低脂還是低碳水,怎麼吃才能減肥?

The endless array of diets that claim to help you shed pounds tend to fAll into two camps: low fat or low carbohydrate. Some companies even claim that genetics can tell us which diet is better for which people.

聲稱能幫助你減肥的飲食方式不計其數，它們往往分爲兩大陣營：低脂或低碳水化合物。一些公司甚至聲稱基因可以告訴我們哪種飲食更適合哪些人。

A rigorous recent study sought to settle the debate, and it had results to disappoint both camps. On the hopeful side, as The New York Times noted, people managed to lose weight no matter which of the two diets they followed.

最近，一項嚴謹的研究試圖解決這場爭論。研究得出的結果讓兩個陣營都失望了。樂觀的一面是，正如《紐約時報》所指出的那樣，兩種飲食方式無論遵循哪一種都能減肥。

The study is worth a closer look to see what it did and did not prove.

這項研究值得我們去細究它證明了什麼，沒有證明什麼。

Researchers at Stanford University took more than 600 people (which is huge for a nutrition study) aged 18 to 50 who had a body mass index of 28 to 40 (25-30 is overweight, and 30 and over is obese). The study subjects had to be otherwise healthy. They couldn’t even be on statins, or drugs for Type 2 diabetes or hypertension, which might affect weight or energy expenditure. They were all randomly assigned to a healthful low-fat or a healthful low-carbohydrate diet, and they were clearly not blinded to which group they were in.

斯坦福大學(Stanford University)的研究人員挑選了600多名（這個數字對營養學研究來說堪稱巨大）年齡在18到50歲，身體質量指數在28到40之間（25到30之間爲超重，30或以上爲肥胖）的研究對象。他們在其他方面必須保持健康，甚至不能服用他汀類藥物，也就是治療2型糖尿病或高血壓的藥物。這些藥物可能會影響體重或能量消耗。所有人被隨機分到健康低脂飲食組或健康低碳水化合物飲食組，但他們顯然不知道自己屬於哪一個組。

All participants attended 22 instructional sessions over one year in groups of about 17 people. The sessions were held weekly at first and were then spaced out so that they were monthly in the last six months. Everyone was encouraged to reduce intake of the avoided nutrient to 20 grams per day over the first eight weeks, then participants slowly added fats or carbohydrates back to their diets until they reached the lowest level of intake they believed could be sustained for the long haul.

在一年時間裏，所有參與者以大約17人一個小組的形式上了22次指導課。這些課程一開始每週一次，然後拉開間距，到最後六個月變成每月一次。在前八週，每個人都被鼓勵將應避免的營養物質的攝入量降低到一天20克，然後參與者慢慢恢復各自飲食中的脂肪或碳水化合物攝入量，直到達到他們認爲可以長期維持的最低攝入量。

Everyone was followed for a year (which is an eternity for a nutrition study). Everyone was encouraged to maximize vegetable intake; to minimize added sugar, refined flour and trans fat intake; and to focus on whole foods that were minimally processed. The subjects were also encouraged to cook at home as much as possible.

每個實驗對象都被追蹤了一年（這對營養學研究來說這是很長一段時間）。所有人都被鼓勵儘量多攝入蔬菜，少攝入添加糖、精製麪粉和反式脂肪酸，並重點食用簡單加工的全天然食物。實驗對象還被鼓勵儘可能在家做飯。

All the participants took a glucose tolerance test as a measurement of insulin sensitivity. Some believe that insulin resistance or sensitivity may affect not only how people respond to diets, but also how well they adhere to them. The participants were also genotyped, because some believe that certain genes will make people more sensitive to carbohydrates or fat with respect to weight gain. About 40 percent of participants had a low-fat genotype, and 30 percent had a low-carbohydrate genotype.

所有參與者都接受了葡萄糖耐量測試，以衡量他們的胰島素敏感性。一些人認爲，胰島素抵抗或敏感性不僅會影響人們對飲食方式的反應，還會影響他們對飲食方式的堅持情況。參與者還接受了基因分型，因爲一些人認爲，就體重增加而言，某些基因會使人們對碳水化合物或脂肪更敏感。大約40%的參與者屬於低脂基因型，30%屬於低碳水化合物基因型。

Data were gathered at the beginning of the study, at six months and at one year. At three unannounced times, researchers checked on patients to see how closely they were sticking to the instructions.

研究過程中收集了三次數據，分別是研究開始、六個月和一年時。研究人員分三次在不事先通知的情況下查看患者嚴格遵守指導的情況。

This was a phenomenally well-designed trial.

這是一項設計得極爲出色的試驗。

People did change their diets according to their group assignment. Those in the low-fat group consumed, on average, 29 percent of their calories from fats, versus 45 percent in the low-carbohydrate group. Those in the low-carbohydrate group consumed 30 percent of their calories from carbohydrates, versus 48 percent in the low-fat group.

人們的確會根據分組改變自己的飲食。低脂組的人消耗的熱量平均29%來自脂肪，低碳水組的人45%的熱量來自脂肪。低碳水組消耗的熱量30%來自碳水化合物，低脂組48%的熱量來自碳水化合物。

They did not, however, lose meaningfully different amounts of weight. At 12 months, the low-carbohydrate group had lost, on average, just over 13 pounds, compared with more than 11.5 pounds in the low-fat group. The difference was not statistically significant.

然而，他們的體重減少並沒有什麼實質性的不同。在12個月時，低碳水組平均只減了13磅多一點，對比低脂組減少了超過11.5磅。該差異沒有統計學意義。

Insulin sensitivity didn’t make a difference. People who secreted more or less insulin lost no more or less weight in general on either a low-fat or low-carbohydrate diet. Genetics didn’t make a difference either. People who had genes that might indicate that they would do better on one diet or the other didn’t.

胰島素敏感性並沒有影響。人們分泌的胰島素不論多少，在低脂或低碳水飲食中的減重差別都不大。基因也沒什麼差別。一些人有的基因可能意味着他們會在某類飲食中表現更好，而在另一種飲食中則沒那麼好。

In fact, when you look at how every single participant in this study fared on the diet to which he or she was assigned, it’s remarkable how both diets yielded an almost identical, curving range of responses — from lots of weight lost to a little gained. It wasn’t just the averages.

事實上，如果觀察研究中每個單一參與者根據自己所分配到的飲食進食，人們會驚訝於兩種進食都產生了幾乎相同的曲線反應範圍——從大幅減重的到輕微增重的。不僅僅是平均數。

Some have taken this study to prove that avoiding processed foods, eating more whole foods, and cooking at home leads to weight loss. While I’d like that to be true — I have advocated this healthful approach in my Upshot article on food recommendations and in a recent book — that’s not what this study showed. Although that advice was given to all participants, there was no control group in which that advice was omitted, and so no conclusions can be made as to the efficacy of these instructions.

一些人用這項研究證明，避開加工食品、吃更多天然食品並且在家下廚就能減肥。雖然我希望這是真的——在“結語”(Upshot)專欄有關食物的文章以及最近的一本書中，我都提倡過這種健康的方法——但本次研究並未表現出這一點。雖然所有參與者都得到了這一建議，但並沒有未得到該項建議的對照組，因此，不能得出有關這些建議是否有效的結論。

Others have taken this study as evidence debunking the idea that counting calories is the key to weight loss. While that wasn’t the main thrust of this study, nor the instructions given, participants did reduce their intake by an average of 500-600 calories a day (even if they didn’t count them). This study didn’t prove the unimportance of calories.

有人用這項研究來駁斥卡路里是減肥關鍵的說法。雖然這不是研究的主要目的，給出的指示裏也沒有，但參與者每天確實減少了500到600卡路里的攝入量（即使他們沒在計算）。這項研究不能證明卡路里不重要。

The researchers also asked everyone, not just those in the low-carb group, to avoid “added sugars.” Therefore, we can’t really say anything new about added sugars and weight loss.

研究人員還要求所有人避免“添加糖”，而不只是只對低碳水化合物組有這個要求。因此，對於添加糖和減肥的關係我們並沒有什麼新消息。

What this study does show is that people who have staked a claim on one diet’s superiority over another don’t have as strong a case as they think. It’s hard to overstate how similarly these two diets performed, even at an individual level.

這項研究能夠表明的是，那些主張某種飲食比另一種飲食更好的人，或許不像他們所想的那麼有理有據。即使是在個人層面，這兩種飲食的表現之相似是毫無疑問的。

It shows us that the many people, and the many studies, suggesting that we can tell which diets are best for you based on genetics or based on insulin levels might not be right either. Almost all of the studies that backed up such ideas were smaller, of shorter duration or less robust in design than this one. Granted, it’s still possible that there might be some gene discovered in the future that makes a difference, but those who think they’ve found it already might want to check their enthusiasm.

它也向我們表明，許多人和許多研究認爲我們能根據基因或胰島素水平來判斷哪種飲食對你有益，可能也是不對的。幾乎所有支持這些想法的研究都規模較小、時間跨度更短或設計方案魯棒性不足。誠然，未來仍有可能發現一些能產生影響的基因，但那些覺得自己已經發現了這個基因的人，可能需要再考慮考慮了。

This study was focused mostly on people who were obese, so people looking to lose just a few pounds might benefit more from one diet or the other; we don’t know. It’s also worth noting that the people in this study received significant support on both diets, so the results seen here might not apply to those attempting to lose weight on their own.

這項研究主要關注那些肥胖的人，所以我們不知道想要減掉幾磅體重的人會從哪種飲食上獲益更多。同樣值得注意的是，這項研究的參與者不管採用哪種飲食方式都獲得了大量支持，所以它的結果可能並不適用於那些試圖自己減肥的人。

You should be wary of those who tell you that they know what diet is best for you, or that there’s a test out there to tell you the same. Successful diets over the long haul are most likely ones that involve slow and steady changes. The simplest approach — and many have espoused it, including Jane Brody recently here at The Times — is to cut out processed foods, think about the calories you’re drinking, and try not to eat more than you intend to.

如果有些人對你說，他們知道什麼樣的飲食最適合你，或者有個測試能幫你測出來，對此你要保持警惕。緩慢而穩定的改變才最有可能保證長期節食的成功。最簡單的方法是減少食用加工食品，留意你從飲料中攝入了多少卡路里，儘量不要吃得比你打算吃的多。很多人都贊成這種方式，包括最近在時報上發表文章的簡·布羅迪(Jane Brody)。

The bottom line is that the best diet for you is still the one you will stick to. No one knows better than you what that diet might be. You’ll most likely have to figure it out for yourself.

最重要的是，最適合你的飲食仍然是你能堅持下去的飲食。沒有人比你更清楚你最適合哪種飲食。你很可能需要自己去弄清楚。