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青菜不要用燙的！ 英研究：水煮花椰菜抗癌物損失七成
Boiling vegetables like broccoli and cabbage seriously undermines any health benefits derived from eating them, according to new research.
While past studies suggest brassica vegetables - which includes broccoli, cauliflower, cabbage and Brussel sprouts - can reduce the risk of cancer, a new study found that the standard British cooking practice of boiling them removes up to three-quarters of their anti-cancer properties.
Researchers found by boiling, particularly for long periods, compounds known as glucosinalates - which metabolise into cancer preventative isothiocyanates and also help prevent heart disease - were leeched into boiling water.
And Professor Paul Thornalley, who led the research, said it essentially showed Brits had for years been losing up to three quarters of the health benefits from Brassica vegetables,
The study found boiling broccoli for half an hour led to a loss of more than three-quarters of the healthy compounds (77 per cent).
And boiling had the same detrimental effect on the other three vegetables in the Brassica family, with cauliflower losing 75 per cent of cancer-fighting glucosinalates, sprouts losing 58 per cent and green cabbage 65 per cent.
But they found when they tested faster but less popular cooking techniques like steaming, microwaving and stir-frying, there were "no significant losses".
Professor Thornalley, from Warwick University, said the research would come as a particular shock in the UK.
He said: "While we don't boil for quite as long as previous generations, most people boil these vegetables in Britain. And these vegetables are a big part of our staple diets.
"Boiling for around 10 to 15 minutes would lose up to 50 per cent of the anti-cancer properties, while half an hour can lose up to 80 per cent.
"Most extensive research shows that Brassica vegetables are the best way of getting compounds that help lower the risk of cancer and heart disease.
"But this research shows that for years, particularly in the UK, we could have been getting up to three or four times more health benefits from these vegetables.
"Boiling for half an hour essentially means we would have to eat three or four times more of the vegetables to get the same health benefits of just one serving if they are steamed, stir-fried or micro-waved."
He added that British cooking habits needed to change, saying: "At a time when it is particularly hard to get people, particularly children, to eat Brassica vegetables, we need to make sure we are getting as much benefit as possible from a serving. That means not boiling the vegetables.
"The more cosmopolitan our diets become, the more the cooking techniques are changing, and celebrity chefs are particularly keen on stir-frying.
"But micro-waving, using a small amount of water is a good way of keeping the health benefits. And with modern kitchen appliances, people can just as easily steam their vegetables."
He said that the Portuguese habit of using boiling water to make soup can retain the anti-cancer compounds.
He added: "The Mediterranean habit of incorporating rocket salad into the diet is very beneficial too, and any people should take advantage of any way they can get these compounds."
The research also found that freezing and then de-frosting fresh Brassica vegetables causes the loss of glucosinalates, while preparing them by shredding had a similar effect
Copyright © 2006 National News +44(0)207 684 3000
http://www.lse.co.uk/ShowStory.asp?story=BW1637452S&news_headline=boiling_broccoli_undermines_health_benefits
Boiling vegetables like broccoli and cabbage seriously undermines any health benefits derived from eating them, according to new research.
While past studies suggest brassica vegetables - which includes broccoli, cauliflower, cabbage and Brussel sprouts - can reduce the risk of cancer, a new study found that the standard British cooking practice of boiling them removes up to three-quarters of their anti-cancer properties.
Researchers found by boiling, particularly for long periods, compounds known as glucosinalates - which metabolise into cancer preventative isothiocyanates and also help prevent heart disease - were leeched into boiling water.
And Professor Paul Thornalley, who led the research, said it essentially showed Brits had for years been losing up to three quarters of the health benefits from Brassica vegetables,
The study found boiling broccoli for half an hour led to a loss of more than three-quarters of the healthy compounds (77 per cent).
And boiling had the same detrimental effect on the other three vegetables in the Brassica family, with cauliflower losing 75 per cent of cancer-fighting glucosinalates, sprouts losing 58 per cent and green cabbage 65 per cent.
But they found when they tested faster but less popular cooking techniques like steaming, microwaving and stir-frying, there were "no significant losses".
Professor Thornalley, from Warwick University, said the research would come as a particular shock in the UK.
He said: "While we don't boil for quite as long as previous generations, most people boil these vegetables in Britain. And these vegetables are a big part of our staple diets.
"Boiling for around 10 to 15 minutes would lose up to 50 per cent of the anti-cancer properties, while half an hour can lose up to 80 per cent.
"Most extensive research shows that Brassica vegetables are the best way of getting compounds that help lower the risk of cancer and heart disease.
"But this research shows that for years, particularly in the UK, we could have been getting up to three or four times more health benefits from these vegetables.
"Boiling for half an hour essentially means we would have to eat three or four times more of the vegetables to get the same health benefits of just one serving if they are steamed, stir-fried or micro-waved."
He added that British cooking habits needed to change, saying: "At a time when it is particularly hard to get people, particularly children, to eat Brassica vegetables, we need to make sure we are getting as much benefit as possible from a serving. That means not boiling the vegetables.
"The more cosmopolitan our diets become, the more the cooking techniques are changing, and celebrity chefs are particularly keen on stir-frying.
"But micro-waving, using a small amount of water is a good way of keeping the health benefits. And with modern kitchen appliances, people can just as easily steam their vegetables."
He said that the Portuguese habit of using boiling water to make soup can retain the anti-cancer compounds.
He added: "The Mediterranean habit of incorporating rocket salad into the diet is very beneficial too, and any people should take advantage of any way they can get these compounds."
The research also found that freezing and then de-frosting fresh Brassica vegetables causes the loss of glucosinalates, while preparing them by shredding had a similar effect
Copyright © 2006 National News +44(0)207 684 3000
http://www.lse.co.uk/ShowStory.asp?story=BW1637452S&news_headline=boiling_broccoli_undermines_health_benefits
花椰菜具有抗癌作用，但是英國一項研究警告，如果用水煮花椰菜，會把其中的抗癌成分損失達七成，因此研究報告建議，烹煮花椰菜最好用蒸的，用炒的，或者微波，就是別用水煮的。
英國瓦威克大學針對不同烹調方式對花椰菜、青花菜、甘藍菜（高麗菜）等十字花科蕓薹屬蔬菜抗癌效果的影響進行研究，發現這類青菜中的抗癌成分硫配糖體會在水煮過程中流失，青花菜燙5分鐘，硫配糖體損失15%，10分鐘損失40%，30分鐘損失達77%，花椰菜（白色）燙30分鐘損失75%，高麗菜損失65%，包心菜中的這種成分則損失58%。
過去的醫學研究已經證實，這類蔬菜中的硫配糖體會促使人體產生對抗癌症的酵素，有助於防癌和預防心血管疾病。研究負責人醫學博士索納里教授說，「如果你想獲得一天吃五份蔬菜的最大健康效果，就不要用水煮的，應該考慮用蒸的，或者微波。」
研究中使用的蔬菜都是從當地超市購買後30分鐘內送回實驗室測驗，烹調方式包括：水煮、蒸、微波和炒，以水煮的影響最大。研究測試的其他方式，蒸0到20分鐘，微波0到3分鐘，以及炒0到5分鐘，硫配糖體的流失都不明顯。研究人員也測試青菜買回後的儲存方式的影響，結果發現，以一般家用冰箱和室溫環境來說，除非存放超過7天會讓硫配糖體些微流失之外，影響並不多。
但是如果儲存環境非常低溫，例如冷凍在攝氏零下85度，花椰菜在解凍過程中會破壞這類抗癌物質，流失約33%。切菜方式的影響大致上也不多，研究人員只有在把這些菜切得很細時發現有明顯的流失，切後六小時硫配糖體損失約75%。
針對瓦威克大學的這份研究，英國營養學基金會營養學家丹尼指出，水煮青菜也會破壞其他營養成分，如維他命C和葉綠素，這項研究讓人們更了解最好的蔬菜烹調方式，她認為，用蒸和微波是最好的，「如果你要用水煮的，也盡可能縮短水煮的時間，而且不要加鹽，因為其他飲食中已經吃進太多鹽分了。」
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