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.

    小時候我在芝加哥的時候，我的父母盡最大的可能讓我增長對城市的了解，他們總是時不時地帶著我到大自然里去。每年我們家人會去兩次離我們這里不遠的伊利諾伊州的羅克福德，和我們的朋友范德伯格一家呆段時間。夏天的時候范德伯格家的四個孩子、我妹妹和我會在谷倉里建城堡，冬天的時候我們會坐著雪橇穿過田野。我大一些開始會思考事情后，問范德伯格先生他們家的農場里主要種些什么。他告訴我說："大部分是大豆。"

    我從來沒聽說過這種事。我生活的那個城市有專業(yè)的肉類加工業(yè)，在芝加哥--即使是在信徒之間--一日三餐吃牛肉或者豬肉是我們的城市文化，甚至比對小熊隊還要忠誠。

    從二十世紀70年代的食肉年代開始，大豆食品已經從素食環(huán)保主義者的特殊用品成長為了一個年產值有40億美元的產業(yè)�，F在幾乎每家壽司店的菜單上都有大豆，大豆可以做植物油，可以代替肉類和奶制品，作為價格便宜的食品添加劑，還可以改善很多加工食品的口感。豆類可以說是無處不在，從花生醬到金槍魚罐頭，里面都有它們的蹤跡。很多研究表明食用大豆可能對健康有益，因此大多數人認為大豆是一種"健康食品".畢竟，大豆的蛋白質含量很高，并且膽固醇的含量幾乎為零--這還能有錯嗎？

    要多吃大豆，有些人說。最近有研究表明，大豆含有的大豆異黃酮量可能會對人有傷害，這是一種和人類雌激素類似的天然化學物質。異黃酮可能會影響男性生育能力，并可能增加高危婦女乳腺癌的發(fā)病率。由于存在這些問題，以色列衛(wèi)生部實際上從2005年就發(fā)出有關警告。據報道，該部建議成年人應適度食用大豆，而對于嬰兒，只有在沒有母乳和牛奶的情況下才能吃豆制品，此外，父母要控制孩子食用大豆的量。法國和英國的衛(wèi)生辦公室對該問題也很關注。法國食品生產商已被要求降低大豆食品中的異黃酮含量，并被要求在大豆食品的包裝上打出警告標簽。英國營養(yǎng)協會已經警告父母不要給6個月前的嬰兒喂食大豆制品。

    北美的Soyfoods協會并不同意這一觀點。這毫不奇怪。該協會主管南希查普曼說，以色列衛(wèi)生部的警告主要是建立用老鼠做實驗的基礎上，老鼠的激素組成和生殖系統并不能準確的預測出異黃酮對人體內的影響。

    營養(yǎng)學家、《The Whole Soy Story》的作者Kaayla T. Daniel博士說："每次有大豆制品行業(yè)不喜歡的研究公布時，他們回應的方式都是那么兩種：要么是設計不當，要么就是用的大豆是陳的。以色列的衛(wèi)生委員會有十幾位杰出的營養(yǎng)師、研究人員、兒科醫(yī)生、毒物學家，他們對人體進行研究，然后得出了大豆可能存在危險的結論。"

    丹尼爾是一個名聲鵲起的營養(yǎng)學家和科學家團隊中的一員，他們擔心使用過量大豆可能會對人造成危害。她告訴我說："大豆行業(yè)永遠不能證明其安全性。他們會對外宣揚那些能夠給他們帶來利益的研究，表現的好像是別人提出的所有風險都不是問題。"

    丹尼爾說，大約十年前她的一些客戶開始抱怨消化問題、甲狀腺問題、過敏，這些毛病他們以前都沒有。她說這些客戶都是突然在自己的飲食中增加了大量的黃豆。那時候正好盛傳黃豆是肉類的健康替代品，吸引了很多人。1999年，美國食品和藥物管理局開始允許食品公司聲明含有大豆蛋白的食品"可能會降低患心臟病的風險".這一聲明是基于早期的研究結果，這些結果表明大豆蛋白可以降低人體內"壞"的低密度脂蛋白膽固醇的水平。

    后來的研究就沒有那么有說服性了--要獲得人體所需能量所需消耗的大豆蛋白的量相當于每天吃1.5磅豆腐或半加侖豆奶。因此，2008年美國心臟協會建議美國食品及藥物管理局撤銷該健康聲明。琳達范霍恩博士是美國西北大學范伯格醫(yī)學院的預防醫(yī)學教授、美國心臟協會營養(yǎng)委員主席，她說自從該聲明提出后，關于大豆與心臟病關系的研究無論是質量和數量都有極大的提高。"我們看到這些研究證據時，沒覺得這些結果就能夠證明大豆能夠降低血液中的膽固醇含量。"她說。

    讓人更迷惑的是科學研究的結果都各不相同。大豆可降低患乳腺癌的風險（美國國立癌癥研究院雜志，2006年）;它對乳腺癌沒有任何影響（癌癥，2007年）;它實際上會提高乳腺癌的患病率（癌癥研究，2001年）;大豆可幫助提高絕經后婦女的記憶力（更年期，2003年）;大豆不可能提高絕經后婦女的記憶力（美國醫(yī)學協會，2004年）.

    哈佛大學公共衛(wèi)生學院說，現在唯一可以確定的就是每當涉及到大豆和保健時，"一些聲明……遠遠超過了實際能夠得到的結果的范圍".美國心臟學會表示，將黃豆作為眾多飲食中的一種是很好的，范霍恩也繼續(xù)建議她的一些患者們吃黃豆，她本人也吃黃豆。

    那么底線是什么呢？如果你是一個女人，并被診斷患有乳腺癌或有乳腺癌家族史，那么最好避免吃黃豆。而如果是男人，又想做父親，那么最好控制飲食中黃豆的量，而父母，或許應該考慮按照以色列的指導方針，限制孩子飲食中大豆的量，特別是嬰幼兒。

    我們家就是這樣（雖然我們已經有了孩子，但還是非常感謝你們）.因為很具諷刺意味的是--或許也沒有吧--我的兩個小女兒（注意，是兩個肉食主義者的后代）還從來沒吃過肉。我妻子和我在孩子小的時候嚴重依賴豆制品，所以當我第一次知道豆制品可能會帶來的健康問題時嚇了一大跳。我們現在已經擴大了我們的菜單范圍，以便獲得植物蛋白，比如小扁豆、黑豆、豇豆。但仍舊包括一定量的大豆。我們只是檢查食物的成分以避免它們存在我們不知道的危險，并且盡最大可能買有機食物。就像衛(wèi)生領域的其他大多數事情一樣，重點是要適度。Kaayla Daniel也同意這一觀點。她說："醬湯、豆豉、老式豆腐，所有這些豆制品都應該適當食用，這些食品都是滋補食品，并不存在太大的風險。"

    讓它發(fā)酵

    說到大豆和健康，意見總是不統一。但是有一件事似乎是支持方和反對方都同意的，發(fā)酵后的大豆對人身體有好處。

    發(fā)酵工藝會改變大豆的化學組成，從而降低有害異黃酮（植物雌激素）的含量�？茖W研究已經發(fā)現，未發(fā)酵的大豆食品（大豆、大豆粉）含異黃酮的量是發(fā)酵后的3倍之多。

    發(fā)酵型大豆食品包括醬油和大豆醬，這是做醬湯最常用的佐料。這是最常見的與醬湯。素食者們以后將會認可豆豉，這是一種經常用來代替肉類的發(fā)酵豆粕。

    更具冒險精神的人們還可以考慮吃些納豆--有股惡臭味的豆醬。一項研究表明，納豆中的一種酶或許可以有效地對抗阿爾茨海默氏癥。研究人員推論說，研究人員推論說，這種酶可以破壞積存在大腦中的造成記憶改變的蛋白質。