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女性健康:大豆饮食对身体好不好?

更新时间:2019/10/2 9:42:25 来源:纽约时报中文网 作者:佚名

Is soya bad for women's health?
女性健康:大豆饮食对身体好不好?

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.

大豆为亚洲人传统饮食已有几千年,但出现在西方餐桌上成为一种常见的食品,则只有大约60年的历史。现在,东西方许多超市都有很多大豆食品,如豆奶、大豆汉堡包和其他以大豆代替肉类的素食产品,当然还有形形色色的传统豆制品,如豆腐、豆豉、豆浆、味噌和酱油等等。

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,大豆饮食相比其他食品,还能降低罹患心脏病的风险。大豆可提供蛋白质、不饱和脂肪酸、维生素B、纤维、铁、钙和锌等人体所需营养,是一种可取代肉类的健康食物,因此在西方越来越受欢迎。不过,尽管在过去的十年有越来越多的人认为大豆有益于健康,但也出现了一种新的担忧,即认为大豆可能会干扰人体内的荷尔蒙。

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.

大豆究竟是有害还是有益于健康?之所以出现这种争论,是因为大豆所含的异黄酮特别高。异黄酮这种化合物具有雌激素的性能,意味其作用类似于主要的女性性激素,即雌激素,并且还会与人体内的雌激素受体结合,而雌激素则可能刺激某些类型的乳腺癌细胞的生长。

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.

不过,虽然科学家广泛研究异黄酮对人体的影响已几十年,但到底会否导致癌症风险的升高,至今未能有明确的答案。

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,常吃大豆似乎能预防癌症,而不是增加患癌的风险。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.)

我们先从观察发现说起。亚洲国家女性常吃大豆食品,与较少食用大豆的美国女性相比,其患乳腺癌的风险要低30%。例如,日本的人平均异黄酮摄入量在30至50毫克之间,而欧洲和美国的人均摄入量不足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,摄入大豆也会降低癌症病情。美国麻省塔夫茨大学(Tufts University)教授张芳芳(Fang Fang Zhang)对生活在美国的6000名乳腺癌患者进行了人口调查,发现常吃大豆的女性癌症患者死亡率要低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.

大豆的益处对于激素受体呈阴性的乳腺癌患者中最为显著。这是一种症状较严重的乳腺癌,因为肿瘤缺乏雌激素和孕酮受体,因此做激素治疗效果不好。

“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.

张芳芳说:“我们的研究发现是,激素受体呈阴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,如果大豆对身体健康有益,要确切地一一指出大豆有哪些好处还是很困难的。

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.

大豆常被人们作为一种健康饮食,用来取代红肉。人们认为常食红肉患心脏病和癌症的风险就会比较高。

“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.

美国华府乔治城大学医学院(Georgetown University School of Medicine)的肿瘤学教授李娜‧克拉克(Leena Hilakivi-Clarke)说:“没有人做过这样的研究,先让人吃大豆食品,然后在一段时间观察他们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.

大豆与患乳腺癌的风险这二者间关联性有多大?一项对有关研究做的整合分析将身体质量指数(BMI)这种常见的健康指数计入后发现,二者之间关联性并不强。

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

其结论意味,患乳腺癌风险不高可能是由于BMI数较低,而不是由于经常食用大豆。

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.

要是大豆真的能够降低患乳腺癌的风险,有可能是因为大豆的异黄酮能加速细胞的凋亡。细胞凋亡是一种基因编程机制,当细胞受到无法修复的DNA损伤时,会主动自我毁灭。如果没有这个自我清除,受损的细胞就会生成为癌细胞。

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

既然大豆能降低患乳腺癌的风险,那么大豆致癌一说又从何而来?

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.

因为,在实验室研究中,确实发现大豆可以刺激癌细胞的生长。在2001年的一项实验,研究人员给免疫系统受损和患有癌症的老鼠喂食异黄酮,并用了11周时间测量这些老鼠的肿瘤大小变化,结果发现异黄酮能促进癌细胞生长。研究人员然后改換无异黄酮的饮食喂养这些老鼠,其后9周老鼠的肿瘤竟然逐渐消失。在1999年的另一项研究,研究人员将人类乳腺癌细胞植入老鼠体内,并给一些老鼠喂食异黄酮。他们也发现,老鼠饮食中的异黄酮会促进癌肿瘤的生长。

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结论,2010年对100多项研究的整合分析得出的结论是,在总体上,实验室实验并未显示大豆食品会导致乳腺癌风险的显著增加。

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.

为何无法得出一个确切的答案?其中一个原因是异黄酮在人体内会是两种相反的雌激素反应。我们进食大豆后,大豆中异黄酮如果与人体内的雌激素α受体结合,就会刺激肿瘤的生长速度,但要是与雌激素β受体结合,就会降低生长速度,诱导受损细胞自我凋亡。

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.

马里兰州约翰霍普金斯医学院(Johns Hopkins School of Medicine)的流行病学和肿瘤学教授布鲁斯·特托克(Bruce Trock)表示,异黄酮在人体更倾向于与受体β结合。这使得异黄酮降低癌症风险的可能性更大。

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

或许,大豆对乳腺癌风险的影响是取决于我们从何时开始食用。

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.

特托克说,大多数针对亚洲人群的研究,其研究对象的女性,大豆是从小吃到大,甚至还可能在母亲子宫时已开始接触大豆。而西方研究涉及的女性大多在人生较晚的时候才开始食用大豆。

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

他说:“在动物中龄时候才开始喂食大豆似乎并不能降低患肿瘤的风险或生长速度。”

“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.”

“要是研究人员在老鼠青春期前开始喂食大豆,然后让老鼠接触致癌物质,老鼠即使患生长肿瘤,但其肿瘤也会比没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%.)

同时,明尼苏达大学(University of Minnesota)的营养学教授明迪·库泽尔(Mindy Kurzer)表示,临床和人口数据显示,即使考虑到安慰剂效应,每天食用大豆也能使女性更年期潮热症状的频率和严重程度减轻一半。另一方面,如果女性服用雌激素药物会使潮热减少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.

有些研究发现,大豆有益于健康很大程度上是由女性产生一种细菌马雌酚之能力而决定。约30%至50%的成年人在食用大豆后,其肠道内会产生马雌酚。一项研究发现,给无法自己产生马雌酚的更年期妇女服用马雌酚补充剂可以显著降低潮热的发生率和严重程度症状。

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.

有可能是某人体内产生马雌酚的能力,而不是马雌酚本身,才是大豆有益于更年期女性的原因。例如,一篇论文提出这样的看法,中国人之所以能够更有效地消化和吸收大豆中的营养物质,是因为他们的祖先已经吃了几千年的大豆。

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.

这可以解释如下的一个现象。研究发现,从亚洲国家移民到美国的人到第二代时,尽管患乳腺癌的风险增高,但仍然低于西方人,即或他们已习惯于西餐饮食。

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.

研究还发现,人生早期开始食用大豆也可以降低患心血管疾病的风险。事实上,人口研究提出这样一个看法,认为摄入大豆异黄酮或许是导致亚洲和西方国家心血管疾病发病率有差异的原因。这是因为已发现大豆可以降低血液中有害的低密度脂蛋白胆固醇(LDL)的水平,而低密度脂蛋白胆固醇是引发心脏病的主要原因之一。

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

但这可能并非大豆的功劳,有可能只是因为大豆含量高的饮食中不健康食品的分量较小。

“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.”

维珍尼亚大学(University of Virginia)的妇产科教授乔安‧品克顿(JoAnn Pinkerton)说:“注重健康的人常吃大豆来代替其他高饱和脂肪的食物,如肥肉和全脂乳制品。而多数大豆食品的饱和脂肪含量都很低。”

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.

也有人担心吃大豆会导致前列腺癌。不过,去年的一项研究却发现,经常食用大豆食品相反可以降低患前列腺癌的风险近30%。大豆不会影响男性的睾丸激素水平,原因何在还不清楚,唯一所知的是,大豆多的饮食通常比较健康。

“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、伊利诺伊大学(University of Illinois)组织微环境培训计划的博士前研究员凯萨琳·安普盖特(Catherine Applegate)说:“经过多年的研究,尽管不断出现的新研究可能有自相矛盾之处,但我们仍然坚持目前的结论,即大豆对预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.

大豆对身体的益处也取决于我们所食用的大豆种类。与加工过的大豆食品相比,毛豆等未经加工的大豆所含的异黄酮含量也不相同,而且食品与大豆越接近,其异黄酮含量就越高。毛豆每100克含有大约18毫克的异黄酮,而豆浆的异黄酮含量则在0.7毫克到11毫克之间。

“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.

特托克说:“我们唯一能说的是,食用大豆食品量如果符合亚洲大豆饮食,包括豆腐、发酵大豆食品和豆浆之类,对女性来说应该是安全的。但研究也表明,大豆加工程度越高,异黄酮的含量就越低,而异黄酮就是我们认为能保护我们身体的元素。”

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.

人类对大豆已进行了几十年的大量研究。迄今没有一项研究是完美的,如同其他营养研究一样,研究结果往往只能显示食品和健康是相关的,但无法证明二者之间有因果关系。

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

虽然无法证明因果关系,但所有研究都不约而同地明确指出,以大豆食物为盘中餐是有益于身体健康的。即或对身体有益仅仅是因为取代了不健康的食物,大豆也值得你的青睐。

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