring watch the above video. This is just an approximation of the audio contributed by Kerry Skinner.
Please consider volunteering to help out on the site.
- Shu XO, Zheng Y, Cai H, Gu K, Chen Z, Zheng W, Lu W. Soy Food Intake and Breast Cancer Survival. JAMA. 2009 Dec 9;302(22):2437-43.
- Wu AH, Yu MC, Tseng CC, Pike MC. Epidemiology of soy exposures and breast cancer risk. Br J Cancer. 2008 Jan 15;98(1):9-14.
- Nagata C, Shimizu H, Takami R, Hayashi M, Takeda N, Yasuda K. Dietary soy and fats in relation to serum insulin-like growth factor-1 and insulin-like growth factor-binding protein-3 levels in premenopausal Japanese women. Nutr Cancer. 2003;45(2):185-9.
- Dewell A, Weidner G, Sumner MD, Barnard RJ, Marlin RO, Daubenmier JJ, Chi C, Carroll PR, Ornish D. Relationship of dietary protein and soy isoflavones to serum IGF-1 and IGF binding proteins in the Prostate Cancer Lifestyle Trial. Nutr Cancer. 2007;58(1):35-42.
- Arjmandi BH, Khalil DA, Smith BJ, Lucas EA, Juma S, Payton ME, Wild RA. Soy Protein Has a Greater Effect on Bone in Postmenopausal Women Not on Hormone Replacement Therapy, as Evidenced by Reducing Bone Resorption and Urinary Calcium Excretion. J Clin Endocrinol Metab. 2003 Mar;88(3):1048-54.
- Maskarinec G, Takata Y, Murphy SP, Franke AA, Kaaks R. Insulin-like growth factor-1 and binding protein-3 in a 2-year soya intervention among premenopausal women. Br J Nutr. 2005 Sep;94(3):362-7.
Images thanks to viviandnguyen via Flickr.
So, we know 7 to 18 servings of soy a day may neutralize some of the beneficial effects of avoiding animal protein. At the same time, studies have repeatedly found that women who eat lots of soy appear to have a lower risk of getting breast cancer, and a better risk of surviving breast cancer than those who don’t eat soy. So is there some magic number of soy food servings we should shoot for?
So far we know that somewhere between 7 and 18 may not be so good, so more than 18 definitely gets the axe. This two year study found no effect on IGF levels of adding two servings of soy foods daily, whether they were tofu, soy milk, soy nuts, or the concentrated soy isolate found in plant-based meats, protein bars, or protein powder; still fine.
Still got a big range here. This study suggested 5 to 10 servings a day was bad— increased IGF—so we’re kind of slowly but surely narrowing down the safety window. Same year in Japan; three servings a day cleared the IGF radar. And then, that’s it. That’s all the science we have so far.
The bottom line is that legumes should be a part of everyone’s daily diet, which means lentils, peas, and/or beans, ideally with each of our meals—of which soy is an excellent choice. But, I recommend that we should probably stick to no more than 3 to 5 servings a day.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring watch the above video. This is just an approximation of the audio contributed by Kerry Skinner.
Please consider volunteering to help out on the site.
- Shu XO, Zheng Y, Cai H, Gu K, Chen Z, Zheng W, Lu W. Soy Food Intake and Breast Cancer Survival. JAMA. 2009 Dec 9;302(22):2437-43.
- Wu AH, Yu MC, Tseng CC, Pike MC. Epidemiology of soy exposures and breast cancer risk. Br J Cancer. 2008 Jan 15;98(1):9-14.
- Nagata C, Shimizu H, Takami R, Hayashi M, Takeda N, Yasuda K. Dietary soy and fats in relation to serum insulin-like growth factor-1 and insulin-like growth factor-binding protein-3 levels in premenopausal Japanese women. Nutr Cancer. 2003;45(2):185-9.
- Dewell A, Weidner G, Sumner MD, Barnard RJ, Marlin RO, Daubenmier JJ, Chi C, Carroll PR, Ornish D. Relationship of dietary protein and soy isoflavones to serum IGF-1 and IGF binding proteins in the Prostate Cancer Lifestyle Trial. Nutr Cancer. 2007;58(1):35-42.
- Arjmandi BH, Khalil DA, Smith BJ, Lucas EA, Juma S, Payton ME, Wild RA. Soy Protein Has a Greater Effect on Bone in Postmenopausal Women Not on Hormone Replacement Therapy, as Evidenced by Reducing Bone Resorption and Urinary Calcium Excretion. J Clin Endocrinol Metab. 2003 Mar;88(3):1048-54.
- Maskarinec G, Takata Y, Murphy SP, Franke AA, Kaaks R. Insulin-like growth factor-1 and binding protein-3 in a 2-year soya intervention among premenopausal women. Br J Nutr. 2005 Sep;94(3):362-7.
Images thanks to viviandnguyen via Flickr.
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Title
How Much Soy Is Too Much?
LicenseCreative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)
Content URLDoctor's Note
This is the fourth in a string of videos on the role plant and animal proteins play in determining levels of the cancer-promoting growth hormone IGF-1. Also see IGF-1 as One-Stop Cancer Shop; Protein Intake and IGF-1 Production; Higher Quality May Mean Higher Risk; Animalistic Plant Proteins; and Too Much Soy May Neutralize Benefits. For the role soy plays in extending breast cancer survival, see Breast Cancer Survival and Soy. And, I’ve got dozens of other videos on soy.
For further context, be sure to check out my associated blog posts: How Much Soy Is Too Much? and Why Less Breast Cancer in Asia?
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