Soy Good or Not Soy Good?

Even dietitians occasionally question their recommendations due to myths or fears circulating in the public. People read all sorts of propaganda online, and some of it is so convincing it can be hard to decipher fact from fiction.

Recently, I’ve heard a lot about soy foods. When I asked people about the source of their beliefs, their response was often “I don’t know, but I know I heard it somewhere” or “I’m not sure, but I heard it wasn’t good so I just avoid it.” So, I went searching for a more concrete answer.

I first turned to Google to see what was being said, and I found some pretty scary stuff out there. The problem is, none of what I found was backed up by solid research. One person went so far as to call soy, and all beans for that matter, “evil food.” I then turned to more research driven search engines such as PubMed, Google Scholar, and Web of Science. All I could find there were studies reporting soy’s positive influence on health. No wonder there is so much confusion!

So, what’s with all of the contradiction? A lot of what it has to do with is the amount and type of research out there. But hopefully by the end of this article things will be a bit more clear.

The back story…

To start, soy is a plant native to Asia that has been around for at least 5,000 years (that’s a looooong time). It has been a part of Chinese culture since the 2^nd century, and came to the US in the 1700’s. It is an economically important crop, is easy to grow, and provides an excellent source of protein for both humans and animals. In 1999, soy crops made up 27% of the total crop area in the United States¹.

Whole soy (like edamame) is chiefly made up of proteins, isoflavones, lecithin, fiber, and phosophlipids (see diagram below)². Soy is an excellent form of vegetable protein, but is not a complete protein because it lacks the essential amino acid methionine¹.  Isoflavones are compounds chemically similar to estrogen in the body – also called phytoestrogens (no boys, it will not give you man-boobs). The two main types of isoflavones are genestein and daidzen. Lecithin is a preservative found naturally in a number of different foods as well as soy foods. Fiber is found mainly in fruits, vegetables and whole grains, and to learn more read my previous blog entry.

 

Soy components not in equal proportions as indicated. Image only for demonstration.

 Cardiovascular Disease

According to the Mayo Clinic², numerous human studies report that adding soy protein to the diet can moderately reduce blood cholesterol levels and low-density lipoprotein (LDL) levels - the "bad" cholesterol. Furthermore, according to the majority of these studies, soy’s heart healthy effects can be linked to phytoestrogens found naturally in the plant.

Cancer

The estrogen found in our bodies is linked to the progression of hormonally-sensitive cancers (like breast and prostate cancer)³. In these types of cancers tumors grow when estrogen locks to estrogen receptor cells, causing a series of signals that instruct tumors to grow. However, phytoestrogens are weak imitations of estrogen, and when it comes to tumor growth some studies indicate phytoestrogens can help slow tumor growth. They do this by locking with estrogen receptors and blocking estrogen from ever attaching to receptor sites³. However, other studies like that of Dr. Bill Helferich, found that injecting genestein into mice made breast tumors grow.⁴ It is important to note is that these studies are not as influential on dietary recommendations because they occur in rodents and in isolated periods of time. So, as of now, natural soy (tofu, edamame, milk, temphe, miso ect.) is thought to have a protective effect against breast and prostate cancer.

If you take a look at studies of Asian populations, where soy is a regular part of the diet, researchers have found that cancer risk is about 24% lower in people who ate more soy when compared to those who ate less.³  Some studies suggest that the protective effects of soy for breast cancer in Asian cultures is due to the fact that consumption of soy begins at an early age, when breast tissue is still developing ³. The jury is still out on that fact, but it will be interesting to see if adding soy into the diet early on has any benefit.

Additionally, when it comes to cancer, natural soy has antioxidant properties, which help reduce the formation of cancer-causing free radicals.^{3, 5}

Menopause

Because of soy’s high concentration of phytoestrogens it was, at one time, believed that soy supplements were effective. However, an article published in the New York Times states that American Menopause Foundations and the North American Menopause Society suggest that moderate soy supplementation is ineffective in the treatment of menopause.⁴

Pediatrics

Many parents are naturally concerned about everything they feed their child, and that’s a good thing. Most children go through a “picky” phase making meal-time and nutrient intake challenging. So making sure your child gets enough nutrition can be nerve racking! Furthermore, with the prevalence of food allergies parents are more aware than ever of potential allergens in our food supply.

Natural soy is an excellent source of protein and can be a good alternative when allergies persist. However, if your child is allergic to peanuts there is some evidence to suggest that they may also be allergic to soy milk as well.¹ So why not just supplement right away with almond or rice milk? A great idea, but the problem is bioavailability, rather, how much your child actually ends up absorbing. ¹

When it comes to available nutrition, nothing is better than cow’s milk- see diagram below. But if your child has an allergy, or you prefer non-animal sources, I would first choose fortified soy milk, then almond milk, then rice milk. But always choose a fortified alternative to make sure they’re getting enough calcium to help bone development.

Milk/"Milk" Comparison chart (per 1 cup)*
	Calories	Fat/Saturated	Protein	Carbo- hydrate	Fiber	Calcium	Vitamin D
Cow’s	80-150 (nonfat to whole)	0.5-8 g fat/ 0-5 g saturated	8-9 g	12-13 g	0 g	30% DV	25% DV
Goat's	90-150 (nonfat to whole)	2.5-8 g fat/ 1.5-5 g saturated	7-8 g	9-12 g	0 g	30% DV	Up to 30% DV
Soy	60-130	2-6 g fat/ 0-0.5 g saturated	4-12 g	5-15 g	0-4 g	4-30% DV	Up to 30% DV
Rice	110-120	2.5 g fat/ 0 g saturated	1 g	20-24 g	0 g	2-25% DV	Up to 25% DV
Almond	60-80	2.5-4.5 g fat/ 0-0.5 g saturated	2-9 g	5-11 g	0-4 g	20-30% DV	Up to 25% DV
Hemp	110-130	3-7 g fat/ 1 g saturated	4-5 g	6-20 g	1 g	2-46% DV	Up to 25% DV
*Data reflects a sample of 20 readily available milks/“milks.” For plant-based “milks,” we included only plain varieties—both sweetened and unsweetened, when available.  Source: eatingwell.com6

(Tip: shake the container before pouring any calcium fortified juice or milk. Calcium is a heavy element and will often sink to the bottom of the container reducing the amount of calcium you get per serving!)

Challenges in research

Every piece of literature I uncovered touting the benefits of soy stressed the importance of further research to determine weather or not soy can be recommended as a way to help prevent cancer. At this time the belief is that natural soy (tofu, edamame, milk, temphe, miso ect.) may help protect against cancer when eaten in moderation.⁵

As referenced earlier in the article, several rodent studies have suggested that soy might encourage tumor growth. The difficulty with animal studies is that this type of research occurs in a vacuum, where rodent subjects are fed (typically injected) with only one type of food for defined period of time. While this type of research is really important, we cannot make the direct link to humans because, well, rats aren’t humans, we don’t live in cages, and we eat a lot of different things.

According to the International Agency for Research on Cancer (IARC)⁷, several types of epidemiological studies (human studies) are considered when determining the cancer-causing effects of agents in our environment. While I won’t bore you with them all, the IARC suggests that intervention studies can provide strong evidence in determining something as cancer causing, much like the studies linking smoking cessation to lung cancer did. But this is not as easy when conducting dietary studies since our diets are so variable.

In the end…

It is my guess that all of the fear and confusion comes from the varied results among research. It’s natural to want to “air on the side of caution” when it comes to preventing cancer, especially since their appears to be some things we still don’t know.

However, when in doubt, I’m going to remind myself that soy has been around for over 5,000 years! And, as of now, research suggests that soy may help prevent heart disease and cancer.

Bottom line: Consume natural forms of soy knowing that you’re doing something good for yourself. If you want to prevent cancer DO NOT use any form of tobacco ever (that includes cigarettes, cigars, and chewing tobacco), eat a variety of fruits and vegetables, limit meat, exercise, and visit your doctor regularly.

1.     Friedman, Mendel; Brandon, David L. (2001). Nutritional and Health Benefits of Soy Proteins. Journal of Agricultural and Food Chemistry, 49, (3), 1069-1086.

2.     Natural Standard: The Authority on Integrative Medicine. (2012). Soy (Glycine max). Retrieved from http://www.mayoclinic.com/health/soy/NS_patient-soy

3.     McCullough, Marji ScD, RD. (2012). The Bottom Line on Soy and Breast Cancer Risk. Retrieved from http://www.cancer.org/cancer/news/expertvoices/post/2012/08/02/the-bottom-line-on-soy-and-breast-cancer-risk.aspx

4.     Tarkan, Laurie. (2004, August 24). As a Substitute for Hormones, Soy is Ever More Popular, but Is It Safe?. The New York Times. Retrieved from http://www.nytimes.com/2004/08/24/health/as-a-substitute-for-hormones-soy-is-ever-more-popular-but-is-it-safe.html?pagewanted=all&src=pm

5.     Miller, Paige F. PhD, MPH, RD; Snyder, Denise C. MS, RD, CSO, LDN. (2012). Phytochemicals and Cancer Risk: A Review of the Epidemiological Evidence. Nutrition in Clinical Practice,  27 (5), 599-612.

6.     Meredith Corporation. (2013) A Buyers Guide to Milk Alternatives. Retrieved from   http://www.eatingwell.com/healthy_cooking/healthy_cooking_101/shopping_cooking_guides/a_buyer_s_guide_to_milk_part_ii

7.     The World Health Organization International Agency on Research for Cancer. (2006). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Preamble. Pg. 8, Lyon, France.