健康飲食結構 低澱粉高脂肪大綱

People who avoid carbohydrates and eat more fat, even saturated fat, lose more body fat and have fewer cardiovascular risks than people who follow the low-fat diet that health authorities have favored for decades, a major new study shows.

一項重大的新研究顯示，比起那些遵循衛生部門數十年來一直推崇的低脂飲食的人，不吃碳水化合物但攝入較多脂肪、乃至飽和脂肪的人，消耗的體脂更多，並且罹患心血管疾病的風險更低。

The findings are unlikely to be the final salvo in what has been a long and often contentious debate about what foods are best to eat for weight loss and overall health. The notion that dietary fat is harmful, particularly saturated fat, arose decades ago from comparisons of disease rates among large national populations.

長期以來，關於哪種食物對減重和身體健康最有好處一直存在爭議，上述結論不太可能成爲定論。幾十年前，通過比較全國大量人口的患病率，人們形成了膳食脂肪、尤其是飽和脂肪對人體有害的概念。

But more recent clinical studies in which individuals and their diets were assessed over time have produced a more complex picture. Some have provided strong evidence that people can sharply reduce their heart disease risk by eating fewer carbohydrates and more dietary fat, with the exception of trans fats. The new findings suggest that this strategy more effectively reduces body fat and also lowers overall weight.

但是，通過在一段時間內評估個人及其飲食習慣，近期的臨牀研究描繪出了一幅更爲複雜的畫面。有些研究提供了非常有力的證據顯示，人們可以通過攝入較少的碳水化合物和較多的膳食脂肪——反式脂肪除外——來大幅度降低罹患心臟疾病的風險。這些新的發現說明，這種做法能更有效地減少體脂，並同時減輕體重。

The new study was financed by the National Institutes of Health and published in the Annals of Internal Medicine. It included a racially diverse group of 150 men and women — a rarity in clinical nutrition studies — who were assigned to follow diets for one year that limited either the amount of carbs or fat that they could eat, but not overall calories.

這項新研究由美國國立衛生研究院(National Institutes of Health)出資，成果發表在了《內科學年鑑》(Annals of Internal Medicine)上。調查對象包括各個族裔的150名男女——這在臨牀營養研究中並不多見。按照指派的結果，這些人必須在一年內遵守限制碳水化合物或脂肪攝入量的飲食要求，但無需限制總體的卡路里攝入量。

“To my knowledge, this is one of the first long-term trials that’s given these diets without calorie restrictions,” said Dariush Mozaffarian, the dean of the Friedman School of Nutrition Science and Policy at Tufts University, who was not involved in the new study. “It shows that in a free-living setting, cutting your carbs helps you lose weight without focusing on calories. And that’s really important because someone can change what they eat more easily than trying to cut down on their calories.”

“據我所知，這屬於首批不限制卡路里攝入的飲食方式長期試驗，”塔夫茨大學弗裏德曼營養科學與政策學院(Friedman School of Nutrition Science and Policy at Tufts University)院長達柳什·莫扎法裏安(Dariush Mozaffarian)說。他沒有參與這項新研究。“這表明，在可以想吃什麼就吃什麼的情況下，減少碳水化合物的攝入有助於減輕體重，而且還不需要關注卡路里。這一點很重要，因爲與努力減少卡路里攝入相比，人們更容易改變飲食的種類。”

Diets low in carbohydrates and higher in fat and protein have been commonly used for weight loss since Dr. Robert Atkins popularized the approach in the 1970s. Among the longstanding criticisms is that these diets cause people to lose weight in the form of water instead of body fat, and that cholesterol and other heart disease risk factors climb because dieters invariably raise their intake of saturated fat by eating more meat and dairy.

自20世紀70年代，羅伯特·阿特金斯博士(Robert Atkins)開始推行低碳水化合物高脂高蛋白飲食以來，此類減肥方式就開始被廣泛採用。一直有批評聲認爲，這種飲食習慣減去的是人體的水份，而不是脂肪，而且膽固醇等心臟疾病的風險因素也會隨之攀升，因爲人們食用了更多的肉類和奶製品，必然會增加飽和脂肪的攝入量。

Many nutritionists and health authorities have “actively advised against” low-carbohydrate diets, said the lead author of the new study, Dr. Lydia A. Bazzano of the Tulane University School of Public Health and Tropical Medicine. “It’s been thought that your saturated fat is, of course, going to increase, and then your cholesterol is going to go up,” she said. “And then bad things will happen in general.”

上述新研究論文的第一作者、杜蘭大學公共衛生及熱帶疾病學院(Tulane University School of Public Health and Tropical Medicine)的莉迪婭·A·巴扎諾博士(Lydia A. Bazzano)表示，許多營養學專家和衛生部門都“大力反對”低碳水化合物的飲食方式。“他們總是認爲，你的飽和脂肪攝入量肯定會增加，然後你的膽固醇就會升高，”她說。“接下來，通常會帶來不良後果。”

The new study showed that was not the case.

這項新研究表明，事實並非如此。

By the end of the yearlong trial, people in the low-carbohydrate group had lost about eight pounds more on average than those in the low-fat group. They had significantly greater reductions in body fat than the low-fat group, and improvements in lean muscle mass — even though neither group changed their levels of physical activity.

在爲期一年的試驗結束時，低碳水化合物攝入小組的成員體重，比低脂肪小組平均多減了8磅左右（約合3.6公斤）。與後者相比，他們的體脂減少量明顯更大，而且精瘦肌肉量也增加了——雖然兩組受試人員均沒有改變身體活動量。

While the low-fat group did lose weight, they appeared to lose more muscle than fat.

儘管低脂肪攝入小組的成員的確減輕了體重，但他們失去的肌肉似乎比脂肪更多。

“They actually lost lean muscle mass, which is a bad thing,” Dr. Mozaffarian said. “Your balance of lean mass versus fat mass is much more important than weight. And that’s a very important finding that shows why the low-carb, high-fat group did so metabolically well.”

“他們減去的其實是精瘦肌肉，這並不好，”莫扎法裏安說。“肌肉量與脂肪量的平衡要比體重本身重要得多。這是一個非常重要的發現，說明了爲什麼低碳水化合物、高脂肪攝入的小組在代謝方面會表現得這麼好。”

The high-fat group followed something of a modified Atkins diet. They were told to eat mostly protein and fat, and to choose foods with primarily unsaturated fats, like fish, olive oil and nuts. But they were allowed to eat foods higher in saturated fat as well, including cheese and red meat.

高脂肪攝入小組所遵循的飲食習慣是一種經過改良的阿特金斯減肥法。按照要求，他們主要攝入蛋白質和脂肪，而且選擇主要含不飽和脂肪的食物，比如魚類、橄欖油和堅果。但是，他們也可以食用奶酪和紅肉等飽和脂肪含量較高的食物。

A typical day’s diet was not onerous: It might consist of eggs for breakfast, tuna salad for lunch, and some kind of protein for dinner — like red meat, chicken, fish, pork or tofu — along with vegetables. Low-carb participants were encouraged to cook with olive and canola oils, but butter was allowed, too.

每天的飲食並不麻煩：可以是早餐吃雞蛋，中餐吃金槍魚沙拉，晚餐攝入某種蛋白質——比如牛羊肉、雞肉、魚肉、豬肉或豆腐——以及一些蔬菜。研究人員建議低碳水化合物小組的成員最好用橄欖油和菜籽油來烹飪，不過也可以食用黃油。

Over all, they took in a little more than 13 percent of their daily calories from saturated fat, more than double the 5 to 6 percent limit recommended by the American Heart Association. The majority of their fat intake, however, was unsaturated fats.

總體而言，他們從飽和脂肪中攝取的熱量佔卡路里日攝入量的13%多一點，超過了美國心臟協會(American Heart Association)推薦的5%到6%限值的兩倍。不過，他們攝入的主要是不飽和脂肪。

The low-fat group included more grains, cereals and starches in their diet. They reduced their total fat intake to less than 30 percent of their daily calories, which is in line with the federal government’s dietary guidelines. The other group increased their total fat intake to more than 40 percent of daily calories.

低脂肪攝入小組的飲食裏包括較多的穀物和澱粉。他們把從脂肪攝取的熱量降到了卡路里日攝入量的30%以下，與聯邦政府推薦的飲食標準相符。另外一組從脂肪攝取的總熱量則超過了他們卡路里日攝入量的40%。

Both groups were encouraged to eat vegetables, and the low-carbohydrate group was told that eating some beans and fresh fruit was fine as well.

研究人員建議兩組成員多吃蔬菜，而且低碳水化合物攝入小組還被告知，食用一些豆類和新鮮水果也沒事。

In the end, people in the low-carbohydrate group saw markers of inflammation and triglycerides — a type of fat that circulates in the blood — plunge. Their HDL, the so-called good cholesterol, rose more sharply than it did for people in the low-fat group.

最後，低碳水化合物攝入小組的成員出現了炎症和甘油三酸脂——一種在血液中循環的脂肪——標記物突降的跡象。與低脂肪攝入小組的成員相比，他們的高密度脂蛋白(HDL)——即“有益膽固醇”——的增加要顯著得多。

Blood pressure, total cholesterol and LDL, the so-called bad cholesterol, stayed about the same for people in each group.

兩組人員的血壓、總膽固醇和低密度脂蛋白(LDL)——即“有害膽固醇”——則大約保持在之前的水平。

Nonetheless, those on the low-carbohydrate diet ultimately did so well that they managed to lower their Framingham risk scores, which calculate the likelihood of a heart attack within the next 10 years. The low-fat group on average had no improvement in their scores.

儘管如此，低碳水化合物攝入小組的成員最後的身體狀態非常棒，以至於他們的弗雷明漢風險評分——評估10年內心肌梗死的發病可能性——也降低了。然而，低脂肪攝入小組的評分則一般沒有改善。

The decrease in risk on the low-carboydrate diet “should translate into a substantial benefit,” said Dr. Allan Sniderman, a professor of cardiology at McGill University in Montreal.

蒙特利爾麥克吉爾大學(McGill University)的心臟病學教授阿蘭·斯奈德曼(Allan Sniderman)稱，低碳水化合物飲食減少患病風險的情況“應該被理解爲能夠帶來相當大的好處”。

One important predictor of heart disease that the study did not assess, Dr. Sniderman said, was the relative size and number of LDL particles in the bloodstream. Two people can have the same overall LDL concentration, but very different levels of risk depending on whether they have a lot of small, dense LDL particles or a small number of large and fluffy particles.

斯奈德曼說，此次研究並沒有評估心臟疾病的一項重要預測指標，即血液中LDL顆粒的相對大小和數量。兩個LDL總體濃度相當的的人，患病風險可能差異很大，這取決於他們的LDL顆粒是數量多、體積小、密度高，還是數量少、體積大、密度低。

Eating refined carbohydrates tends to raise the overall number of LDL particles and shift them toward the small, dense variety, which contributes to atherosclerosis. Saturated fat tends to make LDL particles larger, more buoyant and less likely to clog arteries, at least when carbohydrate intake is not high, said Dr. Ronald M. Krauss, the former chairman of the American Heart Association’s dietary guidelines committee.

食用精煉碳水化合物可能會增加LDL顆粒的整體數量，並把它們變成體積小、密度高的類型。這可能會對動脈硬化起到促進作用。美國心臟協會膳食指南委員會前主席羅納爾·M·克勞斯博士(Ronald M. Krauss)稱，至少當碳水化合物的攝入量不高時，飽和脂肪可能會使LDL粒子變得更大、密度更低，從而降低堵塞動脈的可能性。

Small, dense LDL is the kind typically found in heart patients and in people who have high triglycerides, central obesity and other aspects of the so-called metabolic syndrome, said Dr. Krauss, who is also the director of atherosclerosis research at Children’s Hospital Oakland Research Institute.

克勞斯說，體積小、密度高的LDL在心臟病患者和那些甘油三酸脂偏高、罹患向心性肥胖等“代謝綜合徵”的人羣身上很常見。他目前還在奧克蘭兒童醫院研究中心(Children’s Hospital Oakland Research Institute)擔任動脈硬化研究的負責人。

“I’ve been a strong advocate of moving saturated fat down the list of priorities in dietary recommendations for one reason: because of the increasing importance of metabolic syndrome and the role that carbohydrates play,” Dr. Krauss said.

克勞斯說，“我強烈建議把飽和脂肪從飲食禁忌的清單上往後移，只爲一個原因：因爲代謝綜合徵的重要性日益增加，以及碳水化合物在其中起到的作用。”

Dr. Mozaffarian said the research suggested that health authorities should pivot away from fat restrictions and encourage people to eat fewer processed foods, particularly those with refined carbohydrates.

莫扎法裏安表示，新研究說明，衛生部門應該把注意力從限制脂肪攝入量上轉移開來，鼓勵人們少食用加工食品，尤其是那些含有提煉碳水化合物的食品。

The average person may not pay much attention to the federal dietary guidelines, but their influence can be seen, for example, in school lunch programs, which is why many schools forbid whole milk but serve their students fat-free chocolate milk loaded with sugar, Dr. Mozaffarian said.

莫扎法裏安說，普通人可能不會太過關注聯邦飲食指南，但它們的影響在學校的午餐計劃等方面顯而易見。這就是爲什麼許多學校都不提供全脂牛奶，轉而提供加了很多食糖的脫脂巧克力奶。