“如果它聽起來太美好，簡直不像是真的，那很可能就不是真的。”人工增甜劑的例子就屬于這種情況。

一份新的研究發現，沒有證據顯示人工增甜劑能幫助人們減肥。相反，這份報告分析了對低卡路里和無卡路里增甜劑的37份研究，得出的結論是這些糖類替代品會導致體重增加，食用者未來還可能會有健康問題。

這份報告發表于《加拿大醫學協會期刊》，給在食品和飲料中采用人工增甜劑（而不是糖）對健康有益的想法潑了盆冷水。這是條重要的消息：自20世紀90年代以來，由于美國人對糖類越來越警惕，低卡路里的增甜劑在美國的使用量迅速攀升。

綜述所分析的研究中，有7項是隨機調查，30項是觀察調查（也就是對研究對象的習慣和健康狀況進行了一段時間的觀察）。隨機調查選擇的對象總計1,000名，其中大部分都試圖減肥，然而研究人員沒有找到人工增甜劑導致體重減輕的證據。

觀察調查涉及的對象總計約40.6萬人。研究人員發現人工增甜劑與身體質量指數的小幅增加（以及罹患II型糖尿病的概率小幅增加）呈現相關。當然，值得指出的是，這些研究是觀察調查，因此沒有實驗對照組，無從判定人工增甜劑是否確實導致了BMI的增加和糖尿病患病風險的增加。不過它對低卡路里的增甜劑有助于緩解普遍肥胖的想法提出了進一步的質疑。

盡管綜述針對的是人工制造的糖類替代品（例如阿斯巴甜和糖精），但它也對“天然的”糖類替代品表示了懷疑。例如從植物中提取的甜菊糖，以及常常被宣稱能神奇地產生甜味卻不會對健康產生負面影響的赤蘚糖醇。

對于人工增甜劑這樣的替代品會給身體帶來哪些長期影響，我們所知甚少，這多少會引發人們的擔憂。研究人員認為，它們會影響腸道細菌，以及身體處理糖類的能力，盡管這些說法尚未得到證實。

人工增甜劑還會影響習慣的養成。許多利用糖類替代品的公司都宣稱他們的垃圾食品是“健康”版的。其中最著名的品牌之一就是低卡路里冰淇淋公司Halo Top。該公司一品脫巧克力冰淇淋只有280卡路里，而一品脫哈根達斯巧克力冰淇淋的熱量大約是1,040卡路里。之所以有這么大的差異，是因為Halo Top在配方中采用了甜菊糖和赤蘚糖醇，以減少糖類的使用。

Halo的廣告中透露的強烈意思是他們的產品對你的健康很好——實際上，實在是太好了，以至于他們甚至表示一口氣吃掉一品脫冰淇淋沒什么問題，甚至鼓勵你這么做。（公司的網站寫著：“拿好你的碗，你會想要吃掉這整整一品脫。”而其蓋子上還寫著：“吃到底再停下。”）Halo Top并對應要求對此做出評論。

營養學家擔心這類信息無益于幫助減肥者，而是在鼓勵他們培養不健康的飲食習慣，這最終會導致增肥。哥倫比亞大學人體營養學院的副主任莎倫·阿卡巴斯表示，Halo這樣的產品一方面“可以被視作減輕危害的產品，另一方面，公司又因為‘健康Halo’的形象而受益——這里不是雙關。人們忘記了這些產品很大意義上仍然是垃圾食品。它們混淆了垃圾食品與否的界限。”

紐約大學營養、食品研究和公共衛生領域的教授馬里昂·奈斯德對此表示同意。她在給《財富》的郵件中表示：“更好的辦法可能還是在食品中少加點糖。”

這份關于人工增甜劑的研究是一個很好（也許也是令人沮喪）的提醒：想減肥，幾乎沒有捷徑可走。（財富中文網）

譯者：嚴匡正

File this one under "if it sounds too good to be true, it probably is."

A new review found no evidence that artificial sweeteners actually help people lose weight. Instead the report, which analyzed 37 studies on low and no-calorie sweeteners, linked these sugar replacements to weight gain and future health problems.

Published in Canadian Medical Association Journal, the report puts a damper on the idea that switching to food and beverages sweetened with artificial sweeteners (rather than sugar) has any major health benefits. This is important news: Since the 1990s, the use of low-calorie sweeteners in the U.S. has skyrocketed as Americans have grown increasingly wary of sugar.

Of the reviewed studies, seven were randomized and 30 were observational (meaning participants’ habits and health were tracked over a set period of time). After studying the randomized trials, which consisted of a total of 1,000 people, most of whom were trying to lose weight, the researchers found no evidence that artificial sweeteners led to weight loss.

From the observational studies, which consisted of around 406,000 participants in total, the researchers found a link between artificial sweeteners and a small increase in BMI (plus a slight increase in the likelihood of developing Type 2 diabetes). It’s important to note, of course, that because these studies were observational, meaning there was no control group, it’s impossible to determine whether artificial sweeteners actually caused the uptick in BMI or diabetes risk. But it further questions the idea that low-calorie sweeteners are the answer to the obesity epidemic.

While the review focused on artificial sugar substitutes (such as aspartame and saccharin), it casts doubt on “natural” sugar replacements like stevia—which is derived from a plant—and the sugar alcohol erythritol, which are often advertised as magical replacements able to recreate sugar's taste without recreating its detrimental consequences on health.

As with artificial sweeteners, some of this concern arises from how little we know about these replacements’ long-term effects on the body. Researchers have suggested they could interfere with gut bacteria and the body’s ability to process sugar, although these theories are unconfirmed.

It also has to do with habit building. A number of companies that use sugar replacements market themselves as “healthy” versions of junk food. One of the most prominent is the low-calorie ice cream brand Halo Top. A pint of its chocolate ice cream contains 280 calories, versus the roughly 1,040 in a pint of chocolate Haagen Daz. To achieve this discrepancy, Halo Top uses both stevia and erythritol to cut back on the amount of sugar in its recipe.

Halo’s advertising leans heavily on the idea that its products are good for you—so good for you, in fact, that it’s fine, encouraged even, to eat an entire pint in one sitting. (“Save the bowl, you’re going to want the whole pint,” its website reads, while Halo pint lids come emblazoned with the command to “stop when you get to the bottom.”) Halo Top did not respond to a request for comment.

Nutritionists worry that this type of messaging, instead of helping those trying to lose weight, encourages unhealthy eating habits that lead to weight gain. Products like Halo, on one hand “can be seen as a form of harm reduction,” says Sharon Akabas, the associate director of the Institute of Human Nutrition at Columbia University. “On the other hand they benefit from being a 'healthy halo' -- no pun intended. People forget they are still mostly a junk food. Products like these blur boundaries.”

Marion Nestle, a professor of nutrition, food studies, and public health at New York University, concurs. “A better approach might be smaller portions of the real stuff," she tells Fortune in an email.

The review on artificial sweetener serves as a good (if frustrating) reminder that when it comes to weight loss, there are few, if any, shortcuts.