Last year I did a webinar on vegetarian diets. I talked a bit about the convenience and nutritional benefits of soy foods like tofu and tempeh. Some attendees expressed fears about soy safety, because soy contains isoflavones that are chemically related to estrogenic hormones. There is scant evidence that soy intake increases disease risks, but that doesn’t quell the fears. It’s a shame, because there are plenty of other junky/worthless foods that should be on an “AVOID” list, not because they’re dangerous. Because they’re junk.
Soy foods have been used in Southeast Asia for centuries. Tofu, tempeh, soy sauce, miso, edamame and the like are dietary staples. You’d think that if these foods were so dangerous, the populations of all those countries would have been decimated by now.
Some of the popular fears:
- Soy increases breast cancer risk
- Soy disrupts male and female hormones
- Soy suppresses thyroid function
Association Does NOT Equal Causation
Since the late 20th century, health research has linked soy consumption with many health benefits:
- lower risk for heart disease
- lower blood pressure
- lower blood sugar
- improved fertility
- reduction of annoying menopause symptmons
- reduced risk for breast cancer
Thanks to growing fear of dairy (at that time) plus clever marketing by the soy industry, soy foods grew in popularity in Western countries, especially soy-based dairy substitutes and soy protein powder used in smoothies. Infants were increasingly fed soy formula. Soy protein is added to vegetarian burgers, cereals and energy bars. So soy became widespread in the food supply, but in very different forms from traditional Asian foods.
Studies linking soy consumption to health benefits may fall into the trap of “Association = Causation” syndrome. For example, let’s talk breast cancer risk. Women who consume more soy foods have lower risk for breast cancer. This is true in Southeast Asian countries, where soy foods have been widely consumed for centuries and breast cancer risk is lower compared to Western countries. A study in the U.S. on 6000 women with breast cancer found that the women who ate more soy foods were less likely to die from this cancer.
Conclusion? Soy prevents cancer or helps with cancer recovery? ?? Not So Fast. Women who eat more soy foods tend to have healthier diets in general and tend to weigh less. Obesity is a known risk for breast cancer and for cancer severity. Better conclusion: high intake of soy foods is a marker for a healthier lifestyle. At the moment, there isn’t any evidence that soy foods alone will reduce cancer risk.
Test tube experiments are not the same as the real world
This statement is true for hundreds, perhaps thousands, of nutrition studies, not just for soy. Isolating some nutrient or food component, and bombarding cells with this substance in a test tube doesn’t mimic what happens when you consume a food with that nutrient. Do you even absorb this substance? This depends on:
- Whether the substance is biologically available for absorption or must be metabolized to some other form first.
- That the form you consumed can be absorbed by your digestive system.
- That gut microbes don’t metabolize it into something else.
- That the food you ate doesn’t interfere with absorption or metabolism.
- That medications you take didn’t interfere.
- Even if this substance is absorbed into your blood, does it end up in the target tissues or organs?
Test tube experiments cannot duplicate this kind of very complex system.
All of these complications apply to soy foods. Lab experiments done with highly concentrated isoflavones that were extracted from soy may show some potentially adverse effect, but eating tofu is unlikely to create that same situation in your body.
Rats and Mice Are Not Humans
You might think that goes without saying, but not if you’re a researcher. Rats and mice are frequently used as some sort of human substitute in nutrition experiments. Rodents are easy to use. It’s easy to completely control their diets, plus they have a short lifespan. Rats might be fed whopping amounts of soy isolates, with questionable results. The headlines scream “Soy Causes [X disease]!” Well, in rats maybe. But rat metabolism and digestion are extremely different from humans, so how is this relevant?
Doing soy feeding experiments on humans would be impractical. Lock people up for years, feeding them diets with different levels of soy, measuring all possible health outcomes. Who would do that?
The example of soy consumption in Asian countries and health is probably our best real world human “experiment”. If soy increased risk for all those health problems — cancer, thyroid dysfunction, male hormone disruption — people in Eastern Asian countries would be suffering massive levels of ill effects. They are not.
There’s no reason you should consume soy foods, so if you’re afraid of them, you’re free to avoid them. I always prefer whole natural foods, so tofu, tempeh, soy sauce and miso are on my shopping list. I’m fine with edamame if someone else prepares it. Soy protein powders? No. Bars, cereals or “burgers” made with soy protein isolates? No. I don’t do soy milk or any of that stuff either.
5 good reasons to include soy foods in your diet
- High protein (and a plant-sourced food)
- High in fiber and other key nutrients
- Easy to use
- Linked to lower risk for many chronic diseases
- Linked to some benefits for menopause symptoms, bone health and other concerns of older women
I like to keep a package of tofu handy for easy vegetarian meals. I recently put together an Asian-style soup, a one-pot meal, with tofu and other items I had in the kitchen. Here’s the plan:
Noodle Tofu Vegetable Soup
I put this soup together with the ingredients I had available at the time. You can add more or less of none of some, add different ones, to your taste. Broccoli and sugar snap peas would work nicely, as would scallions and chopped spinach. Cook the noodles separately and keep them separate in a bowl, tossed with a bit of oil so they don't stick together.
- 4-6 oz soba or udon noodles
- peanut or canola oil
- 1 quart chicken or vegetable stock
- 1 block firm tofu, cut into chunks
- 2 cups chopped zucchini
- 1 chopped jalapeno
- 2 carrots, shredded
- 1 cup chopped mushrooms of choice
- 3 cloves garlic, minced
- 2 TB white miso
- salt to taste
- soy sauce
- toasted sesame oil
- rice wine vinegar
- Step 1 Cook the noodles according to package directions. Drain, put in a bowl and toss with a drizzle of oil to coat, to prevent sticking.
- Step 2 Heat the stock in a large sauce pan. Simmer the carrots, zucchini, mushrooms and jalapeno briefly, about 3 minutes. Add the garlic and tofu and heat through.
- Step 3 In a small bowl, mix the miso paste with 2-3 TB of the hot stock until the paste is dissolved. Add another 2-3 TB of stock and combine to eliminate any chunks of miso. Add this mixture back into the pot and stir thoroughly.
- Step 4 Season to taste with soy sauce, salt, sesame oil and vinegar.
- Step 5 To serve, put some noodles in a bowl and label soup over.