Now that a recent widely reported Harvard study concluded that red meat consumption shortens lives, should you be eating more plant-based sources of protein such as tofu?
Maybe yes, maybe no. As with many things in nutrition, it’s not a simple thing to decide. But, after reading about tofu nutrition facts, you can choose for yourself whether you want to include it in your diet.
Soy products, the second largest cash crop in the country, valued at $31 billion a year, contain antioxidant compounds called isoflavones, which are chemically similar to estrogen. It is these phyto- (plant) estrogens that have caused controversy in the nutrition world.
Advocates of a rich soy-based diet say that products like tofu can:
reduce the risk of developing certain cancers
reduce the likelihood of developing cardiovascular disease (CD)
heal hot flashes
Several research studies on soy's efficacy have been inconclusive. One study published in the American Association for Cancer Research failed to conclude any link between increased tofu consumption and lowered risk of prostate cancer.
The Journal of the National Cancer Research Institute published a Johns Hopkins University study concluding that it would be premature to recommend high isoflavone intake to prevent breast cancer or the recurrence of it.
Women experiencing undesirable side effects from menopause such as hot flashes are frequently urged to eat more tofu and other soy products to make up for the lost estrogen. But a University of Miami study shows that soy does not necessarily help women during menopause.
So where does the truth lie?
Like almost everything else in life, somewhere in the middle. Eating a lot of highly processed soy products (soy cheese, soy hot dogs, soy burgers) could potentially activate too many estrogen receptors in the body.
But eating a moderate amount of unprocessed tofu can be part of a balanced, nutritious, whole-food diet (say, a quarter of a block of tofu or fermented tempeh, or a small cup of edamame).
Soy proponents (especially marketers advertising it as a super food) say that products like tofu contain isoflavones that are potent antioxidants.
University of Washington professor Michael E. Rosenfeld, a nutrition researcher who focuses on the role of antioxidants and cardiovascular disease, recommends including tofu in the diet. But he admits that the role of soy as a powerful antioxidant capable of killing free radicals in human cells is still ambiguous.
Rosenfeld co-authored a study that concluded that genistein, the main isoflavone found in tofu, does not prevent arteriosclerosis (hardening of the arteries).
"We administered genistein to mice that developed cardiovascular disease (CD). The isoflavone supplement did not prevent progression of CD in older mice," says Rosenfeld, who also co-authored another study that found that the benefits of antioxidant supplements are also inconclusive, at best, and completely nonexistent, at worst.
Rosenfeld believes that tofu offers the full complement of compounds that cannot be derived from isoflavone supplements (similar to whole-food antioxidants being more effective, possibly, than antioxidant supplements).
But if you're in the winter of your life, Rosenfeld says that starting to eat tofu now likely won't help. The earlier that one consumes tofu in life, says Rosenfeld, the better.
"Up until now, there have been no studies that whole sources of soy, like tofu, can prevent or cure CD [cardiovascular disease]. The key is that CD markers can begin to develop in childhood. Foods like tofu really need to be consumed over a lifetime; CD will not be reversed if you start eating tofu at 50 years old."
What's in a serving of tofu?
One half-cup of tofu contains 10 grams of protein; 25 percent of the daily recommended value of calcium; 11 percent of iron; 5 grams of fat (mostly polyunsaturated, omega-6 fatty acids). One serving of tofu is relatively high in other minerals such as phosphorous, magnesium, copper, selenium, and especially manganese (40 percent of daily recommended value).
Because tofu also contains the aforementioned estrogen-like isoflavones, this brings up a common question amongst those paranoid to partake in soy and tofu.
Will men develop female characteristics if they eat tofu?
Rosenfeld unambiguously and emphatically says, "You’re not going to grow breasts if you eat tofu!"
In the studies he co-authored on genistein, Rosenfeld says, "Markers of effects that would represent estrogen receptor mediated responses were examined and nothing popped out in the study; there's nothing to worry about. You’d have to be taking huge amounts of purified phytoestrogen to have a huge impact."
The bottom line on tofu, according to Rosenfeld: it's a great source of protein for vegetarians and even carnivores should eat more of it.
"The more we can reduce our red meat intake, the better off we’ll be in the long run. People should replace red meat with other sources of protein such as tofu frequently. Consumption of red meat has been linked to multiple forms of cancer and elevated bad blood cholesterol from high saturated fat intake.
Is tofu really a healthier source of protein than red meat?
Not necessarily, according to Kaayla Daniel, a Ph.D. in nutritional sciences and anti-aging therapies, and author of the book "The Whole Soy Story: The Dark Side of America's Favorite Health Food."
"Eating tofu every day could lead to problems," says Daniel. "If someone has a whole block of tofu at dinner and has a cup of soy milk for cereal and snacks on a whole bag of soybeans and eats a soy meal replacement bar, that amounts to a whopping amount of plant estrogens."
The problem with eating a diet rich in plant estrogens, says Daniel: "They may be weaker than human estrogens but nonetheless, they do affect the body's ability to use and make estrogen."
Yet Daniel acknowledges that tofu does have a place in a healthy eating plan, if it's incorporated into the diet similar to how traditional Asians eat it.
"The traditional way in Asia involves eating a couple small squares in miso soup or fish broth," says Daniel, who adds that the problem is in the U.S. is: "We’re not eating only a few cubes, we’re eating the whole block."
What are the risks of eating large amounts of tofu?
According to Daniel, a whole cup of tofu contains 56 mg of isoflavones. Consumed on a daily basis, Daniel believes the potential for thyroid damage (in the form of hypothyroidism, which produces a sluggish thyroid) is the most serious risk, followed by potential reproductive system damage.
"What I would suggest is don’t eat tofu every day and never eat processed soy products,” she says. “Eating veggie burgers or a whole big bag of edamame is bad; including unprocessed tofu twice a week in a stir-fry is not bad."
If eating a lot of tofu and red meat is bad, what's left ... chicken?
Daniel alludes to the previously mentioned Harvard study on red meat as "Nonsensical...[a] complete misuse of statistics, involving an observational study of unhealthy individuals, using notoriously fallible food frequency questionnaires that produced unwarranted conclusions."
For the omnivore, Daniel suggests that a small serving of humanely raised grass-fed beef offers a lot of nutritional density. But the bottom line, whether it's red meat, or tofu: moderation is the key.
Daniel recommends tofu that has no additives and avoiding pre-flavored block tofu. "Don't get duped by ingredients listed as 'natural flavorings,’” she says. “They are the same as 'artificial flavors.'"
Can tofu affect your brain?
Possibly. A study published in the Journal of the American College of Nutrition involving Japanese-American men living on Oahu concluded that higher midlife tofu consumption was associated with cognitive impairment and brain atrophy later in life.
Now that's food for thought.
The estrogen-laden moral of the story: soy nuggets and tofu dogs? Avoid. Small portions of fermented tempeh, a block of tofu, or a small bowl of edamame? Enjoy in good health.
What do you think about tofu? Do you think it's a super-food? Only if it's in moderation and unprocessed? Let us know in the comments below.
Judd Handler is a health writer for MNN.com. He lives in Encinitas, Calif.
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