健康饮食结构 低淀粉高脂肪

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.

一项重大的新研究显示，比起那些遵循卫生部门数十年来一直推崇的低脂饮食的人，不吃碳水化合物但摄入较多脂肪、乃至饱和脂肪的人，消耗的体脂更多，并且罹患心血管疾病的风险更低。

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.

长期以来，关于哪种食物对减重和身体健康最有好处一直存在争议，上述结论不太可能成为定论。几十年前，通过比较全国大量人口的患病率，人们形成了膳食脂肪、尤其是饱和脂肪对人体有害的概念。

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，通过在一段时间内评估个人及其饮食习惯，近期的临床研究描绘出了一幅更为复杂的画面。有些研究提供了非常有力的证据显示，人们可以通过摄入较少的碳水化合物和较多的膳食脂肪——反式脂肪除外——来大幅度降低罹患心脏疾病的风险。这些新的发现说明，这种做法能更有效地减少体脂，并同时减轻体重。

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.

这项新研究由美国国立卫生研究院(National Institutes of Health)出资，成果发表在了《内科学年鉴》(Annals of Internal Medicine)上。调查对象包括各个族裔的150名男女——这在临床营养研究中并不多见。按照指派的结果，这些人必须在一年内遵守限制碳水化合物或脂肪摄入量的饮食要求，但无需限制总体的卡路里摄入量。

“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.”

“据我所知，这属于首批不限制卡路里摄入的饮食方式长期试验，”塔夫茨大学弗里德曼营养科学与政策学院(Friedman School of Nutrition Science and Policy at Tufts University)院长达柳什·莫扎法里安(Dariush Mozaffarian)说。他没有参与这项新研究。“这表明，在可以想吃什么就吃什么的情况下，减少碳水化合物的摄入有助于减轻体重，而且还不需要关注卡路里。这一点很重要，因为与努力减少卡路里摄入相比，人们更容易改变饮食的种类。”

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世纪70年代，罗伯特·阿特金斯博士(Robert Atkins)开始推行低碳水化合物高脂高蛋白饮食以来，此类减肥方式就开始被广泛采用。一直有批评声认为，这种饮食习惯减去的是人体的水份，而不是脂肪，而且胆固醇等心脏疾病的风险因素也会随之攀升，因为人们食用了更多的肉类和奶制品，必然会增加饱和脂肪的摄入量。

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.”

上述新研究论文的第一作者、杜兰大学公共卫生及热带疾病学院(Tulane University School of Public Health and Tropical Medicine)的莉迪娅·A·巴扎诺博士(Lydia A. Bazzano)表示，许多营养学专家和卫生部门都“大力反对”低碳水化合物的饮食方式。“他们总是认为，你的饱和脂肪摄入量肯定会增加，然后你的胆固醇就会升高，”她说。“接下来，通常会带来不良后果。”

The new study showed that was not the case.

这项新研究表明，事实并非如此。

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.

在为期一年的试验结束时，低碳水化合物摄入小组的成员体重，比低脂肪小组平均多减了8磅左右（约合3.6公斤）。与后者相比，他们的体脂减少量明显更大，而且精瘦肌肉量也增加了——虽然两组受试人员均没有改变身体活动量。

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

尽管低脂肪摄入小组的成员的确减轻了体重，但他们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.”

“他们减去的其实是精瘦肌肉，这并不好，”莫扎法里安说。“肌肉量与脂肪量的平衡要比体重本身重要得多。这是一个非常重要的发现，说明了为什么低碳水化合物、高脂肪摄入的小组在代谢方面会表现得这么好。”

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.

高脂肪摄入小组所遵循的饮食习惯是一种经过改良的阿特金斯减肥法。按照要求，他们主要摄入蛋白质和脂肪，而且选择主要含不饱和脂肪的食物，比如鱼类、橄榄油和坚果。但是，他们也可以食用奶酪和红肉等饱和脂肪含量较高的食物。

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.

每天的饮食并不麻烦：可以是早餐吃鸡蛋，中餐吃金枪鱼沙拉，晚餐摄入某种蛋白质——比如牛羊肉、鸡肉、鱼肉、猪肉或豆腐——以及一些蔬菜。研究人员建议低碳水化合物小组的成员最好用橄榄油和菜籽油来烹饪，不过也可以食用黄油。

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.

总体而言，他们从饱和脂肪中摄取的热量占卡路里日摄入量的13%多一点，超过了美国心脏协会(American Heart Association)推荐的5%到6%限值的两倍。不过，他们摄入的主要是不饱和脂肪。

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.

低脂肪摄入小组的饮食里包括较多的谷物和淀粉。他们把从脂肪摄取的热量降到了卡路里日摄入量的30%以下，与联邦政府推荐的饮食标准相符。另外一组从脂肪摄取的总热量则超过了他们卡路里日摄入量的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.

研究人员建议两组成员多吃蔬菜，而且低碳水化合物摄入小组还被告知，食用一些豆类和新鲜水果也没事。

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.

最后，低碳水化合物摄入小组的成员出现了炎症和甘油三酸脂——一种在血液中循环的脂肪——标记物突降的迹象。与低脂肪摄入小组的成员相比，他们的高密度脂蛋白(HDL)——即“有益胆固醇”——的增加要显著得多。

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

两组人员的血压、总胆固醇和低密度脂蛋白(LDL)——即“有害胆固醇”——则大约保持在之前的水平。

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.

尽管如此，低碳水化合物摄入小组的成员最后的身体状态非常棒，以至于他们的弗雷明汉风险评分——评估10年内心肌梗死的发病可能性——也降低了。然而，低脂肪摄入小组的评分则一般没有改善。

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.

蒙特利尔麦克吉尔大学(McGill University)的心脏病学教授阿兰·斯奈德曼(Allan Sniderman)称，低碳水化合物饮食减少患病风险的情况“应该被理解为能够带来相当大的好处”。

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.

斯奈德曼说，此次研究并没有评估心脏疾病的一项重要预测指标，即血液中LDL颗粒的相对大小和数量。两个LDL总体浓度相当的的人，患病风险可能差异很大，这取决于他们的LDL颗粒是数量多、体积小、密度高，还是数量少、体积大、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.

食用精炼碳水化合物可能会增加LDL颗粒的整体数量，并把它们变成体积小、密度高的类型。这可能会对动脉硬化起到促进作用。美国心脏协会膳食指南委员会前主席罗纳尔·M·克劳斯博士(Ronald M. Krauss)称，至少当碳水化合物的摄入量不高时，饱和脂肪可能会使LDL粒子变得更大、密度更低，从而降低堵塞动脉的可能性。

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.

克劳斯说，体积小、密度高的LDL在心脏病患者和那些甘油三酸脂偏高、罹患向心性肥胖等“代谢综合征”的人群身上很常见。他目前还在奥克兰儿童医院研究中心(Children’s Hospital Oakland Research Institute)担任动脉硬化研究的负责人。

“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.

克劳斯说，“我强烈建议把饱和脂肪从饮食禁忌的清单上往后移，只为一个原因：因为代谢综合征的重要性日益增加，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.

莫扎法里安表示，新研究说明，卫生部门应该把注意力从限制脂肪摄入量上转移开来，鼓励人们少食用加工食品，尤其是那些含有提炼碳水化合物的食品。

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.

莫扎法里安说，普通人可能不会太过关注联邦饮食指南，但它们的影响在学校的午餐计划等方面显而易见。这就是为什么许多学校都不提供全脂牛奶，转而提供加了很多食糖的脱脂巧克力奶。