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每天10个果,医生远离你?
Will 10 apples a day keep the doctor away?

2017-4-19 09:13| 发布者: 岁月如歌| 查看: 168| 评论: 0

摘要: I have just eaten a delicious conference pear weighing about 180g. I do not normally weigh snacks, but the recently reported health benefits of eating more fruit and vegetables has inspired me to dig ...
I have just eaten a delicious conference pear weighing about 180g. I do not normally weigh snacks, but the recently reported health benefits of eating more fruit and vegetables has inspired me to dig out the scales.

A study published last month showed that, as expected, people who eat fruit and vegetables regularly cut their risk of dying from several diseases such as stroke, cancer and heart disease. Generally, the higher the intake of fruit and vegetables, the lower the risk.

Here’s the new bit, according to the paper in the International Journal of Epidemiology, the optimum intake was about 800g per day. Since 80g counts as one serving — roughly one small banana or pear, or three heaped tablespoons of cooked veg — this equates to 10 portions. Given that two out of three Britons struggle to hit the recommended target of five a day, the news that we should now be aiming for 10 was greeted with incredulity.

Researchers from Norway, the UK and US pooled data from 95 separate studies, involving a total of about 2m people. Each of those studies had one thing in common: they asked participants about their dietary intake and measured health outcomes, such as rates of cancer, stroke or heart disease.

What works

A meta-analysis of that pooled data suggested that, compared with eating no fruits and vegetables, overall health outcomes improve with every 200g increment, up to 800g (up to 600g for those with cancer). Unsurprisingly, few people manage to eat more than 800g, meaning that scientists are unable to reliably investigate the benefits of higher intakes (which, I assume, accrue mainly to toilet-roll manufacturers).

Even so, modest amounts seem to make a difference. Eating 200g of fresh produce (about two-and-a-half portions) appeared to cut the risk of cardiovascular disease by 13 per cent; the risk of dying from cancer by 4 per cent; and the risk of premature death by 15 per cent.

Upping daily intakes to 800g brings even better news: a 28 per cent reduction in risk of cardiovascular disease; a 13 per cent reduction in total cancer risk; and a 31 per cent cut in the risk of premature death. Dr Dagfinn Aune from Imperial College’s School of Public Health, who led the analysis, estimated that about 7.8m deaths worldwide per year could be prevented if people ate 10 a day.

What to eat?

Some fruits and vegetables seemed especially protective for certain conditions. Those wanting to fend off early death, particularly from stroke or heart disease, could add the following to their plates: apples, pears, citrus fruits, spinach, lettuce, chicory, and cruciferous vegetables such as broccoli, cabbage and cauliflower. For cancer, the researchers suggested a possible benefit from green and yellow vegetables, such as peppers and green beans and, again, cruciferous vegetables.

This study shows a correlation rather than causation. The researchers have not proved that dining on fresh produce fends off death and disease; it could be that people who eat more healthily also exercise more and are less likely to smoke, with these confounding behaviours really responsible for their rude health. The fact, however, that incrementally higher intakes were associated with incrementally lower risks, though, adds weight to the idea that a healthy diet plays a role.

Other research points to mechanisms by which fruits and vegetables work their therapeutic magic. They are known to reduce cholesterol and blood pressure, and to contain antioxidants that help to repair DNA damage. This last factor is thought to have a bearing on cancer risk. Tumours usually begin with rogue cells whose growth can’t be kept in check.

Dr Aune said that, even though further research was needed to pin down the details, “a high intake of fruit and vegetables holds tremendous health benefits, and we should try to increase their intake in our diet”.

Whole plant foods beat processed versions such as smoothies, which can be high in sugar. Nutritional supplements are no substitute; Dr Aune said there was no evidence they cut the risk of disease.

The verdict

Headlines might have suggested otherwise but the new paper, persuasive though it is, did not prompt a change in the official five-a-day message. This is pragmatic: those already managing five are health-conscious and self-motivated enough to raise their cruciferous-munching ambitions without official haranguing. Those who are not yet heeding the message would risk becoming disheartened at the sudden shifting of the nutritional goalposts.

Anyway, back to the scales. With each pear clocking in at nearly 200g, I did fleetingly wonder whether I could tick off my 800g with three more ripe beauties from the fruit bowl, currently sitting atop two wrinkly apples and an unappealing banana. Alas not — the biggest benefits come from eating a variety of fruits and vegetables, with their corresponding panoply of nutrients. My ugly fruit friends: your time has come.

我刚吃了一枚重约180克的梨子,很好吃。我通常不会称零食的重量,但最近看到有关多吃水果和蔬菜有益健康的报道后,我把秤找了出来。

2月发表的一项研究表明,正如预期的那样,经常吃水果和蔬菜,能降低死于中风、癌症和心脏病等几种疾病的风险。一般而言,水果和蔬菜摄入量越高,这种风险就越低。

根据《国际流行病学杂志》(International Journal of Epidemiology)的这篇文章,新的发现是,最优摄入量是每天约800克。由于80克算一份——差不多是一根小香蕉或小个儿梨子,或满满3大汤匙煮熟的蔬菜——800克相当于10份。鉴于三分之二的英国人连每天5份的推荐摄入量都难以达到,每天应该争取吃10份的消息让人觉得匪夷所思。

来自挪威、英国和美国的研究人员汇集了95项独立研究的数据,覆盖约200万研究对象。每项研究都有一个共同点:他们向参与者询问他们的饮食摄入量,并衡量健康结果,比如癌症、中风或心脏病的发病率。

什么管用

对这些汇总数据的荟萃分析表明,与不吃水果和蔬菜相比,摄入量每增加200克,总体健康状况就会有所改善,直至达到800克(对于癌症患者,最高为600克)。不出所料,很少有人的摄入量能超过800克,这意味着科学家们无法可靠地研究更高摄入量的益处(我猜,这主要对卫生卷纸厂商有好处)。

即使如此,适当的摄入量似乎是有作用的。吃200克新鲜农产品(约2.5份),似乎把患上心血管疾病的风险降低13%;把死于癌症的风险降低4%;把早亡风险减低15%。

每天摄入量达到800克会带来更好的消息:心血管疾病风险减少28%;总体癌症风险降低13%;早亡风险降低31%。牵头这项研究的帝国理工学院(Imperial College)公共卫生学院(School of Public Health)的达芬?奥纳(Dagfinn Aune)博士估计,如果每天吃10份水果和蔬菜,那么全世界每年的死亡人数有望减少约780万。

该吃什么?

一些水果和蔬菜似乎对某些疾病尤其具有防范作用。想要防止早亡(特别是中风或心脏病引起的早亡),可以在盘子中添加以下东西:苹果、梨、柑橘类水果、菠菜、莴苣、菊苣以及十字花科蔬菜,比如西兰花、卷心菜和花菜。对于癌症,研究人员提出绿色和黄色蔬菜(如甜椒和四季豆)以及十字花科蔬菜可能有益。

这项研究显示了关联度,而不是因果关系。研究人员还没有证明,食用新鲜农产品可以防范死亡和疾病;可能情况是,那些吃得更健康的人也会锻炼得更多,而且不太可能吸烟——这些组合行为造就了他们的良好健康。然而,递增的摄入量与逐渐降低的风险存在关联的事实,增加了健康饮食起作用的说法的可信度。

其他研究指向了水果和蔬菜发挥其神奇疗效的机制。人们已知道,水果和蔬菜可以降低胆固醇和血压,并含有抗氧化剂,有助于修复受损DNA。DNA受损据信与癌症风险有关。肿瘤通常始于生长失控的“流氓细胞”。

奥纳博士表示,尽管需要进一步的研究来确定细节,但“大量摄入水果和蔬菜对健康有很大的好处,我们应该努力在饮食中增加它们的摄入量”。

天然植物食物胜过冰沙等加工食品。沙冰的含糖量可能很高。营养补充品不能替代蔬菜水果;奥纳博士说,没有证据表明营养补充品会降低患病风险。

结论

新闻标题也许给人留下不同印象,但是这篇新论文虽有说服力,却并未促使官方调整每天5份的推荐摄入量。这是务实的:那些每天已摄入5份的人很重视健康,他们会自我激励,即使没有官方的强力说教,也会提高十字花科蔬菜摄入量的目标。而那些摄入量还不到5份的人,对营养目标的突然上调可能感到沮丧。

无论如何,再说回到秤吧。鉴于每只梨的重量接近200克,有一个念头在我脑海里短暂闪现:我要不要再吃三个美味的熟梨,以便一口气达到800克的单日目标?眼下这些梨就在我面前的果盘里,躺在两个皱巴巴的苹果和一根难看的香蕉上。但是不行——最大的健康效益来自于食用多种水果和蔬菜,吸取它们各自蕴含的营养成分。我的丑陋的水果朋友们:吃掉你们的时间到了。

译者/何黎


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