個人健康
雞蛋可能增加患心臟病風險
2013年07月23日
幾周之內，同一批研究者第二次報告：人們吃的食物和腸道內的細菌可能會提高心臟病風險。
兩周前，他們說：基於肉毒鹼——紅肉中的一種物質——對腸道細菌的作用，它會讓人更可能患心臟疾病。這一次，他們又稱：蛋黃中大量存在的卵磷脂亦有同樣效果。
- 檢視大圖
Macida
這項卵磷脂研究發表在4月24日的《新英格蘭醫學雜誌》(New England Journal of Medicine)上；它體現了人們對體內細菌是如何影響健康和疾病的關注正日益增長。長期以來，科學家都關注着飲食習慣在心臟病中的作用；而將視野擴大至細菌則為研究拓開了一片新天地。
「我們腸道中的微生物也許和心臟病有關。」 該項目的第一研究者、克利夫蘭醫學中心勒納研究所(Cleveland Clinic Lerner Research Institute)細胞與分子醫學系主任斯坦利·黑曾(Stanley Hazen)博士說。
我們吃掉雞蛋後，一系列的事件自身體消化卵磷脂開始。卵磷脂被降解為其組成部分，包括一種叫做膽鹼的化學物質。腸道內細菌代謝膽鹼，釋放出一種可被肝臟轉化成氧化三甲胺(TMAO)的物質。血液中高水平的氧化三甲胺是與心肌梗塞和腦卒中有關聯的。
為證明雞蛋能影響氧化三甲胺水平，黑曾博士讓志願者吃掉兩隻煮熟的雞蛋——他們血液中的氧化三甲胺隨即增高。但如果志願者事先服用抗生素，清除了腸道內細菌，再吃雞蛋就不產生類似效果了。
為觀察氧化三甲胺與心血管疾病的關係，研究者研究了4000名曾在克利夫蘭醫學中心看過病的病人：血液中氧化三甲胺越多的人，越有可能在隨後3年患心肌梗塞或腦卒中。
黑曾博士說，紅肉中的肉毒鹼與卵磷脂在化學上類似。就像卵磷脂一樣，肉毒鹼被消化後，膽鹼釋放出來，然後被腸道細菌利用。
不過，新研究並沒有直接證明降低氧化三甲胺能阻止心臟病的發生。這需要大範圍地研究體內氧化三甲胺水平降低的人群，應該可以在素食者和有高纖維飲食習慣的人群中展開。
黑曾說，擔心自己患心肌梗塞的人可以考慮在飲食中減少卵磷脂和膽鹼的量，也就是少吃高脂肪和高膽固醇食物；也應該盡量不要吃添加膽鹼的營養補充劑或維生素。
在一篇相關社論中，波士頓布萊根婦女醫院(Brigham
and Women』s Hospital)的約瑟夫·洛斯卡爾佐(Joseph
Loscalzo)醫生認為，以後也許有其他降低血中氧化三甲胺水平的辦法。比如讓人們服用益生菌，促進不會導致氧化三甲胺水平提高的細菌增長；或服用抑
制合成氧化三甲胺的藥物。不過，這類益生菌和藥物尚不存在——即便是那群特別能提高氧化三甲胺的細菌也還沒被甄別出來呢。
本文最初發表於2013年4月25日。翻譯：孫舒雯
心臟病，吃出來
報道 2013年04月19日
近幾十年來，有件事已經獲得大家的普遍共識：食用常見於肉類和黃油中的飽和脂肪，對人體
健康有害。從20世紀60年代開始，就有研究言之鑿鑿地表明，飽和脂肪會升高膽固醇水平，尤其是低密度脂蛋白或稱LDL（也就是所謂“壞膽固醇”），從而
增加心臟病的發病。研究同樣表明，食用多不飽和脂肪——紅花油、玉米油和大豆油——能降低總膽固醇和LDL水平，值得鼓勵。
但是新的研究也許能推翻這種假設。美國國立衛生研究院(National Institutes of Health)等組織的研究人員最近重新審視了1966到1973年間進行的一項被長期忽視的澳大利亞研究。研究中一組心臟病患者飲食中15%的熱量來自 富含Ω-6多不飽和脂肪的食物，而飽和脂肪減少到10%以下。另一組心臟病患者則繼續照常飲食。
平均隨訪時間為39個月，吃富含多不飽和脂肪飲食的患者，膽固醇水平平均降低了13%。但是與保持日常飲食、食物中包括了約15%飽和脂肪的那組相比，他們的死亡風險更大，因心肌梗死而病故的風險尤其顯著。
這一研究結果在當時並未得到充分分析，因為那會兒正好是對多不飽和脂肪油類研究熱情高漲的早期時代——現在卻為一組小型而令人不安的數據增加了分量：食用多不飽和（脂肪）油類，雖然它們毫無疑問能降低膽固醇，但也許仍會增加你的心臟病風險。
更寬泛地來說，新的分析使得原本已不甚明朗的飲食如何影響心臟病風險和整體健康的問題雪上加霜。菲利普·C·卡爾德(Philip C. Calder)是英國南安普敦大學(University of Southampton)的營養免疫學教授，為新分析寫了一篇編者按，他說多不飽和脂肪油類在降低膽固醇的同時，可能也促進了體內的炎性反應，這種炎性反 應可能啟動心臟病，並抵銷油脂“任何可能的健康效應”。
更基本的是，我們尚未完全了解高膽固醇水平在心臟病中究竟扮演了一個怎樣的角色。卡爾德在電子郵件中說到，有些人也許會認為“膽固醇和心臟病之間的 關係實際上沒有我們以為的那麼緊密”。這種可能性雖然令人吃驚，但也印證了另外一些研究，這些研究表明嚴格堅持富含魚油——另一種有益心臟的脂肪——的飲 食，並未有效保護人們免受心肌梗死或中風的風險；而稍微超重的人，甚至達到輕度肥胖的程度，也可能比那些瘦子活得長。
以上種種並不是要說明飲食和心臟病或長壽之間毫無關係。我們知道人工合成的反式脂肪似乎特別危險。而你的飲食與你特定基因之間的關係至關重要。但事 實上，目前來說，我們並不真正知道它是如何起效的。卡爾德說新的分析可能促進人們建議減少植物油的使用，用動物油取而代之，但他目前還不確定是否應得出這 個結論。
但是新的研究也許能推翻這種假設。美國國立衛生研究院(National Institutes of Health)等組織的研究人員最近重新審視了1966到1973年間進行的一項被長期忽視的澳大利亞研究。研究中一組心臟病患者飲食中15%的熱量來自 富含Ω-6多不飽和脂肪的食物，而飽和脂肪減少到10%以下。另一組心臟病患者則繼續照常飲食。
這一研究結果在當時並未得到充分分析，因為那會兒正好是對多不飽和脂肪油類研究熱情高漲的早期時代——現在卻為一組小型而令人不安的數據增加了分量：食用多不飽和（脂肪）油類，雖然它們毫無疑問能降低膽固醇，但也許仍會增加你的心臟病風險。
更寬泛地來說，新的分析使得原本已不甚明朗的飲食如何影響心臟病風險和整體健康的問題雪上加霜。菲利普·C·卡爾德(Philip C. Calder)是英國南安普敦大學(University of Southampton)的營養免疫學教授，為新分析寫了一篇編者按，他說多不飽和脂肪油類在降低膽固醇的同時，可能也促進了體內的炎性反應，這種炎性反 應可能啟動心臟病，並抵銷油脂“任何可能的健康效應”。
更基本的是，我們尚未完全了解高膽固醇水平在心臟病中究竟扮演了一個怎樣的角色。卡爾德在電子郵件中說到，有些人也許會認為“膽固醇和心臟病之間的 關係實際上沒有我們以為的那麼緊密”。這種可能性雖然令人吃驚，但也印證了另外一些研究，這些研究表明嚴格堅持富含魚油——另一種有益心臟的脂肪——的飲 食，並未有效保護人們免受心肌梗死或中風的風險；而稍微超重的人，甚至達到輕度肥胖的程度，也可能比那些瘦子活得長。
以上種種並不是要說明飲食和心臟病或長壽之間毫無關係。我們知道人工合成的反式脂肪似乎特別危險。而你的飲食與你特定基因之間的關係至關重要。但事 實上，目前來說，我們並不真正知道它是如何起效的。卡爾德說新的分析可能促進人們建議減少植物油的使用，用動物油取而代之，但他目前還不確定是否應得出這 個結論。
Eat Your Heart Out
April 19, 2013
Over the last several decades, it has become accepted wisdom that
consuming saturated fat, the type found in meat and butter, is bad for
you. Starting in the 1960s, studies showed convincingly that saturated
fat raises cholesterol levels and that these elevated levels, especially
of low-density lipoprotein cholesterol, or LDL (the so-called bad
cholesterol), increase heart disease. Studies also showed that consuming
polyunsaturated fats — safflower, corn and soybean oils — reduced
people’s levels of overall cholesterol and LDL and should be encouraged.
But new studies may be upending those assumptions. Researchers with the National Institutes of Health and other organizations recently resurrected the results of a long-overlooked Australian study conducted from 1966 to 1973, in which one group of men with heart disease increased omega-6-rich polyunsaturated fat intake to 15 percent of calories, while reducing saturated fat intake to less than 10 percent. Another group of men with heart disease continued their normal diets.
The men were followed for an average of 39 months, and those on the polyunsaturated-rich diet lowered their cholesterol levels by an average of 13 percent. But they also were more likely to die, and in particular to die of a heart attack, than those who stuck with their usual diet, which consisted of about 15 percent saturated fat.
This study — the results of which weren’t fully analyzed when it was conducted in the early days of enthusiasm for polyunsaturated oils — adds to a small but unsettling body of data suggesting that consuming polyunsaturated oils, even though they reliably lower cholesterol, may nevertheless increase your risk of heart disease.
In broader terms, the new analysis muddies the already murky issue of just how diet affects heart-disease risk and health in general. Polyunsaturated oils, while decreasing cholesterol, may simultaneously promote inflammation throughout the body, says Philip C. Calder, a professor of nutritional immunology at the University of Southampton, in England, who wrote an editorial accompanying the new analysis. This inflammation may initiate heart disease and “outweigh any possible good effect” of the oils.
More fundamentally, we don’t fully understand how high cholesterol levels contribute to heart disease. Some would argue, Calder wrote in an e-mail, that “the link between cholesterol and heart disease is not actually as strong as we think.” That possibility, while startling, lends credence to other studies showing that assiduously sticking to a diet rich in fish oils, another heart-healthful fat, doesn’t necessarily protect people from heart attacks or strokes; and that those who carry extra pounds, even to the point of being slightly obese, may live longer than people who weigh less.
None of this is to say that there are no links between diet and heart disease or longevity. We know that synthetic trans fats seem particularly risky. And that the interplay between what you eat and your particular genetics may be primary. But the truth is, at this point, we don’t truly understand how it all works. Calder said the new analysis might prompt some people to recommend lowering the use of vegetable oils, substituting animal fats instead, but that he wasn’t ready to come to that conclusion.
But new studies may be upending those assumptions. Researchers with the National Institutes of Health and other organizations recently resurrected the results of a long-overlooked Australian study conducted from 1966 to 1973, in which one group of men with heart disease increased omega-6-rich polyunsaturated fat intake to 15 percent of calories, while reducing saturated fat intake to less than 10 percent. Another group of men with heart disease continued their normal diets.
The men were followed for an average of 39 months, and those on the polyunsaturated-rich diet lowered their cholesterol levels by an average of 13 percent. But they also were more likely to die, and in particular to die of a heart attack, than those who stuck with their usual diet, which consisted of about 15 percent saturated fat.
This study — the results of which weren’t fully analyzed when it was conducted in the early days of enthusiasm for polyunsaturated oils — adds to a small but unsettling body of data suggesting that consuming polyunsaturated oils, even though they reliably lower cholesterol, may nevertheless increase your risk of heart disease.
In broader terms, the new analysis muddies the already murky issue of just how diet affects heart-disease risk and health in general. Polyunsaturated oils, while decreasing cholesterol, may simultaneously promote inflammation throughout the body, says Philip C. Calder, a professor of nutritional immunology at the University of Southampton, in England, who wrote an editorial accompanying the new analysis. This inflammation may initiate heart disease and “outweigh any possible good effect” of the oils.
More fundamentally, we don’t fully understand how high cholesterol levels contribute to heart disease. Some would argue, Calder wrote in an e-mail, that “the link between cholesterol and heart disease is not actually as strong as we think.” That possibility, while startling, lends credence to other studies showing that assiduously sticking to a diet rich in fish oils, another heart-healthful fat, doesn’t necessarily protect people from heart attacks or strokes; and that those who carry extra pounds, even to the point of being slightly obese, may live longer than people who weigh less.
None of this is to say that there are no links between diet and heart disease or longevity. We know that synthetic trans fats seem particularly risky. And that the interplay between what you eat and your particular genetics may be primary. But the truth is, at this point, we don’t truly understand how it all works. Calder said the new analysis might prompt some people to recommend lowering the use of vegetable oils, substituting animal fats instead, but that he wasn’t ready to come to that conclusion.
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