A reason to eat carbs

A high-fat, low-carbohydrate diet can help some people lose weight, and some research has shown that it may protect against colon cancer. But a new study suggests that such a ketogenic diet may also increase the risk of cancer in the small intestine.

高脂肪、低碳水化合物的饮食可以帮助一些人减肥，一些研究也表明它可能有助于预防结肠癌。但一项新的研究表明，这种生酮饮食也可能会增加小肠患癌的风险。

This type of diet forces the body to burn fatty acids instead of carbohydrates for fuel, producing by-products called ketone bodies. One of these, BHB, was thought to be responsible for the protective effect observed against colon cancer.

这种饮食方式迫使身体燃烧脂肪酸而非碳水化合物来获取能量，从而产生被称为酮体的副产品。其中一种名为 BHB 的物质曾被认为是在结肠癌预防中观察到的保护作用的来源。

Omer Yilmaz, director of the MIT Stem Cell Initiative, worked with colleagues including MIT postdocs Jessica Shay and Fangtao Chi to investigate whether the effects were similar in the small intestine. But instead, they found that mice on a ketogenic diet were more likely to develop tumors in that part of the gastrointestinal system than those on a control diet were.

麻省理工学院干细胞计划主任 Omer Yilmaz 与包括博士后 Jessica Shay 和 Fangtao Chi 在内的同事合作，研究了这种影响在小肠中是否相似。然而，他们发现，与对照组相比，采用生酮饮食的小鼠在消化系统的这一部分更容易长出肿瘤。

Additional studies revealed that this tumor growth was driven by the way intestinal cells burn dietary fat for energy—a metabolic pathway called fatty acid oxidation. This pathway activates proteins that signal stem cells to multiply more rapidly.

进一步的研究表明，这种肿瘤生长是由肠道细胞燃烧膳食脂肪以获取能量的方式驱动的，这是一种被称为脂肪酸氧化的代谢途径。该途径会激活蛋白质，向干细胞发出信号，使其更快速地增殖。

“Having more stem cells means that when you injure the small intestine, it can repair itself better, but the downside is that having more active stem cells can lead to tumor formation,” Yilmaz says. Though the researchers confirmed that a ketogenic diet suppressed the development of colon tumors, their findings suggest that ketone bodies are not involved.

Yilmaz 说：“拥有更多的干细胞意味着当你损伤小肠时，它能更好地自我修复，但缺点是拥有更多活跃的干细胞可能会导致肿瘤形成。”尽管研究人员证实生酮饮食抑制了结肠肿瘤的发展，但他们的发现表明酮体并不参与其中。

“These molecules are essentially metabolic bystanders,” Yilmaz says. One implication is that commercial ketone supplements probably do little to either help or harm people who take them. But the deeper issue is “why the same diet has opposite consequences in two adjacent parts of the gut,” Chi says. “That is what we are working to understand next.”

Yilmaz 说：“这些分子本质上是代谢的旁观者。”一个暗示是，商业化的酮补充剂对于服用它们的人来说，可能既没有多大帮助，也没有多大危害。但更深层的问题是，“为什么同样的饮食在肠道的两个相邻部分会产生相反的结果，”Chi 说，“这就是我们接下来要努力去理解的。”

Whatever they discover, as Yilmaz says, “the message here is that we need to be very careful in generalizing the effects that these diets can have.”

正如 Yilmaz 所说，无论他们发现什么，“这里传达的信息是，我们在概括这些饮食可能产生的影响时需要非常谨慎。”