Keto, a diet that emphasizes cutting down carbs and sugar, has been used for some 50 years as a way for folks to lose weight fast.
Significant weight loss could help prevent cancer. Recent research even showed keto might help treat it too, by starving existing cancer cells of the sugar they need.
But now, a new study suggests keto diets might not always be a cancer hero. In fact, while curbing cancer growth in one area of the GI tract, keto could encourage it in another.
The key to keytones
Popularized for weight loss in the 1970s, the keto diet has people avoiding bread, pasta, sugar and starchy vegetables like potatoes and corn. Atkins is a similar low carb diet.
Keto works by putting the body into a fasting state, making it burn fat for energy rather than sugar. This process is called ketosis, and it releases ketones into the blood stream to energize the body.
A 2022 study showed that it was these ketones that could slow colorectal cancer from spreading. A ketone called BHB told cells to stop dividing, researchers said.
“When we treated [colorectal cancer] cells with BHB, they didn’t die, but they seemed to start sleeping,” said author Maayan Levy.
Colorectal cancer is the only major cancer rising in people under 50, and as many as 75% of young patients are diagnosed at an advanced stage. It is the deadliest cancer for people under 50.
But the new study out of MIT suggests what works in the colon may not work elsewhere in the GI tract — and keytones may not be the major player we thought.
The small intestine
Though the diet worked to prevent cancer in the colon, the last stage of digestion, MIT researchers were surprised to see it had the opposite effect in the small intestine in mice.
Keto made tumors more likely to appear in this region of the mice’s GI tract.
“Ketogenic diets have distinct effects on different tissues even within the gastrointestinal tract,” says Omer Yilmaz, senior author on the paper. “We need to be very careful in generalizing the effects that these diets can have, because what might be beneficial for one tissue may be detrimental for another tissue.”
The diet did keep the mice trim, but tumors were appearing at similar rates to what was seen in obese mice.
Why was this happening? Researchers believe keto’s effects both in the small and large intestines aren’t related to ketones, as previously thought. They believe it’s all about stem cells.
They found that cells burning fat (from ketosis) start a chain reaction which leads to stem cells multiplying rapidly, increasing the chance they go out of control and become cancer.
Stem cells can be good — they help the small intestine repair itself — “but the downside is that having more active stem cells can lead to tumor formation,” Yilmaz says.
In the large intestine, Yilmaz’s team say that keytones were “essentially metabolic bystanders” compared to what stem cells were up to.
Researchers call for further study to find out exactly why two neighboring GI tract organs react so differently to a keto diet.
This is important because though small intestine cancer is rare — affecting about 14,400 people in the US annually — cases have doubled over the last 40 years.
