There’s a growing interest in plant-based sources of protein. No wonder – plant protein sources contain protein AND fiber, two of the most potent appetite suppressors. Looking for a way to get more non-animal protein in your diet? You have lots of options. Beans, lentils, whole grains, nuts, and even vegetables contain varying quantities of protein. The problem with all of these sources is they’re incomplete proteins, meaning they lack one or more of the essential amino acids your body needs to build new proteins. Yet there is one bean that IS a complete source of all the essential amino acids – soybeans.
Soy – A Complete Source of Plant Protein
Soy foods are popular among vegetarians and vegans. Being complete proteins gives them an advantage over other plant sources of protein. Soy is a staple in certain parts of the world, particularly Japan. In fact, historians note that tofu was mentioned in written records as far back as 950 AD. So, tofu is nothing new, but it’s a good source of B-vitamins and, depending on how it’s made, calcium. However, tofu isn’t the only soy-based food that offers plant-based protein.
Some soy sources of protein are fermented. Three examples are miso, tempeh, and natto. These foods, unlike non-fermented soy, contain gut-friendly probiotic bacteria. Some health experts believe fermented soy is healthier because it lacks two components found in unfermented soy: phytic acid and goitrogens. Plus, fermented forms of soy are easier to digest.
Phytic acid is in some plant foods and may reduce the absorption of minerals, including calcium, zinc, and iron. Goitrogens, present in fresh soy products, theoretically can reduce thyroid function. Fermentation greatly reduces the quantities of both of these undesirable components.
Although it’s healthier to stick to fermented forms of soy, goitrogens in soy are unlikely to be a problem as long as you don’t have an underactive thyroid. If you take medication for an underactive thyroid, it’s best to stick to fermented forms of soy. As far as concerns about mineral absorption, you’d have to eat a lot of unfermented soy to develop a mineral deficiency. Plus, soy is a good source of minerals, including calcium and iron.
Not So Healthy Forms of Soy
Fermented soy and tofu are good sources of vitamins and protein. Eating these foods and even unfermented tofu in moderation is safe for most people and may offer some health benefits. Yet, not all soy is created equal. At most grocery stores you’ll find a growing collection of “second generation” soy products designed to take the place of meat. You’re probably familiar with soy-based veggie burgers, “chicken” nuggets, “meat” crumbles, soy deli meats, and soy cheeses. Most of these foods are highly processed and contain a long list of fillers and additives. Less processed is soy milk, which is fortified with vitamins and minerals.
Other Types of Tofu
You’re probably familiar with the blocks of tofu you buy at the grocery store, available in soft, firm, and extra-firm, as well as silken tofu that has the consistency of a thick liquid. Silken tofu is best for making puddings and smoothies. What you’re probably less familiar with is black tofu, so-named because it’s made from black soybeans. In reality, black tofu is white with black specks scattered throughout from the black soybeans. It’s distinctive because black soybeans are higher in antioxidants, giving black tofu a health edge. You can also buy sprouted tofu at some grocery stores.
Soy Foods and Isoflavones
One distinction that makes soy foods unique is they contain an abundance of isoflavones, compounds that account for the anti-thyroid or goitrogen activity of unfermented soy. Isoflavones have both weak estrogenic and anti-estrogenic activity. Some research suggests soy foods help with menopausal hot flashes due to their weak estrogen-like activity.
Over the years, research has looked at the effect isoflavones have on breast tissue. Cultures who consume a lot of soy-based foods tend to have a lower incidence of breast cancer, possibly due to the weak estrogen effects that isoflavones have. By binding to estrogen receptors in the breast, they can block the activity of stronger estrogens on breast tissue. In lab and animal research, some studies suggest soy isoflavones have a stimulatory effect on cancer cells, but most human studies show soy DOESN’T accelerate breast cancer growth and may actually be protective, especially if you eat soy foods during childhood.
Are Soy Foods Heart Healthy?
For years, soy was labeled a heart-healthy food, primarily based on its ability to lower cholesterol. Yet, more recently, the FDA has reconsidered its stance that soy significantly lowers cholesterol after studies showed the drop in cholesterol is modest. Still, eating soy foods seems to improve endothelial function, the ability of blood vessels to relax. Improvements in endothelial function are favorable in terms of cardiovascular health. So, the verdict is still out on whether soy foods, fermented or unfermented, lower the risk for heart disease. Most likely, they have a modest benefit.
The Bottom Line
At the very least, soy foods are a good source of protein, B-vitamins, and calcium and they may offer some protection against heart disease and breast cancer. Stick with unprocessed forms of soy such as miso, tempeh, and moderate amounts of tofu and leave the highly processed, packaged products on the shelf. If you have thyroid disease or breast cancer, talk to your doctor before eating lots of soy foods and don’t take a soy or isoflavone supplement.
Today’s Dietician. Vol. 17. No. 4, p. 22.
The Journal of Clinical Endocrinology and Metabolism. The Effect of Soy Phytoestrogen Supplementation on Thyroid Status and Cardiovascular Risk Markers in Patients with Subclinical Hypothyroidism: A Randomized, Double-Blind, Crossover Study. February 2011.
J Nutr. 2010 Dec; 140(12): 2322S-2325S. Published online 2010 Oct 27. doi: 10.3945/jn.110.123802.
Circulation, 2006. 113(7): p. 1034-44.
Menopause, 2012. 19(7): p. 776-90.
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