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 soy itself is unhealthy, 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 used mostly in processed foods as a less expensive 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 meats alternatives, 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 reduce 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.
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.
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.