Preventive Medicine Column
Dr. David L. Katz
Some months ago, a reader – 36-year-old wife and mother of two young children- asked me to address the health effects of soy, and I promised I would. Specifically, she posed her concern this way:
What I’ve been reading lately about the safety of soy, especially processed soy products (e.g. soy lunch meat, soy hot dogs, veggie burgers, soy bacon) concerns me. I’m concerned about these products for me and my husband but especially for my children who are obviously still growing and developing. I’m trying to transition out of the more processed products but my son is very picky to begin with and is putting up a fight. I’ll switch him to meat if that is healthier but I want to know if what I read on the internet is valid.
Time for me to keep my promise, and I owe the timing to a Harvard study, just published in the Annals of Internal Medicine, showing higher mortality in men and women who consumed a meaty, Atkins-like diet. Because while there is some beefing to do about soy, my bigger beef is with…beef. So, no, mom-of-two, don’t switch to meat. And yes, overall, soy is safe.
Of course, the soy story is a bit complicated- or the question would not have been posed in the first place. Soy is a complex food, and among its many constituents are phytoestrogens, estrogen-like plant chemicals. Some of the concern about soy derives from animal studies showing increased cancer risk with high-dose exposure. Additional concern derives from potential associations between the wide array of processed soy products – the likes of soy cheese and even soy protein isolate, an alias for MSG- and adverse health outcomes, from cancer to thyroid disease.
Overall, there is considerable reassurance in an evidence review on the topic conducted by the Agency for Healthcare Research and Quality (http://www.ahrq.gov/clinic/epcsums/soysum.htm). No convincing evidence of adverse health effects in humans of soy consumption was found.
However, the evidence for benefit was largely inconclusive as well. Among the likely explanations for this is that in the U.S., we do, indeed, tend to eat a lot of processed soy foods- which, of course, contain many ingredients other than soy. Some of these- including the customarily copious additions of sugar and salt- may be the bad actors that implicate soy by association.
Traditional Asian diets that include a lot of soy generally do so in the form of minimally processed, whole or fermented soy foods, such as miso, tempeh, tofu, soy milk, and edamame. The Asian societies eating these foods routinely are among the healthiest and longest-lived on the planet. I, and the colleagues I most respect, are all convinced that such foods can confer a meaningful health benefit here as well.
The take-away about soy, then, is courtesy of Aesop: it is best judged by the company it keeps. Soy is, in general, a very healthful food. But processing mischief can undo the native goodness of soy, as it does in other food categories. Choose wisely.
But don’t choose more meat.
The recent Harvard study in more than 120,000 people found that those who, over time, ate more of their calories from animal sources and fewer of them from plants were more likely to get sick and die prematurely. Admittedly, an observational study of this type does not prove cause and effect. But when, in over 100,000 people, A seems to cause B, and there is a plausible mechanism, and other likely explanations have been considered and eliminated — the most logical conclusion is that A likely does cause B, until or unless a better explanation is found.
Even without this study, we had ample cause to resist any carnivorous inclinations. A meaty, Atkins-type diet is bad for the animals that are mass-produced inhumanely to be turned into food; bad for the planet that is mightily abused on and near industrial farms; and convincingly bad for human health. Yes, our Stone Age ancestors ate meat, but they did not get it at McDonald’s! They ate lean, wild animals that have very little in common with meatballs, McNuggets, or pastrami. If you are inclined to eat meat you secure with a bow and arrow, I withhold most of my objections.
Eating well generally means choosing wholesome, pronounceable foods direct from nature whenever possible. Lean meats can fit in here; bacon cheese-burgers and deli meats do not. But this real estate is much dominated, if not owned, by plant foods, soy among them.
Perhaps one of the reasons measuring health benefits of soy in the lab proves elusive is because soy-eating populations derive considerable benefit not only from what they are doing, but from what they aren’t doing. They aren’t eating much meat.
Dr. David L. Katz; www.davidkatzmd.com