Low Carb? Low Fat? What Latest Dieting Studies Tell Us

低卡還是低脂？最新飲食研究說分明

Bacon and black coffee for breakfast, or oatmeal and bananas?

早餐吃培根喝黑咖啡，還是喝燕麥粥配香蕉好呢？

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Low Carb? Low Fat? What Latest Dieting Studies Tell Us
VOA News
January 01, 2019 5:14 PM Associated Press (source)

Low Carb? Low Fat? What Latest Dieting Studies Tell Us

低卡還是低脂？最新飲食研究說分明

January 01, 2019 5:14 PM

Associated Press

New York —

Bacon and black coffee for breakfast, or oatmeal and bananas?

If you're planning to try to lose weight in 2019, you're sure to find a fierce debate online and among friends and family about how best to do it. It seems like everyone has an opinion, and new fads emerge every year.

Two major studies last year provided more fuel for a particularly polarizing topic — the role carbs play in making us fat. The studies gave scientists some clues, but, like other nutrition studies, they can't say which diet — if any — is best for everyone.

That's not going to satisfy people who want black-and-white answers, but nutrition research is extremely difficult and even the most respected studies come with big caveats. People are so different that it's all but impossible to conduct studies that show what really works over long periods of time.

Before embarking on a weight loss plan for the new year, here's a look at some of what was learned last year.

Fewer carbs, fewer pounds?

It's no longer called the Atkins Diet, but the low-carb school of dieting has been enjoying a comeback. The idea is that the refined carbohydrates in foods like white bread are quickly converted into sugar in our bodies, leading to energy swings and hunger.

By cutting carbs, the claim is that weight loss will be easier because your body will instead burn fat for fuel while feeling less hungry. A recent study seems to offer more support for low-carb proponents. But, like many studies, it tried to understand just one sliver of how the body works.

The study, co-led by an author of books promoting low-carb diets, looked at whether varying carb levels might affect how the body uses energy. Among 164 participants, it found those on low-carb diets burned more total calories than those on high-carb diets.

The study did not say people lost more weight on a low-carb diet — and didn't try to measure that. Meals and snacks were tightly controlled and continually adjusted so everyone's weights stayed stable.

David Ludwig, a lead author of the paper and researcher at Boston Children's Hospital, said it suggests limiting carbs could make it easier for people to keep weight off once they've lost it. He said the approach might work best for those with diabetes or pre-diabetes.

Ludwig noted the study wasn't intended to test long-term health effects or real-world scenarios where people make their own food. The findings also need to be replicated to be validated, he said.

Caroline Apovian of Boston University's School of Medicine said the findings are interesting fodder for the scientific community, but that they shouldn't be taken as advice for the average person looking to lose weight.

Do I avoid fat to be skinny?

For years people were advised to curb fats, which are found in foods including meat, nuts, eggs, butter and oil. Cutting fat was seen as a way to control weight, since a gram of fat has twice as many calories than the same amount of carbs or protein.

Many say the advice had the opposite effect by inadvertently giving us license to gobble up fat-free cookies, cakes and other foods that were instead full of the refined carbs and sugars now blamed for our wider waistlines.

Nutrition experts gradually moved away from blanket recommendations to limit fats for weight loss. Fats are necessary for absorbing important nutrients and can help us feel full. That doesn't mean you have to subsist on steak drizzled in butter to be healthy.

Bruce Y. Lee, a professor of international health at Johns Hopkins, said the lessons learned from the anti-fat fad should be applied to the anti-carb fad: Don't oversimplify advice.

"There's a constant look for an easy way out," Lee said.

Which is better?

Another big study this past year found low-carb diets and low-fat diets were about equally as effective for weight loss. Results varied by individual, but after a year, people in both groups shed an average of 12 to 13 pounds.

The author noted the findings don't contradict Ludwig's low-carb study. Instead, they suggest there may be some flexibility in the ways we can lose weight. Participants in both groups were encouraged to focus on minimally processed foods like produce and meat prepared at home. Everyone was advised to limit added sugar and refined flour.

"If you got that foundation right, for many, that would be an enormous change," said Christopher Gardner of Stanford University and one of the study's authors.

Limiting processed foods could improve most diets by cutting down overall calories, while still leaving wiggle room for people's preferences. That's important, because for a diet to be effective, a person has to be able to stick to it. A breakfast of fruit and oatmeal may be filling for one person, but leave another hungry soon after.

Gardner notes the study had its limitations, too. Participants' diets weren't controlled. People were instead instructed on how to achieve eating a low-carb or low-fat in regular meetings with dietitians, which may have provided a support network most dieters don't have.

What works?

In the short term you can probably lose weight by eating only raw foods, or going vegan, or cutting out gluten, or following another diet plan that catches your eye. But what will work for you over the long term is a different question.

Zhaoping Li, director of clinical nutrition division at the University of California, Los Angeles, says there is no single set of guidelines that help everyone lose weight and keep it off. It's why diets often fail — they don't account for the many factors that drive us to eat what we do.

To help people lose weight, Li examines her patients' eating and physical activity routines to identify improvements people will be able to live with.

"What sticks is what matters," Li said.

早餐吃培根喝黑咖啡，還是燕麥粥(oatmeal)配香蕉好呢？

如果你打算在 2019 年減重，那麼肯定能在網路上及親朋好友間見到關於最佳減重方式熱烈(fierce)的討論。大家對於如何減重似乎都有自己的一套看法，而且每年都會興起(emerge)新的減重熱潮(fad)。

長久以來，碳水化合物(carb)是否導致肥胖是個非常兩極化(polarize)的主題，而去年（編按：2018 年）的兩項重要飲食研究為這主題增添了更多話題性。不過，如同其他營養(nutrition)研究，這兩份研究提供了科學家一些線索(clue)，卻無法指出哪一種飲食（如果有的話）對大眾最好。

這樣的結果勢必無法滿足想要黑白分明(black-and-white)答案的人。然而，營養研究的進行非常困難，即便是最被看重的研究也伴隨著很多限制(caveat)。畢竟形形色色的大眾如此不同，以致於幾乎(all but)不可能研究出可以長期依循的減重模式。

開始著手(embark on . . .)新年減重計畫前，先來瞧瞧去年相關研究給了我們什麼啟示吧！

少點碳水化合物，體重會輕點？

儘管不再稱作「阿金飲食法（Atkins Diet）」，低碳水化合物飲食（以下簡稱「低碳飲食」）學派目前正有東山再起(comeback)之勢。這種學派著重的概念在於食品（例如：白麵包）中精製的(refined)碳水化合物(carbohydrate)在人體內會迅速轉變成(convert . . . into . . .)糖分，進而引起(lead to)能量變化(swing)和飢餓感。

低碳飲食主張透過減少碳水化合物的攝取讓減重更容易，原因在於身體會轉而燃燒脂肪而非醣類，同時減少飢餓感。近來一份研究結果似乎更加支持低碳飲食的擁護者(proponent)。然而，這份研究如同其他研究般，僅能讓我們了解人體運作的一小部分而已。

這份由出版多本推廣低碳飲食書籍的作者共同主持的研究探討了不同的(varying)碳水化合物攝取量是否會影響人體對於能量的運用。研究顯示，164 位受試者中，低碳飲食者比高碳飲食（high-carb diet）者燃燒了更多卡路里（calorie，測量食物所含熱量的單位）。

研究並未表明低碳飲食者體重變得更輕，也未曾試圖測量他們的體重變化。受試者的三餐和零食都經過嚴格控管並持續調整(adjust)以便讓所有人的體重維持平穩。

美國波士頓兒童醫院（Boston Children's Hospital）研究員大衛．路德維格（David Ludwig）醫師是這份研究報告的主要作者。他說，研究結果顯示出限制碳水化合物的攝取或許能讓減重者更輕易地保持身材不復胖，同時表示這種飲食法最適合糖尿病(diabetes)或糖尿病前期(pre-diabetes)的患者。

路德維格醫師指出，這項研究並不打算檢視對健康的長期效益或是人們可以自己準備餐點的現實(real-world)情境(scenario)。他表示，這些研究結果仍需經過重複(replicate)試驗才能證實(validate)。

美國波士頓大學（Boston University）醫學院教授卡洛琳．阿波維安（Caroline Apovian）表示，這些研究結果提供科學界有趣的研究題材(fodder)，但不該當作一般人減重的建議。

為了瘦一點，需要避免攝取脂肪嗎？

長久以來專家建議大眾要控制(curb)脂肪的攝取量，食物中包括肉類、堅果、蛋、奶油和食用油等都含有脂肪。減少脂肪攝取以往被視為控制體重的方法，原因在於一公克的脂肪比等量的碳水化合物或蛋白質(protein)多了一倍的卡路里。

很多人說這樣的建議無意間(inadvertently)給了我們肆無忌「啖」(gobble up)零脂肪(fat-free)餅乾、蛋糕和其他精緻食品的藉口，然而這些食品卻充滿了會讓我們腰圍更粗的精製碳水化合物與糖分，因而產生反效果。

營養專家在減重議題的處理上，逐漸從原本建議完全(blanket)不攝取油脂轉向建議限制油脂的攝取量。油脂對於重要營養素(nutrient)的吸收(absorb)不可或缺，還能帶來飽足感，但這並不表示必須吃淋(drizzle)了奶油的肉片來維持健康。

美國約翰．霍普金斯大學（Johns Hopkins University）國際衛生學系教授布魯斯．李（Bruce Y. Lee）表示，從反脂肪風潮中學到的教訓應當運用於(apply to . . .)反碳水化合物的風潮，那就是：切勿將建議過度簡化(oversimplify)。

李教授說：「減重並沒有那麼簡單。」

〔編按：本句字面之原意為「人們會不斷地藉著簡化專家的建議來為自己找尋較容易的減重方式。」〕 

哪個比較好？

去年另一項大型研究發現，低碳飲食和低脂飲食兩者減重的效果差不多。其成效因人而異，但一年之後，參與研究的兩組受試者都平均甩掉(shed)了 12 至 13 磅（1 磅約 0.45 公斤）。

這份研究報告的作者指出，研究結果並未與路德維格醫師的低碳水化合物研究相悖(contradict . . .)。相反地，這些結果似乎顯示出減重方式也許可以有些彈性(flexibility)。研究鼓勵兩組受試者飲食上要以加工(processed)最少的食物為主，例如農產品(produce)或在家自行烹調準備的肉類料理，並建議所有人要限制額外糖分和精製麵粉的攝取。

「對很多人來說，建立正確的飲食基礎(foundation)會帶來極大的(enormous)改變。」美國史丹佛大學（Stanford University）教授克里斯多福．加德納（Christopher Gardner）說道。他也是這份研究報告的作者之一。

透過限制加工食品的攝取減少總熱量的吸收能夠改善大部分的飲食方式，同時還保留了一些可以依喜好選擇食物的轉圜餘地(wiggle room)。這對減重者而言很重要，因為節食必須在減重者能夠堅持(stick to)下去的情況下才有效。早餐吃水果和燕麥粥也許可以讓一個人有飽足感(filling)，卻可能讓另一人很快就餓了。

加德納教授指出，這份研究仍有其局限性(limitation)。受試者的日常飲食並未受到控制，而是改以和營養師(dietitian)定期會面、接受指導(instruct)來達到低碳水化合物或低脂的飲食模式。然而，大部分節食者卻沒有這樣可供定期諮詢的支援團隊。

什麼才有效？

短期內也許可以藉由只吃未經加工的(raw)食物，或奉行嚴格素食主義(vegan)，或避免攝取麩質(gluten)，或是依循另一套引起關注的飲食法等方式減重。不過，該怎麼做才是長久之計就另當別論了。

美國加州大學洛杉磯分校（University of California, Los Angeles，UCLA）醫學院臨床營養科主任李兆平（Zhaoping Li）表示，沒有單一的準則(guideline)可以幫助所有人減重且不復胖。節食減重常失敗的原因在於各種節食方法並未將許多驅使我們選擇某些食物的因素納入考量。

〔編按：原新聞中，本段（新聞第 24 段／倒數第 3 段）的 "account for" 似乎為誤植，請參考紐約時報（The New York Times）於 2019 年 1 月 1 日之報導 Low Carb? Low Fat? What the Latest Dieting Studies Tell Us 一文中倒數第 3 段 ". . . It's why diets often fail — they don't factor into account the many factors that drive us to eat what we do."。〕

為了幫助病患減重，李主任仔細調查他們例行的飲食和活動常態，以便找出可以讓他們持續進步的生活模式。

李主任強調：「能堅持才是重點。」

〔編按：本篇新聞相關報導請參考史丹佛大學醫學院新聞中心（News Center at Stanford University School of Medicine）於 2018 年 2 月 20 日的報導 Low-fat or low-carb? It's a draw, study finds。〕