Tempeh, a fermented soy food, is one of the most nutritious vegan sources of protein. If you've never tried it, this vegan Southwestern tempeh hash with sweet potatoes and kale is a great place to start!
When I started my undergraduate degree in nutrition, it was pretty much accepted that soy protein was a good thing. In 1999, the FDA had approved a health claim stating a diet low in saturated fat and cholesterol including soy protein is associated with a lower risk of heart disease. There was plenty of research to back it up – one meta-analysis of 34 studies found a 13% decrease in unhealthy LDL cholesterol associated with soy protein consumption.
But by the time I graduated in 2007, a full blown nutrition controversy was brewing. That same year, a group of scientists petitioned the FDA to reverse this claim, so the FDA agreed to reevaluate. A year earlier, the American Heart Association reversed it’s position on soy protein and cholesterol lowering (although they still endorsed soy products as a low saturated fat protein source). Most argued that soy protein did not significantly lower cholesterol enough to warrant a claim. Others claimed
, linking it to food allergies, breast cancer, weight gain and thyroid disease.
So what’s the truth about soy? Weeding through the many conflicting studies is complicated, but most of the inconsistency in research results can be explained by the difference in the way soy is consumed in Asia versus the United States. Most of the initial research indicating a benefit from soy was conducted in Asia, where soy is consumed in an unprocessed or minimally processed form. It's often fermented, a process that makes the nutrients more absorbable. Here in the states, despite being a country of tofu-phobics, we actually consume a huge quantity of soy, usually in a highly processed form. Soybean oil is ubiquitous with processed, junk foods, a cheap alternative to the butter, olive oil and other fats used in home cooking. Soy proteins, like textured vegetable protein and soy protein isolate are found not just in fake meats, but hidden in nutrition shakes, protein bars, canned soups, and condiments.
The soybean itself is a nutrient rich food. Soybeans contain vitamins like vitamin K and B vitamins. Soybeans are mineral rich, with iron, phosphorus, copper and potassium. They even have a pretty decent dose of omega 3 fats. And there's plenty of research showing soy can be of benefit in the prevention of chronic disease.
Most heart healthy benefits of soy are the result of being a plant-based substitute for meat and other animal foods. But soy also contains a phytonutrient called soyasaponin, which helps prevent lipid oxidation in blood vessels and reduce the absorption of cholesterol in the gut.
Soy and cancer prevention is controversial topic. Most of the confusion has to do with the estrogen-like effect of isoflavones, a compound found in high quantities in soy. Excess estrogen has been linked to cancer, especially breast cancer, so on the surface, you would think something similar to estrogen would have similar, cancer-promoting effects. But estrogen is about 1,000 times stronger than the isoflavones found in soy. Isoflavones may actually
the risk of estrogen dependent cancers by blocking estrogen receptors in cells. The anticancer benefit of soy seems to be especially powerful in fermented soy foods, like tempeh, which are more concentrated in genistein, a substance that kills cancer cells.
Probiotics When soy is consumed in a fermented form, as in tempeh, miso and natto, soy is an excellent source of probiotics, healthy bacteria that aid in digestion, promote nutrient absorption and enhance immunity. Recent studies have also linked a healthy intestinal flora to a reduced risk of colon cancer, inflammatory bowel disease and even obesity.
The key with soy is to choose the least processed versions, preferably fermented. The more processed a soy product it is, the less beneficial compounds it contains. Look for organic soy, since the vast majority of conventional soy is grown from genetically modified seeds, a practice that's incredibly harmful for the environment.
Unsure of what soy foods are best? Let's look at common soy foods.
TEMPEH // Tempeh is made from fermented soy beans that are pressed into a cake. It has a crumbly texture and a stronger flavor than tofu. Personally, tempeh is my favorite soy product, for taste, nutrition and versatility.
TOFU // Made from soy milk in a process similar to how mozzarella cheese is made. It's minimally processed, high in calcium, and soaks up the flavor of whatever delicious sauce you cook it in.
MISO // A Japanese condiment made by fermenting salted soybeans, rice and/or barley, resulting in a thick paste used to make soup, sauces and marinades.
NATTO // So, I've never tried natto, whole fermented soybeans, but it looks disgusting. It's described as having a slimy texture and strong flavor - not the most appealing description. But it's really good for you, so feel free to give it a try if you're feeling adventurous!
SOY SAUCE // Soy sauce is a condiment traditionally made by fermenting a paste of soybeans and grains in a brine. The resulting liquid is soy sauce. Unfortunately, some producers make it from hydrolyzed soy protein, rather than fermentation. In fact, some of these mass produced soy sauces imported from Asia were found to be contaminated with a carcinogenic chemical called 1,3-DCP. Look for fermented soy sauce which is labeled naturally brewed or naturally fermented.
SOY MILK // Fresh soy milk is made by blending soybeans and water and filtering out the solids. A lot of the soy milk found in stores isn't fresh soy milk, but is made from processed soy protein rather than whole soybeans. Soy milk often contains large quantities of added sugar and the controversial ingredient careegnan. If you're going for a non-dairy milk, go for unsweetened almond milk or coconut milk, which I think tastes much better too.
SOY PROTEIN // Soy protein, in the form of textured vegetable protein, hydrolyzed soy protein and soy protein isolate, is a heavily processed form of soy. Look for these ingredients in meat substitutes (i.e. soy dogs, soy burgers, soy bacon), foods marketed as high protein, like protein shakes, and hidden in many (and sadly most) other processed foods.
SOYBEAN OIL // Being high in unsaturated fat, you would think soybean oil is a heart healthy choice. However, most of the fat in soybean oil is polyunsaturated, with very little omega 3s. Although polyunsaturated fat does not seem to negatively affect cholesterol, recent research has linked it to an increased risk of heart disease.
Vegan Southwestern Hash
Adapted from Martha Stewart Meatless
- 4 small sweet potatoes, diced in 1/2-inch cubes
- 1 chipotle pepper in adobo, minced plus 2 teaspoons adobo sauce
- 8 ounces tempeh, crumbled
- 1 tablespoons coconut oil, avocado oil or olive oil
- 1 clove garlic, minced
- 1/2 teaspoon cumin
- 4 handfuls of chopped, stemmed kale
- 2 tomatoes, seeded and diced
- 3 scallions, sliced
- 1 14-ounce can black beans, drained and rinsed
- 1 tablespoon nutritional yeast
- Salt and black pepper to taste
- 1 avocado, diced
- 1 lime, sliced
- Bring a large pot of water to a boil. Add sweet potatoes and boil until mostly tender, about 10 minutes.
- Toss together crumbled tempeh and adobo sauce, set aside.
- Heat 1 tablespoons oil in a large skillet on medium-high heat. Add potatoes. Cook without moving for a few minutes, then flip with a spatula. Continue to cook, flipping with a spatula every few minutes or so, until browned and tender. Stir in garlic and cumin and cook an additional 30-60 seconds until fragrant. Add kale. Cook 2 minutes until mostly wilted. Add tomatoes and scallions. Cook another 2 minutes until tender. Stir in black beans, reserved marinated tempeh and cook until warmed through, about 1-2 minutes.
- Remove from heat, season with salt and pepper to taste. Stir in nutrition yeast and avocado.
- Serve with lime slices if desired.