When I was growing up in Chicago, my parents did what they could to enrich my urban experience by getting me out into nature from time to time. Twice a year, my family would head to nearby Rockford, Illinois, to spend some time with our friends the Funderburgs. The Funderburgs' four boys, my sisters, and I would construct forts in the hayloft in summer and go snowmobiling through the fields in winter. When I was old enough to wonder about such things, I asked Mr. Funderburg what it was that he grew on his farm. "Mostly soybeans," he told me.

    I'd never heard of the things. I come from a long line of professional meatpackers, and in Chicago-even among laypeople-eating beef or pork for breakfast, lunch, and dinner is even more endemic to our municipal culture than devotion to the Cubs.

    Since those carnivorous days in the 1970s, soy foods have gone from a niche product for the vegetarian-environmentalist crowd to a four-billion-dollar-a-year food industry. Soy is now on nearly every sushi bar menu （edamame） and is used as a vegetable oil, as a meat and dairy substitute, and as an inexpensive additive to increase the volume and improve the texture of many processed foods. The legume is so ubiquitous that it has found its way into everything from peanut butter to canned tuna. Many studies have shown the possible health benefits of eating soy, so most people consider it a "health food." After all, it's high in protein and has zero cholesterol-what could be wrong with that?

    Plenty, some say. Recent research has shown that soy may contain dangerous levels of isoflavones, natural chemicals that are similar to human estrogen. Isoflavones can affect fertility in men and may increase the incidence of breast cancer in at-risk women. Because of these concerns, the Israeli Ministry of Health has had a warning in effect since 2005. According to reports, the ministry suggests that adults moderate their soy consumption, that infants be given soy formula only when breast milk or cow's milk is not an option, and that parents limit the amount of soy their children eat. Health officials in France and Great Britain are concerned, too. French food manufacturers have been asked to reduce the isoflavones in soy formula, and are required to put warning labels on soy foods. The British Dietetic Association has warned parents against using soy formula during the first six months of a baby's life.

    Not surprisingly, the Soyfoods Association of North America doesn't necessarily agree with these concerns. Nancy Chapman, the group's executive director, says that the Israeli Ministry of Health's warning was largely based on research that used rats, whose hormonal makeup and reproductive system don't accurately predict what may happen in the human body.

    "Every time a study comes out that the soy industry doesn't like, they respond in one of two ways: It's poorly designed, or it's old," says Kaayla T. Daniel, Ph.D., a nutritionist and author of The Whole Soy Story. "Israel had a committee of more than a dozen distinguished nutritionists, researchers, pediatricians, and toxicologists who looked at the body of evidence, and concluded there was a risk."

    Daniel is one of an increasingly vocal group of nutritionists and scientists who are concerned about the possible risks of consuming too much soy. "The soy industry can never prove safety," she tells me. "They'll trot out studies showing a benefit, and act as if all the others indicating a risk are not a problem."

    About a decade ago, Daniel says, some of her clients began complaining about digestive problems, thyroid problems, and allergies they hadn't had before. She says each of them had suddenly increased the amount of soy in his or her diet. It just so happens that soy's reputation as a healthful alternative to animal protein was gaining traction around this time. In 1999, the Food and Drug Administration began allowing companies to claim that foods with soy protein "may reduce the risk of heart disease." This claim was based on early research that showed that soy protein could lower "bad" LDL cholesterol levels.

    Later studies were less conclusive-and the amount of soy protein consumed to reap the benefit would have to be the equivalent of 1.5 pounds of tofu or half a gallon of soy milk a day. As a result, in 2008 the American Heart Association recommended that the FDA rescind the health claim. Linda Van Horn, Ph.D., professor of preventive medicine at the Northwestern University Feinberg School of Medicine and chair of AHA's Nutrition Committee, says the quality and quantity of studies on soy and heart health have improved tremendously since the claim was first made. "When we looked at all the evidence, we didn't see enough to support the claim that soy is a blood-cholesterol-lowering agent," she says.

    Muddying the waters further are scientific studies that have reached very different conclusions. Soy can reduce the risk of breast cancer （Journal of the National Cancer Institute, 2006）; it has no effect （Cancer, 2007）; it can actually increase the risk （Cancer Research, 2001）; soy can help memory in postmenopausal women （Menopause, 2003）; no, it can't （Journal of the American Medical Association, 2004）.

    What is clear today, according to the Harvard School of Public Health, is that when it comes to soy and health, "some of the claims…go far beyond the available evidence." The AHA still says that it's perfectly fine to eat soy as part of a varied diet, and Van Horn continues to recommend soy to some of her patients, and to eat it herself.

    So what's the bottom line? If you're a woman who has been diagnosed with or has a family history of breast cancer, it's probably safest to avoid soy. Men hoping to father children should probably limit the amount of soy they eat, and parents would be advised to follow the Israeli guidelines in serving soy foods to their kids, especially infants and toddlers.

    That's what our family is doing （even though we're done having kids, thank you very much）. Because ironically-or perhaps not-my two young daughters （descendants of meatpackers, mind you） have never eaten meat. My wife and I had relied heavily on soy products early in the girls' lives, so I freaked out when I first learned of the health problems they might cause. We've since expanded our menus to include other vegetarian protein sources like lentils, black beans, and black-eyed peas. But there's still room for some soy. We just check ingredients to avoid the food products that it's sneaking into and buy organic whenever possible. As with most things in the health arena, moderation is key. Even Kaayla Daniel agrees. "Miso soup, tempeh, occasional tofu-the old-fashioned, whole soy products eaten modestly-are nourishing foods, and there's little risk to them," she says.

    Let It Ferment

    When it comes to soy and health, there isn't much consensus. But there is one thing that both the anti- and pro-soy camps seem to agree on: Fermented soy is good for you.

    The fermentation process alters the chemical makeup of soy, which reduces the level of potentially harmful isoflavones （plant estrogens）. Scientific studies have found that non-fermented soy foods （soybeans, soy powder） have as much as three times the isoflavones as the fermented stuff.

    Fermented soy foods include soy sauce and miso, which is most commonly associated with miso soup. Vegetarians will recognize tempeh, a fermented soybean cake that is often used in place of meat.

    More adventurous eaters might consider adding natto-somewhat stinky fermented soybeans-to their diets. One study suggests that an enzyme in natto might be effective in battling Alzheimer's disease. Researchers theorize that the enzyme may be able to break up the protein that forms the memory-altering deposits on the brain.

    小时候我在芝加哥的时候，我的父母尽最大的可能让我增长对城市的了解，他们总是时不时地带着我到大自然里去。每年我们家人会去两次离我们这里不远的伊利诺伊州的罗克福德，和我们的朋友范德伯格一家呆段时间。夏天的时候范德伯格家的四个孩子、我妹妹和我会在谷仓里建城堡，冬天的时候我们会坐着雪橇穿过田野。我大一些开始会思考事情后，问范德伯格先生他们家的农场里主要种些什么。他告诉我说："大部分是大豆。"

    我从来没听说过这种事。我生活的那个城市有专业的肉类加工业，在芝加哥--即使是在信徒之间--一日三餐吃牛肉或者猪肉是我们的城市文化，甚至比对小熊队还要忠诚。

    从二十世纪70年代的食肉年代开始，大豆食品已经从素食环保主义者的特殊用品成长为了一个年产值有40亿美元的产业。现在几乎每家寿司店的菜单上都有大豆，大豆可以做植物油，可以代替肉类和奶制品，作为价格便宜的食品添加剂，还可以改善很多加工食品的口感。豆类可以说是无处不在，从花生酱到金枪鱼罐头，里面都有它们的踪迹。很多研究表明食用大豆可能对健康有益，因此大多数人认为大豆是一种"健康食品".毕竟，大豆的蛋白质含量很高，并且胆固醇的含量几乎为零--这还能有错吗？

    要多吃大豆，有些人说。最近有研究表明，大豆含有的大豆异黄酮量可能会对人有伤害，这是一种和人类雌激素类似的天然化学物质。异黄酮可能会影响男性生育能力，并可能增加高危妇女乳腺癌的发病率。由于存在这些问题，以色列卫生部实际上从2005年就发出有关警告。据报道，该部建议成年人应适度食用大豆，而对于婴儿，只有在没有母乳和牛奶的情况下才能吃豆制品，此外，父母要控制孩子食用大豆的量。法国和英国的卫生办公室对该问题也很关注。法国食品生产商已被要求降低大豆食品中的异黄酮含量，并被要求在大豆食品的包装上打出警告标签。英国营养协会已经警告父母不要给6个月前的婴儿喂食大豆制品。

    北美的Soyfoods协会并不同意这一观点。这毫不奇怪。该协会主管南希查普曼说，以色列卫生部的警告主要是建立用老鼠做实验的基础上，老鼠的激素组成和生殖系统并不能准确的预测出异黄酮对人体内的影响。

    营养学家、《The Whole Soy Story》的作者Kaayla T. Daniel博士说："每次有大豆制品行业不喜欢的研究公布时，他们回应的方式都是那么两种：要么是设计不当，要么就是用的大豆是陈的。以色列的卫生委员会有十几位杰出的营养师、研究人员、儿科医生、毒物学家，他们对人体进行研究，然后得出了大豆可能存在危险的结论。"

    丹尼尔是一个名声鹊起的营养学家和科学家团队中的一员，他们担心使用过量大豆可能会对人造成危害。她告诉我说："大豆行业永远不能证明其安全性。他们会对外宣扬那些能够给他们带来利益的研究，表现的好像是别人提出的所有风险都不是问题。"

    丹尼尔说，大约十年前她的一些客户开始抱怨消化问题、甲状腺问题、过敏，这些毛病他们以前都没有。她说这些客户都是突然在自己的饮食中增加了大量的黄豆。那时候正好盛传黄豆是肉类的健康替代品，吸引了很多人。1999年，美国食品和药物管理局开始允许食品公司声明含有大豆蛋白的食品"可能会降低患心脏病的风险".这一声明是基于早期的研究结果，这些结果表明大豆蛋白可以降低人体内"坏"的低密度脂蛋白胆固醇的水平。

    后来的研究就没有那么有说服性了--要获得人体所需能量所需消耗的大豆蛋白的量相当于每天吃1.5磅豆腐或半加仑豆奶。因此，2008年美国心脏协会建议美国食品及药物管理局撤销该健康声明。琳达范霍恩博士是美国西北大学范伯格医学院的预防医学教授、美国心脏协会营养委员主席，她说自从该声明提出后，关于大豆与心脏病关系的研究无论是质量和数量都有极大的提高。"我们看到这些研究证据时，没觉得这些结果就能够证明大豆能够降低血液中的胆固醇含量。"她说。

    让人更迷惑的是科学研究的结果都各不相同。大豆可降低患乳腺癌的风险（美国国立癌症研究院杂志，2006年）;它对乳腺癌没有任何影响（癌症，2007年）;它实际上会提高乳腺癌的患病率（癌症研究，2001年）;大豆可帮助提高绝经后妇女的记忆力（更年期，2003年）;大豆不可能提高绝经后妇女的记忆力（美国医学协会，2004年）.

    哈佛大学公共卫生学院说，现在唯一可以确定的就是每当涉及到大豆和保健时，"一些声明……远远超过了实际能够得到的结果的范围".美国心脏学会表示，将黄豆作为众多饮食中的一种是很好的，范霍恩也继续建议她的一些患者们吃黄豆，她本人也吃黄豆。

    那么底线是什么呢？如果你是一个女人，并被诊断患有乳腺癌或有乳腺癌家族史，那么最好避免吃黄豆。而如果是男人，又想做父亲，那么最好控制饮食中黄豆的量，而父母，或许应该考虑按照以色列的指导方针，限制孩子饮食中大豆的量，特别是婴幼儿。

    我们家就是这样（虽然我们已经有了孩子，但还是非常感谢你们）.因为很具讽刺意味的是--或许也没有吧--我的两个小女儿（注意，是两个肉食主义者的后代）还从来没吃过肉。我妻子和我在孩子小的时候严重依赖豆制品，所以当我第一次知道豆制品可能会带来的健康问题时吓了一大跳。我们现在已经扩大了我们的菜单范围，以便获得植物蛋白，比如小扁豆、黑豆、豇豆。但仍旧包括一定量的大豆。我们只是检查食物的成分以避免它们存在我们不知道的危险，并且尽最大可能买有机食物。就像卫生领域的其他大多数事情一样，重点是要适度。Kaayla Daniel也同意这一观点。她说："酱汤、豆豉、老式豆腐，所有这些豆制品都应该适当食用，这些食品都是滋补食品，并不存在太大的风险。"

    让它发酵

    说到大豆和健康，意见总是不统一。但是有一件事似乎是支持方和反对方都同意的，发酵后的大豆对人身体有好处。

    发酵工艺会改变大豆的化学组成，从而降低有害异黄酮（植物雌激素）的含量。科学研究已经发现，未发酵的大豆食品（大豆、大豆粉）含异黄酮的量是发酵后的3倍之多。

    发酵型大豆食品包括酱油和大豆酱，这是做酱汤最常用的佐料。这是最常见的与酱汤。素食者们以后将会认可豆豉，这是一种经常用来代替肉类的发酵豆粕。

    更具冒险精神的人们还可以考虑吃些纳豆--有股恶臭味的豆酱。一项研究表明，纳豆中的一种酶或许可以有效地对抗阿尔茨海默氏症。研究人员推论说，研究人员推论说，这种酶可以破坏积存在大脑中的造成记忆改变的蛋白质。