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女性健康:大豆飲食對身體好不好?

更新時間:2019/10/2 9:42:25 來源:紐約時報中文網 作者:佚名

Is soya bad for women's health?
女性健康:大豆飲食對身體好不好?

Consumed in many traditional Asian populations for millennia, soya has only been a common part of the Western diet for around 60 years. Now, many of our supermarkets are full of soy milk alternatives, soy burgers and other soya-based meat replacements – not to mention traditional soy-based products like tofu, tempeh, soya milk, miso and soya sauce.

大豆為亞洲人傳統飲食已有幾千年,但出現在西方餐桌上成為一種常見的食品,則只有大約60年的歷史。現在,東西方許多超市都有很多大豆食品,如豆奶、大豆漢堡包和其他以大豆代替肉類的素食產品,當然還有形形色色的傳統豆制品,如豆腐、豆豉、豆漿、味噌和醬油等等。

In the meantime, soya has been linked to a lower risk of heart disease compared to other diets. As a good source of protein, unsaturated fatty acids, B vitamins, fibre, iron, calcium and zinc, it is becoming increasingly popular in the West as a healthy substitute for meat. But despite more people associating soya with health over the last decade, one fear has come to the fore: the idea that soya can disrupt our hormones.

除了是美味食品,大豆飲食相比其他食品,還能降低罹患心臟病的風險。大豆可提供蛋白質、不飽和脂肪酸、維生素B、纖維、鐵、鈣和鋅等人體所需營養,是一種可取代肉類的健康食物,因此在西方越來越受歡迎。不過,盡管在過去的十年有越來越多的人認為大豆有益于健康,但也出現了一種新的擔憂,即認為大豆可能會干擾人體內的荷爾蒙。

The controversy around soya comes down to its uniquely high content of isoflavones. These compounds have oestrogenic properties, which means they act like oestrogen, the primary female sex hormone, and bind to oestrogen receptors in the body – and oestrogen can fuel the growth of some types of breast cancer.

大豆究竟是有害還是有益于健康?之所以出現這種爭論,是因為大豆所含的異黃酮特別高。異黃酮這種化合物具有雌激素的性能,意味其作用類似于主要的女性性激素,即雌激素,并且還會與人體內的雌激素受體結合,而雌激素則可能刺激某些類型的乳腺癌細胞的生長。

But while scientists have extensively researched the compound’s effects in the body over the last few decades, the answer about whether isoflavones themselves can contribute to cancer risk isn’t straightforward.

不過,雖然科學家廣泛研究異黃酮對人體的影響已幾十年,但到底會否導致癌癥風險的升高,至今未能有明確的答案。

And often, it seems soya protects against cancer risk – rather than making it worse. But exactly why that is isn’t certain.

通常而言,常吃大豆似乎能預防癌癥,而不是增加患癌的風險。但究其原因,尚不清楚。

To start, there are the observational findings. High soya intake among women in Asian countries has been linked to their 30% lower risk of developing breast cancer compared to US women, who eat much less soya. (The average person’s intake of isoflavones in Japan, for example, is between 30 and 50mg, compared to less than 3mg in Europe and the US.)

我們先從觀察發現說起。亞洲國家女性常吃大豆食品,與較少食用大豆的美國女性相比,其患乳腺癌的風險要低30%。例如,日本的人平均異黃酮攝入量在30至50毫克之間,而歐洲和美國的人均攝入量不足3毫克。

Soya also has been correlated with reducing breast cancer’s severity. Fang Fang Zhang, associate professor at Tufts University in Massachusetts, carried out population research among 6,000 women with breast cancer living in the US and found a 21% reduction in mortality among those who consumed more soya.

即或患上乳腺癌,攝入大豆也會降低癌癥病情。美國麻省塔夫茨大學(Tufts University)教授張芳芳(Fang Fang Zhang)對生活在美國的6000名乳腺癌患者進行了人口調查,發現常吃大豆的女性癌癥患者死亡率要低21%。

Its benefits were strongest in women with hormone-receptor-negative breast cancer, a more aggressive type of breast cancer where tumours lack oestrogen and progesterone receptors, and therefore doesn’t respond well to hormone therapies.

大豆的益處對于激素受體呈陰性的乳腺癌患者中最為顯著。這是一種癥狀較嚴重的乳腺癌,因為腫瘤缺乏雌激素和孕酮受體,因此做激素治療效果不好。

“Our findings suggest that, for women with hormone-receptor-negative breast cancer, soya food consumption may potentially have a beneficial effect to improve survival,” Zhang says.

張芳芳說:“我們的研究發現是,激素受體呈陰性的乳腺癌患者食用大豆食品可能有助于提高生存率。”

Not soy easy

搞清大豆不容易

Even so, it’s difficult to conclusively isolate soya’s benefits – if there are any.

即便如此,如果大豆對身體健康有益,要確切地一一指出大豆有哪些好處還是很困難的。

Soya is often consumed as part of a healthy diet and as a substitute for red meat, which is associated with a higher risk of heart disease and cancer.

大豆常被人們作為一種健康飲食,用來取代紅肉。人們認為常食紅肉患心臟病和癌癥的風險就會比較高。

“No one has given people soya foods, then looked at whether they’re more or less likely to get breast cancer over time than those not given soya,” says Leena Hilakivi-Clarke, professor of oncology at Georgetown University School of Medicine in Washington DC.

美國華府喬治城大學醫學院(Georgetown University School of Medicine)的腫瘤學教授李娜‧克拉克(Leena Hilakivi-Clarke)說:“沒有人做過這樣的研究,先讓人吃大豆食品,然后在一段時間觀察他們是否比那些不吃大豆的人更容易或更不容易患上乳腺癌。”

One review of evidence into soya’s effect on breast cancer risk found that studies that adjusted for body mass index (BMI), a common marker of health, showed a weaker association for soya than those that didn’t.

大豆與患乳腺癌的風險這二者間關聯性有多大?一項對有關研究做的整合分析將身體質量指數(BMI)這種常見的健康指數計入后發現,二者之間關聯性并不強。

This means a reduced risk of breast cancer could have been due to lower BMI, not to soya consumption.

其結論意味,患乳腺癌風險不高可能是由于BMI數較低,而不是由于經常食用大豆。

If soya does lower breast cancer risk, it may be because its isoflavones can enhance apoptosis: a genetically programmed mechanism that tells cells to self-destruct when they get DNA damage they’re not able to repair. Without this process, damaged cells can form into cancer.

要是大豆真的能夠降低患乳腺癌的風險,有可能是因為大豆的異黃酮能加速細胞的凋亡。細胞凋亡是一種基因編程機制,當細胞受到無法修復的DNA損傷時,會主動自我毀滅。如果沒有這個自我清除,受損的細胞就會生成為癌細胞。

So where did the concern that soya causes cancer come from?

既然大豆能降低患乳腺癌的風險,那么大豆致癌一說又從何而來?

It’s true that soya has been found to fuel the growth cancer cells in lab research. In one experiment from 2001, mice with inhibited immune systems and with cancerous tumours were fed isoflavones. Their tumours were measured for 11 weeks. The researchers found that the isoflavones resulted in increased cell growth. The mice were then switched to an isoflavone-free diet – and their tumours regressed over the following nine weeks. Meanwhile, in a study from 1999, researchers implanted human breast cancer cells into mice, and some were fed isoflavones. They also found that dietary isoflavones enhance the growth of cancerous tumours.

因為,在實驗室研究中,確實發現大豆可以刺激癌細胞的生長。在2001年的一項實驗,研究人員給免疫系統受損和患有癌癥的老鼠喂食異黃酮,并用了11周時間測量這些老鼠的腫瘤大小變化,結果發現異黃酮能促進癌細胞生長。研究人員然后改換無異黃酮的飲食喂養這些老鼠,其后9周老鼠的腫瘤竟然逐漸消失。在1999年的另一項研究,研究人員將人類乳腺癌細胞植入老鼠體內,并給一些老鼠喂食異黃酮。他們也發現,老鼠飲食中的異黃酮會促進癌腫瘤的生長。

But a more recent, 2010 review of more than 100 studies concluded that, overall, lab experiments have shown no significant increased risk of breast cancer.

但最新的研究又有不同的結論,2010年對100多項研究的整合分析得出的結論是,在總體上,實驗室實驗并未顯示大豆食品會導致乳腺癌風險的顯著增加。

One reason there isn’t a more definitive answer is because isoflavone either acts like oestrogen in the body, or its opposite. When we eat soya, isoflavone either binds to the alpha oestrogen receptor in the body, which stimulates a tumour’s growth rate, or the beta receptor, which decreases growth rate and induces apoptosis.

為何無法得出一個確切的答案?其中一個原因是異黃酮在人體內會是兩種相反的雌激素反應。我們進食大豆后,大豆中異黃酮如果與人體內的雌激素α受體結合,就會刺激腫瘤的生長速度,但要是與雌激素β受體結合,就會降低生長速度,誘導受損細胞自我凋亡。

Isoflavone prefers to bind to beta receptors, says Bruce Trock, professor of epidemiology and oncology at Johns Hopkins School of Medicine in Maryland in the US. That makes it more likely to reduce potential cancer risk.

馬里蘭州約翰霍普金斯醫學院(Johns Hopkins School of Medicine)的流行病學和腫瘤學教授布魯斯·特托克(Bruce Trock)表示,異黃酮在人體更傾向于與受體β結合。這使得異黃酮降低癌癥風險的可能性更大。

The impact of soya on breast cancer risk may depend on when we start eating it.

或許,大豆對乳腺癌風險的影響是取決于我們從何時開始食用。

Most studies on Asian populations included women who have eaten it since early childhood and were probably also exposed to it in the uterus, says Trock, compared to Western studies involving women who mostly didn’t eat soya until later in life.

特托克說,大多數針對亞洲人群的研究,其研究對象的女性,大豆是從小吃到大,甚至還可能在母親子宮時已開始接觸大豆。而西方研究涉及的女性大多在人生較晚的時候才開始食用大豆。

“Giving soya to animals at the equivalent of middle age doesn’t seem to reduce risk or growth rate of tumours,” he says.

他說:“在動物中齡時候才開始喂食大豆似乎并不能降低患腫瘤的風險或生長速度。”

“But if researchers feed mice [soy] prior to puberty, then expose them to carcinogens, they get fewer and smaller tumours than if you don’t give them soya.”

“要是研究人員在老鼠青春期前開始喂食大豆,然后讓老鼠接觸致癌物質,老鼠即使患生長腫瘤,但其腫瘤也會比沒有喂食大豆的老鼠更少一些和小一些。”

Soya cycle

大豆周期

Meanwhile, clinical and population data shows daily soya intake can halve the frequency and severity of hot flashes even when the placebo affect is taken into consideration, says Mindy Kurzer, professor of nutrition at the University of Minnesota. (Taking oestrogen medication, on the other hand, brings hot flushes down by 75%.)

同時,明尼蘇達大學(University of Minnesota)的營養學教授明迪·庫澤爾(Mindy Kurzer)表示,臨床和人口數據顯示,即使考慮到安慰劑效應,每天食用大豆也能使女性更年期潮熱癥狀的頻率和嚴重程度減輕一半。另一方面,如果女性服用雌激素藥物會使潮熱減少75%。

Some research has found that these benefits are largely determined by a woman’s ability to produce equol, a bacteria that around 30 to 50 percent of adults produce in their intestines after eating soy. One study found that giving equol supplements to menopausal women who don’t produce it themselves significantly lowered the incidence and severity of hot flushes.

有些研究發現,大豆有益于健康很大程度上是由女性產生一種細菌馬雌酚之能力而決定。約30%至50%的成年人在食用大豆后,其腸道內會產生馬雌酚。一項研究發現,給無法自己產生馬雌酚的更年期婦女服用馬雌酚補充劑可以顯著降低潮熱的發生率和嚴重程度癥狀。

It could be that a person’s ability to produce equol, rather than the equol itself, is responsible for the benefits of soya. One paper argues that Chinese populations, for example, may be better able to digest and extract nutrients from soya because their ancestors have been eating it for thousands of years.

有可能是某人體內產生馬雌酚的能力,而不是馬雌酚本身,才是大豆有益于更年期女性的原因。例如,一篇論文提出這樣的看法,中國人之所以能夠更有效地消化和吸收大豆中的營養物質,是因為他們的祖先已經吃了幾千年的大豆。

This could explain why research has found that, while people who move from Asian countries to the US have an increased risk of breast cancer by the second generation, their risk remains lower than Westerners even when they adopt a Western diet.

這可以解釋如下的一個現象。研究發現,從亞洲國家移民到美國的人到第二代時,盡管患乳腺癌的風險增高,但仍然低于西方人,即或他們已習慣于西餐飲食。

Early soya intake has also been found to reduce the risk of cardiovascular disease. In fact, population studies suggest isoflavone intake could be responsible for the different rates of cardiovascular disease between Asian and Western countries. This is because soya has been found to reduce levels of harmful low-density lipoprotein (LDL) cholesterol in the blood, which is a risk for heart disease.

研究還發現,人生早期開始食用大豆也可以降低患心血管疾病的風險。事實上,人口研究提出這樣一個看法,認為攝入大豆異黃酮或許是導致亞洲和西方國家心血管疾病發病率有差異的原因。這是因為已發現大豆可以降低血液中有害的低密度脂蛋白膽固醇(LDL)的水平,而低密度脂蛋白膽固醇是引發心臟病的主要原因之一。

But may have nothing to do with soya, per se – it could simply be because diets higher in soya are lower in unhealthier foods.

但這可能并非大豆的功勞,有可能只是因為大豆含量高的飲食中不健康食品的分量較小。

“Soya foods are normally eaten in place of other higher saturated fat foods, such as fatty meat and full-fat dairy products,” says JoAnn Pinkerton, professor of obstetrics and gynaecology at the University of Virginia Health System. “Whereas most soya foods are naturally low in saturated fat.”

維珍尼亞大學(University of Virginia)的婦產科教授喬安‧品克頓(JoAnn Pinkerton)說:“注重健康的人常吃大豆來代替其他高飽和脂肪的食物,如肥肉和全脂乳制品。而多數大豆食品的飽和脂肪含量都很低。”

There are also concerns soya could be linked to prostate cancer. However, a review of evidence last year found that regular soya food intake was associated with an almost 30% reduction in risk of developing prostate cancer. Soya doesn’t affect testosterone levels in men, so how this happens isn’t yet known – except that a diet containing more soya is often healthier overall.

也有人擔心吃大豆會導致前列腺癌。不過,去年的一項研究卻發現,經常食用大豆食品相反可以降低患前列腺癌的風險近30%。大豆不會影響男性的睪丸激素水平,原因何在還不清楚,唯一所知的是,大豆多的飲食通常比較健康。

“Throughout the years and despite the constant emergence of new research that could contain potentially conflicting results, we maintain the current conclusion that soya is beneficial in preventing prostate cancer,” says the study’s author Catherine Applegate, a predoctoral fellow from  the University of Illinois's Tissue Microenvironment Training Program.

上述研究的作者、伊利諾伊大學(University of Illinois)組織微環境培訓計劃的博士前研究員凱薩琳·安普蓋特(Catherine Applegate)說:“經過多年的研究,盡管不斷出現的新研究可能有自相矛盾之處,但我們仍然堅持目前的結論,即大豆對預防前列腺癌是有益的。”

Soya’s benefits also depend on the type we consume. Isoflavone content varies in unprocessed soybeans, such as edamame beans, compared to processed soya foods – and the closer the food is to the soyabean, the higher its isoflavone levels. Edamame has around 18mg of isoflavones per 100g, while soya milk has between 0.7 and 11mg.

大豆對身體的益處也取決于我們所食用的大豆種類。與加工過的大豆食品相比,毛豆等未經加工的大豆所含的異黃酮含量也不相同,而且食品與大豆越接近,其異黃酮含量就越高。毛豆每100克含有大約18毫克的異黃酮,而豆漿的異黃酮含量則在0.7毫克到11毫克之間。

“The only thing we can say is that women should be safe to consume soya foods in amounts consistent with Asian diet, including tofu, fermented soya foods and soymilk, but studies shown that the more soya is processed, the lower the level of isoflavones, which we think are protective elements,” says Trock.

特托克說:“我們唯一能說的是,食用大豆食品量如果符合亞洲大豆飲食,包括豆腐、發酵大豆食品和豆漿之類,對女性來說應該是安全的。但研究也表明,大豆加工程度越高,異黃酮的含量就越低,而異黃酮就是我們認為能保護我們身體的元素。”

Soya has been extensively researched over the last few decades. No single study has been perfect, and as with other nutritional research, findings often show correlation – they don’t prove causation.

人類對大豆已進行了幾十年的大量研究。迄今沒有一項研究是完美的,如同其他營養研究一樣,研究結果往往只能顯示食品和健康是相關的,但無法證明二者之間有因果關系。

Even so, the consensus clearly indicates health benefits from eating soya – even if that’s simply because it replaces unhealthier foods.

雖然無法證明因果關系,但所有研究都不約而同地明確指出,以大豆食物為盤中餐是有益于身體健康的。即或對身體有益僅僅是因為取代了不健康的食物,大豆也值得你的青睞。

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