2014年10月5日 星期日

人工甜味劑可能影響人體糖代謝

人工甜味劑可能影響人體糖代謝

科研人員通報,人工甜味劑或許會干擾人體控制血糖的能力,導致可視為糖尿病前兆的代謝變化。
在討論這一發現的新聞發佈會上,以色列魏茨曼科學研究學院(Weizmann Institute of Science)的免疫學家埃蘭·伊萊納夫博士(Eran Elinav)表示,這「恰好是我們」用甜味劑代替糖時「通常希望避免的那種情況」。
  • 檢視大圖甜味劑會改變消化系統的微生物菌群。
    Weizmann Institute of Science
    甜味劑會改變消化系統的微生物菌群。
科學家們在以小鼠為主的實驗對象身上進行了大量實驗,以支持他們的結論:甜味劑會改變消化系統中的微生物菌群。
研究人員指出,不同的菌群構成會改變葡萄糖的代謝,導致餐後血糖濃度升得更高、回落的速度也更慢。
伊萊納夫的以色列合作者中,包括魏茨曼學院的計算機科學與應用數學教授埃蘭·賽加爾(Eran Segal)。他們的這項發現發表在周三出版的《自然》雜誌(Nature)上。
芝加哥大學(University of Chicago)的病理學教授凱瑟琳·R·納格勒(Cathryn R. Nagler)沒有參與這項研究,不過在《自然》雜誌上進行了相關評論,稱他們的研究結果「非常有說服力」。
她指出,包括肥胖症和糖尿病在內的許多癥狀已被認為與微生物菌群的變化有關。「本研究表明,我們應該退後一步,重新評估我們對人工甜味劑的廣泛使用,」她說。
此前對人工甜味劑的健康影響進行的多項研究,得出了相互矛盾、令人困惑的結論。一些研究認為,甜味劑與減重有關;另一些則正好相反,發現飲用健怡汽水的人實際更重。
還有一些研究的結論是,人工甜味劑與糖尿病正相關。不過這些結論並不完全可信:那些放棄糖,而消費甜味劑產品的人可能本已超重,易於罹患糖尿病。
儘管承認得出廣泛結論或決定性的結論還為時尚早,但伊萊納夫表示,他已經對自身行為做出了改變。
「我喝很多很多的咖啡,大量使用甜味劑,和很多人一樣,以為它們起碼不會傷害我的身體,說不定還有好處,」他說。「基於我們的研究得出的意外結果,我個人選擇不再使用甜味劑。」
「我並不認為,我們提出的證據足以修改目前的飲食建議,」他接著說。「但我希望,這將引發一場良好的討論。」
在初步實驗中,科學家們把糖精(粉色包裝的纖而樂[Sweet』N Low]的甜味劑)、三氯蔗糖(黃色包裝的善品糖[Splenda]的甜味劑)或阿斯巴甜(藍色包裝的怡口[Equal]的甜味劑)添加到飲用水中,讓10周大的小鼠攝入。其他小鼠則喝白水,或者添加了葡萄糖或普通食糖的水。一周之後,飲用白水或糖水的小鼠變化不大,但攝入人工甜味劑的那組小鼠明顯出現了葡萄糖耐受不良。
葡萄糖耐受不良表明身體處理大量糖分的能力降低,可能會導致更加嚴重的疾病,比如代謝綜合征和2型糖尿病。
當研究人員對小鼠使用抗生素,殺死其消化系統中的很多細菌之後,它們的葡萄糖耐受不良問題就消失了。
目前,科學家尚無法解釋甜味劑是如何影響這些細菌的,以及為什麼在葡萄糖代謝過程中,糖精、阿斯巴甜和三氯蔗糖這三種不同的分子導致了類似的變化。
科學家們假設葡萄糖代謝中的變化是由細菌的變化引起的,為了進一步檢驗這個假設,他們開展了另外一系列只針對糖精的實驗。科學家們從攝入了糖精水的小鼠身上取出腸道細菌,注入到從未接觸過任何糖精的小鼠體內。隨後這些小鼠也出現了葡萄糖耐受不良。DNA測序表明,在攝入糖精的小鼠的腸道中,糖精明顯改變了細菌種類的組合。
接下來,研究人員開始追蹤營養和腸道細菌對人體長期健康的影響。這項研究有381例非糖尿病患者參加,研究人員發現,任何一種人工甜味劑的攝入,都和葡萄糖耐受不良體征之間存在着相關性。此外,有沒有攝入人工甜味,腸道細菌會不一樣。
最後,研究人員招募了七名通常不使用人工甜味劑的志願者,並在六天時間中,讓他們攝入了美國食品與藥品管理局(Food and Drug Administration,簡稱FDA)建議的糖精最大攝入量。結果七人中有四人的血糖值出現了與小鼠類似的變化。
此外,當他們把人類受試者的細菌注入到小鼠的腸道中後,小鼠再次出現了葡萄糖耐受不良,這表明該效應在小鼠和人類中是相同的。
「我認為這個實驗很令人信服,」納格勒博士說。
有趣的是——「讓我們覺得既震驚又有趣」,西格爾博士說——出現了這種效應的人,其腸道細菌不同於沒有經受它的人。這表明,人工甜味劑的任何效應都不是放之四海而皆準的。這也表明,益生菌——含有活細菌的藥品——可用於改變腸道細菌群,以逆轉葡萄糖耐受不良。
哈佛大學公共衛生學院(Harvard School of Public Health) 的營養和免疫學教授弗蘭克•胡(Frank Hu)博士沒有參與這項研究,他稱該研究很有趣,但還遠遠不能就此做出結論,因為受試者人數不足,他說,「我認為這項人體研究的正確性存在問題。」
研究人員表示,未來的項目會對阿斯巴甜、三氯蔗,以及甜葉菊等其他甜味劑進行詳細研究。
翻譯:黃錚

Artificial Sweeteners May Disrupt Body’s Blood Sugar Controls

That is “the very same condition that we often aim to prevent” by consuming sweeteners instead of sugar, said Dr. Eran Elinav, an immunologist at the Weizmann Institute of Science in Israel, at a news conference to discuss the findings.
The scientists performed a multitude of experiments, mostly on mice, to back up their assertion that the sweeteners alter the microbiome, the population of bacteria that is in the digestive system.
The different mix of microbes, the researchers contend, changes the metabolism of glucose, causing levels to rise higher after eating and to decline more slowly than they otherwise would.
The findings by Dr. Elinav and his collaborators in Israel, including Eran Segal, a professor of computer science and applied mathematics at Weizmann, are being published Wednesday by the journal Nature.
Cathryn R. Nagler, a professor of pathology at the University of Chicago who was not involved with the research but did write an accompanying commentary in Nature, called the results “very compelling.”
She noted that many conditions, including obesity and diabetes, had been linked to changes in the microbiome. “What the study suggests,” she said, “is we should step back and reassess our extensive use of artificial sweeteners.”
Previous studies on the health effects of artificial sweeteners have come to conflicting and confusing findings. Some found that they were associated with weight loss; others found the exact opposite, that people who drank diet soda actually weighed more.
Some found a correlation between artificial sweeteners and diabetes, but those findings were not entirely convincing: Those who switch to the products may already be overweight and prone to the disease.
While acknowledging that it is too early for broad or definitive conclusions, Dr. Elinav said he had already changed his own behavior.
“I’ve consumed very large amounts of coffee, and extensively used sweeteners, thinking like many other people that they are at least not harmful to me and perhaps even beneficial,” he said. “Given the surprising results that we got in our study, I made a personal preference to stop using them.
“We don’t think the body of evidence that we present in humans is sufficient to change the current recommendations,” he continued. “But I would hope it would provoke a healthy discussion.”
In the initial set of experiments, the scientists added saccharin (the sweetener in the pink packets of Sweet’N Low), sucralose (the yellow packets of Splenda) or aspartame (the blue packets of Equal) to the drinking water of 10-week-old mice. Other mice drank plain water or water supplemented with glucose or with ordinary table sugar. After a week, there was little change in the mice who drank water or sugar water, but the group getting artificial sweeteners developed marked intolerance to glucose.
Glucose intolerance, in which the body is less able to cope with large amounts of sugar, can lead to more serious illnesses like metabolic syndrome and Type 2 diabetes.
When the researchers treated the mice with antibiotics, killing much of the bacteria in the digestive system, the glucose intolerance went away.
At present, the scientists cannot explain how the sweeteners affect the bacteria or why the three different molecules of saccharin, aspartame and sucralose result in similar changes in the glucose metabolism.
To further test their hypothesis that the change in glucose metabolism was caused by a change in bacteria, they performed another series of experiments, this time focusing just on saccharin. They took intestinal bacteria from mice who had drank saccharin-laced water and injected them in mice that had never been exposed any saccharin. Those mice developed the same glucose intolerance. And DNA sequencing showed that saccharin had markedly changed the variety of bacteria in the guts of the mice that consumed it.
Next, the researchers turned to a study they were conducting to track the effects of nutrition and gut bacteria on people’s long-term health. For 381 nondiabetic participants in the study, the researchers found a correlation between the reported use of any kind of artificial sweeteners and signs of glucose intolerance. In addition, the gut bacteria of those who used artificial sweeteners were different from those who did not.
Finally, they recruited seven volunteers who normally did not use artificial sweeteners and over six days gave them the maximum amount of saccharin recommended by the United States Food and Drug Administration. In four of the seven, blood-sugar levels were disrupted in the same way as in mice.
Further, when they injected the human participants’ bacteria into the intestines of mice, the animals again developed glucose intolerance, suggesting that effect was the same in both mice and humans.
“That experiment is compelling to me,” Dr. Nagler said.
Intriguingly — “superstriking and interesting to us,” Dr. Segal said — the intestinal bacteria of the people who did experience effects were different from those who did not. This suggests that any effects of artificial sweeteners are not universal. It also suggests probiotics — medicines consisting of live bacteria — could be used to shift gut bacteria to a population that reversed the glucose intolerance.
Dr. Frank Hu, a professor of nutrition and immunology at the Harvard School of Public Health who did not take part in the study, called it interesting but far from conclusive and added that given the number of participants, “I think the validity of the human study is questionable.”
The researchers said future research would examine aspartame and sucralose in detail as well as other alternative sweeteners like stevia.

沒有留言: