「脂肪」被冤50年 肥胖、心臟病並不怪它

原作者:Justina Reichel

幾十年來,我們一直遵循這樣的黃金法則:把吃下的熱量燃燒掉,以維持健康體重。於是人們認爲超重完全是個人的錯誤,是不守飲食規則、意志力不足、懶惰或貪吃造成的結果。

但近年來,越來越多的科學家和新聞記者提出肥胖危機的原因遠遠超過我們自身:糟糕的營養科學、不良食品政策、還有長期來自政府和營養專家的錯誤信息。也就是說,肥胖不(全)是我們自己的錯。

這些科學家和記者認為,過去半個世紀以來,正是我們接受的飲食建議為肥胖症創造了條件,造成了肥胖症的大流行。

脂肪怎麼成為「罪魁禍首」?

脂肪的倡導者們認爲,關於脂肪之謎的癥結在於,自20世紀70年代以來,脂肪似妖魔的觀念就開始植入我們心中。

事情始於1955年9月24日美國總統艾森豪威爾的心臟病發作。當時美國中年男子心臟病發病率一直在上升,總統患病將這個問題推到最醒目的位置。

當研究人員們爭相尋找病因時,一個有魅力又鬥志旺盛的美國生理學家Ancel Keys提出了一個假說:黃油、紅肉、雞蛋和奶酪等食物中飽和脂肪,才是罪魁禍首!他的話聽起來完全符合邏輯:吃脂肪讓人長胖。

到20世紀70年代,Keys的理論已經在營養專家中占據了主導地位,儘管證據不足、研究相互矛盾──有些研究指出糖是「犯人」,而不是脂肪。

隨著脂肪論戰的發起,膳食指南改變了,食物金字塔被引入。基於「1卡熱量 = 1卡熱量」的想法,食物金字塔建議將所有脂肪攝入降到最低,因爲比起碳水化合物等其它主要營養物質,脂肪含兩倍的熱量。這種方法建議人們以低脂肪、高碳水化合物食物為主,每天可食用11份穀類食物,如麵包和麵食。

同時,食品企業紛紛抓住市場,製造脫脂產品,推廣「健康」食品,如低脂麥片、餅乾、沙拉醬等。但他們也知道給食品脫脂意味著失掉味道。怎樣解決這個問題?加糖。

奶酪、黃油這樣的飽和脂肪被列入敵人列表,代替它們的是含有新的「有利心臟健康」的脂肪產品,例如由經化學加工植物油(又稱為氫化油)製成的人造黃油。(這些含有反式脂肪的油正在面臨廣泛的抵制,因為我們越來越多地了解它們的危害。在2015年,FDA確定反式脂肪歸類爲「通常不被認為是安全的」,並規定在三年時間內從所有加工食品中除去反式脂肪。)

記者Nina Teicholz在她關於脂肪的書《 一個關於脂肪的大驚喜:為什麼黃油、肉和奶酪屬於健康飲食》中寫道:「長久以來,脂肪和飽和脂肪不健康的觀點在我們的國民討論中已經根深蒂固,我們傾向於將它認為是『常識』,而非一個具體假設。 」

「但是,像其它飲食與疾病之間關聯的觀點一樣,這一觀點,也是由一組研究人員的一個想法開始,而它的最初來源卻隨著時間的流逝被人們模糊了。」

雖然西方社會大部分採用這種新的低脂肪、熱量計數的方法,用精製碳水化合物代替膳食脂肪,但是我們卻變得越來越胖。自20世紀70年代以來,肥胖症增加了200%。美國的死亡人口中,三分之二是肥胖、糖尿病相關疾病造成。

卡路里都一樣嗎?

堅果等熱量密度高的食物似乎可以預防肥胖、糖尿病和心臟病。(Shutterstock)

「吃一份熱量,消耗一份熱量」和「少吃多動」的古老格言,長期來講對大多數人並不奏效。多鍛煉有很多好處,但減體重常常不是其中的好處之一,因為鍛煉讓人更餓。而且通過鍛鍊消耗不健康飲食幾乎不可能,要消耗掉一個甜甜圈,你需要快走近一個小時。

精確計算每天吃進去的卡路里量,並與你燃燒的卡路里量比較,這是非常有挑戰性的。一個小小的計算失誤就可能讓你一年內增加幾磅體重。即使你成功地限制了卡路里攝入,當「飢餓模式」啓動,你的身體也會向你反擊。

根據卡路里理論,吃少量杏仁與喝一罐可樂是一樣的,因為卡路里計數相似;而低脂餅乾和無脂肪的高糖酸奶都是健康選擇。

哈佛大學醫學院肥胖專家、兒科教授David Ludwig博士在新書《總覺得餓?征服慾望、重煉脂肪細胞、永久減肥(Always Hungry? Conquer Cravings, Retrain Your Fat Cells, and Lose Weight Permanently)》 中說:「最近的研究表明,高度加工的碳水化合物對人體代謝和體重都有不利影響,這種影響無法單獨以卡路里含量解釋。相反,堅果、橄欖油和黑巧克力,一些熱量密度高的食物卻似乎可以預防肥胖、糖尿病和心臟病。」

Ludwig博士被時代雜誌評為「肥胖鬥士」,他與其他醫生如Robert Lustig,David Perlmutter和Mark Hyman,以及Teicholz和Gary Taubes等記者一起,介紹了一種新的理論:我們變胖不是因爲吃脂肪或熱量過多的緣故,是因爲吃糖和精製碳水化合物,它們被快速消化並引起胰島素釋放。這種反應促進身體中的脂肪儲存,並因爲胰島素水平的驟然升高和下降,而引發暴飲暴食的惡性循環。

根據這一想法,沒有了糖和快速消化的碳水化合物(在身體看來後者跟糖沒兩樣),你就不會變胖。

反糖十字軍的Lustig,在他受歡迎的YouTube視頻《糖:苦澀的真相(Sugar: The Bitter Truth)》中說:「並非你吃了什麼,你就多了些什麼。重點是你吃的食物在身體裡發生了怎樣的變化。 」

Hyman在《吃脂肪變瘦(Eat Fat, Get Thin)》一書中指出,專注於熱量計算和低脂肪飲食來減肥的建議,實際上是基於薄弱的科學知識。它讓人們在減重過程中受了不少罪,而且感到十分挫敗。

「我們現在從研究中知道,糖和精製碳水化合物是肥胖和心臟病的真正原因,而不是脂肪,正如我們所談的那樣。」Hyman寫道。

「幸運的是,我們對脂肪的看法在轉變。過去五年來,科學證據表明,高脂肪飲食優於低脂膳食,無論在於減肥,還是在扭轉心臟病的每一個風險指標,包括膽固醇異常、糖尿病、高血壓、炎症等。」

脂肪細胞的「再訓練」

Ludwig建議用高質量的食物,包括健康脂肪來「再訓練你的脂肪細胞」,而不是用計算卡路里的方法。他說,使用正確的食物類型和組合(加上舒壓管理、獲得高質量的睡眠和參加愉悅身心的體力活動),脂肪細胞可以實現重新編程,以釋放其中儲存的熱量。

Ludwig指出,脂肪是我們飲食的重要組成部分,因為它使人很有飽足感。不吃脂肪會讓我們吃很多錯誤的食物來安撫我們的味蕾。事實上,堅果和奶酪等食物的中的健康脂肪並不會在脂肪細胞中儲存,除非它們與精製碳水化合物和糖一起食用。

Ludwig的方法旨在使用營養豐富的食物來降低胰島素水平、減少炎症,從而減少大多數減肥飲食中典型的飢餓反應。他建議吃各種營養豐富的食物,包括全脂奶製品如奶酪和酸奶,健康油脂如橄欖和鱷梨,蛋白質如豆腐、鮭魚和羊肉,以及堅果,蔬菜、水果、豆類,全穀物甚至黑巧克力。

他還建議,每個人對碳水化合物的敏感度不同,所以應該測試你的身體對它們的反應。首先戒掉所有澱粉、添加糖和人造甜味劑,兩個星期後加入適量的全穀物和澱粉類蔬菜。之後,根據你身體的處理能力,重新加入麵包、土豆和其它精製碳水化合物。當你吃白米飯時,如果你的體重立刻增加、感到身體困倦,那就嘗試用糙米或藜麥代替。

脂肪的救贖

近年來,一些政策制定者開始轉移了對脂肪的關注,因為糖代替脂肪成爲1號公敵。

2015年,美國疾病預防與健康促進辦公室在《膳食指南》中撤除了對膳食膽固醇的限制,並軟化了在脂肪限量方面的意見。雞蛋、蛋黃的好處再次被吹捧提倡。近年來,美國心臟協會和其它衛生機構已逐漸退出低脂飲食的觀點,並修訂了準則,更多地關注食物中的脂肪類型和整體飲食情況。

2015年英國醫學雜誌發表研究報告總結道,1977年和1983年向數百萬美國和英國公民發放的關於「脂肪飲食建議可以減少冠心病的發生率」,並沒有任何堅實的試驗證據支持,「這根本不應該公之於衆。」研究人員說。

2014年,支持抗糖、脂肪友好假說的前沿科學記者Taubes領導創立了一個非營利組織Nutrition Science Initiative(NuSI),以期解決這一研究問題。這一組織的目標是拋開我們對營養科學所知的一切,從頭開始。

在慷慨的資金資助下,NuSI將進行長期、獨立、目標宏大的研究──這些研究通常很少獲得研究資金──爲那些重要的營養學問題找到可靠答案。 Taubes還邀請了反對者──即低脂、卡路里方法的支持者來做研究。

雖然許多科學家和營養學家開始質疑所謂的飽和脂肪的危險性,但研究進展緩慢,政策制定者也在謹慎行事──以免造成另一個「大而肥胖」的營養學錯誤。

How Fat Became Public Enemy No. 1, and Why It’s Enjoying a Comeback

Author:Justina Reichel

For decades, we’ve been taught the same golden rule for maintaining a healthy weight: Simply burn more calories than you consume.

Therefore, being overweight, we’ve been told, is a personal flaw—a failure to follow the rules, or a result of weak willpower, laziness, or out-of-control gluttony.

But in recent years, a burgeoning number of scientists and journalists have come forward to suggest that the obesity crisis is caused by something far bigger than us: bad nutrition science, bad food policy, and chronic misinformation from the government and nutrition experts. In other words, it’s not (all) our fault.

In fact, the dietary advice we’ve been given for the past half century, they say, has created the perfect storm and near-ideal conditions for an obesity epidemic.

The Big, Fat Surprise: Fat Isn’t Bad for You

At the crux of issue, say advocates, is the demonization of fat that has been drilled into us since the 1970s.

It all started on Sept. 24, 1955, when then U.S. President Dwight Eisenhower suffered a moderate heart attack. Heart disease had been on the rise among middle-aged American men for years, and the president’s illness thrust the issue to the forefront.

As researchers scrambled to pinpoint a cause, charismatic and combative American physiologist Ancel Keys put forward a hypothesis: Saturated fat was the culprit, from foods like butter, red meat, eggs, and cheese. And it sounded completely logical: Eating fat makes you fat.

By the 1970s, Keys’s theory had taken hold among nutrition experts as the dominant paradigm, despite weak evidence and conflicting research that pointed to sugar, not fat, as the culprit.

As the war on fat took hold, dietary guidelines were changed and the food pyramid was introduced. Based on the idea that “a calorie is a calorie,” the pyramid advised minimizing all types of fat, which contain twice the calories of other major nutrients, such as carbohydrates. Instead, it recommended a diet centered around low-fat, high-carb foods (up to 11 servings of grain products like bread and pasta per day).

Meanwhile, food companies jumped on the marketing opportunity, stripping the fat out of products and promoting “healthy” options like low-fat cereal, crackers, cookies, and salad dressing. But they also knew that taking the fat out of food products meant losing flavor. The solution? Add sugar.

As saturated fat from foods like cheese and butter was put on the enemy list, they were replaced with products containing new “heart-healthy” fats, such as margarine made from chemically processed vegetable oils known as hydrogenated oils. (These oils, which contain trans fats, are now facing widespread boycotts as we learn more about the dangers they pose. In 2015, the FDA determined that trans fats are “not generally recognized as safe” and set a three-year time limit for their removal from all processed foods.)

“The idea that fat and saturated fat are unhealthy has been so ingrained in our national conversation for so long that we tend to think of it more as ‘common sense’ than a specific hypothesis,” writes journalist Nina Teicholz in her fat-exonerating book “The Big Fat Surprise: Why Butter, Meat and Cheese Belong in a Healthy Diet.”

“But, like any of our beliefs about the links between diet and disease, this one, too, began as an idea, proposed by a group of researchers, with its origin fixed at a moment in time.”

Although much of the Western world adopted this new low-fat, calorie-counting approach, often replacing dietary fat with refined carbohydrates, we continued to get fatter. And fatter. Since the 1970s, obesity has increased by 200 percent, and diseases related to obesity and diabetes are currently responsible for the deaths of two out of every three Americans.Fat is a crucial part of our diet because it so highly satiating. (Benjamin Chasteen/The Epoch Times)

All Calories Are Not Equal

The old adages of “calories in, calories out” and “eat less and move more” simply haven’t worked for most people in the long term. There are many benefits to exercising more, but weight loss often isn’t one of them, since exercising tends to make us hungrier. And it’s nearly impossible to out-exercise a bad diet; to burn off one doughnut, you would need to walk briskly for almost an hour.

It’s also very challenging to count the exact number of calories you consume every day and compare it accurately to the amount you burn—just a minor miscalculation could add up to several pounds a year. And even when you do successfully restrict calories, your body works against you, fighting back as it goes into “starvation mode.”

The calorie theory also suggests that eating a handful of almonds is the same as drinking a can of Coke, because the calorie count is similar. Or that low-fat cookies and no-fat, high-sugar yogurts are healthy options.

“New research has revealed the flaws in this way of thinking,” said Dr. David Ludwig, obesity expert and professor of pediatrics at Harvard Medical School, in his latest book “Always Hungry? Conquer Cravings, Retrain Your Fat Cells, and Lose Weight Permanently.”

“Recent studies show that highly processed carbohydrates adversely affect metabolism and body weight in ways that can’t be explained by their calorie content alone. Conversely, nuts, olive oil, and dark chocolate—some of the most calorie-dense foods in existence—appear to prevent obesity, diabetes, and heart disease.”

Ludwig, dubbed the “obesity warrior” by Time magazine, has joined other doctors such as Robert Lustig, David Perlmutter, and Mark Hyman, and journalists like Teicholz and Gary Taubes, to introduce a new theory: We don’t get fat because we eat fat or too many calories; we get fat because we eat sugar and processed carbohydrates, which are quickly digested and cause spikes in the hormone insulin. This reaction promotes fat storage in the body and sparks a vicious cycle of overeating as insulin spikes and plummets.

The new thinking goes, cut out the sugar and fast-digesting carbs (which your body treats as sugar), and you won’t get fat.

As anti-sugar crusader Lustig put it in his popular YouTube video “Sugar: The Bitter Truth”: “You are not what you eat—you are what you do with what you eat.”

The advice to focus on calorie counting and low-fat diets to lose weight was based on weak science and has caused people great suffering while thwarting their sincere efforts to be healthy, says Hyman in his book “Eat Fat, Get Thin.”

“We now know from the research that sugars and refined carbs are the true causes of obesity and heart disease—not fats, as we’ve been told,” he writes.

“Our views on fat, thankfully, are shifting. Over the last five years, the scientific evidence has been mounting that high-fat diets outperform low-fat diets for weight loss and for reversing every single indicator of heart disease risk, including abnormal cholesterol, diabetes, hypertension, inflammation, and more.”

Retraining Your Fat Cells

Instead of counting calories, Ludwig suggests “retraining your fat cells” with high-quality foods, including healthy fats. Using the right types and combinations of foods (as well as managing stress, and getting good-quality sleep and enjoyable physical activity), fat cells can be reprogrammed to release their pent-up calories, he says.

Fat is a crucial part of our diet, he notes, because it so highly satiating. Avoiding it makes us overeat the wrong foods to appease cravings. Contrary to what we’ve been told, healthy fats from foods like nuts and cheese do not get stored in fat cells—unless they’re eaten with refined carbs and sugar.

Ludwig’s approach aims at shutting down the starvation response typical to most weight-loss diets by using nourishing whole foods that lower insulin levels and reduce inflammation. He advises eating a wide variety of nutrient-dense foods including full-fat dairy products like cheese and yogurt, healthy oils such as olive and avocado, and proteins like tofu, salmon, and lamb, as well as nuts, vegetables, fruits, nuts, legumes, whole grains, and even dark chocolate.

He also suggests that each individual may have a different sensitivity to carbs, so it’s a good idea to test your body’s reactions to them. Start by cutting out all starches, added sugars, and artificial sweeteners for two weeks. Then add back moderate amounts of whole grains and starchy vegetables. After that, reintroduce bread, potatoes, and other processed carbs, depending on your body’s ability to handle them. Do you instantly gain weight and feel sluggish when you eat white rice? Try brown rice or quinoa instead.

Sheet-pan salmon, a three-in-one meal. (Caroline Chambers)

Fat’s Redemption

In recent years, some policymakers have started to back away from the focus on fat, as sugar takes its place as public enemy No. 1.

In 2015, the U.S. Office of Disease Prevention and Health Promotion removed limits on dietary cholesterol in its Dietary Guidelines and softened its view on reducing fat in its advice. Eggs, yolks included, were again touted as good for us. In recent years, the American Heart Association and other health organizations have backed away from the low-fat message and revised guidelines to focus more on the types of fat in foods and on the diet as a whole.

A 2015 study published by the British Medical Journal concluded that dietary advice on fat consumptionissued to millions of U.S. and U.K. citizens in 1977 and 1983 to cut coronary heart disease incidencelacked any solid trial evidence to back it up and “should not have been introduced,” researchers concluded.

A nonprofit led by Taubes, a science journalist at the forefront of the anti-sugar, fat-friendly hypothesis, was created in 2014 to address this research problem. The aim of the organization, Nutrition Science Initiative (NuSI), is to throw out everything we know about nutrition science and start from scratch.

With the help of generous funding, NuSI aims to conduct the type of long-term, independent, and ambitious studies that nutrition research rarely gets the money for to find reliable answers to our big nutrition questions. Taubes also invited naysayers—proponents of the low-fat, calorie balance approach—to do some of the research.

While many scientists and nutritionists start questioning the supposed dangers of saturated fat, the progress is slow and policymakers are treading carefully—lest they make another big, fat mistake.