Ketones might not be the hero everyone thought.
A new study published in Nature throws a wrench in the popular theory that the ketogenic diet protects against cancer simply because of the ketone bodies it produces. In fact, the results suggest the mechanism is far more complex—and potentially dangerous for certain parts of your gut.
Originally designed for epilepsy, keto has morphed into a mainstream weight loss strategy. Even some researchers looked toward it for Alzheimer’s or as a cancer fighter. But here’s the catch. We never really knew how it affected the entire digestive tract. Only pieces.
Opposite Outcomes
Now we have a bigger piece of the puzzle. It’s contradictory.
MIT researchers, led by Omer Yilmaz and Jessica Shay, fed genetically predisposed mice three types of food: a ketogenic diet, a normal control, or a standard obesity-inducing high-fat mix. The results didn’t match the headlines.
In the colon, keto still suppressed tumors. This aligns with past hopes. But in the small intestine? The diet accelerated tumor growth.
Surprisingly, neither increasing nor eliminating ketone formation changed whether the tumors grew or not.
That was the shock. Not just that the outcomes differed by location, but that ketone production seemed irrelevant to either. Mice on the keto diet got lean, yes, but their small intestine tumors grew at rates comparable to mice fed a fattening obesity diet.
So if not ketones, what?
It’s About The Fat
For years, scientists fixated on beta-hydroxybutyrate, or BHB. They thought these molecules were the key. A 2022 study even leaned hard into the idea that BHB protected the colon from cancer.
The new MIT findings say no.
It wasn’t the ketones. It was how intestinal cells burned the fat itself.
When those cells underwent fatty acid oxidation, they activated proteins known as PPARs. These proteins told stem cells in the lining of the gut to divide faster.
More stem cells mean better repair after injury. That sounds good, right?
Except it also means more opportunities for mutations. More division increases the statistical chance that one cell goes wrong and becomes cancerous.
Yilmaz noted that this explains the risk. More active stem cells help you heal, but they also fuel tumors if you have genetic predispositions.
Distinguishing Diet From Supplement
This distinction matters. Big time.
Jessica Shay, co-first author on the paper, pointed out that diet and metabolism get conflated all the time. They aren’t the same thing. The protective or harmful effects came from the high dietary fat content driving fatty acid metabolism. Not the ketosis. Not the supplements.
This suggests that buying ketone esters or exogenous ketones likely won’t mimic the cancer-fighting benefits people hope for, nor will it replicate the risks seen in the mouse study. Those biological drivers were missing entirely.
Are you better off popping ketone pills if you eat standard fare? Based on this? Probably not. The effect came from how the tissue handled the fat intake itself.
The Unknown Variable
There’s still a gaping hole in the logic. Why the difference?
The colon and the small intestine are neighbors. They process the same meal. Yet one got suppressed while the other accelerated growth under the exact same ketogenic regime.
Yilmaz doesn’t have an answer yet. The team is actively working on it. It remains a black box.
These results also carry weighty caveats. The mice were genetically wired for tumors, similar to humans with familial adenomatous polyposis—a rare condition. We don’t know if healthy human intestines react the same way to fat oxidation via PPAR activation.
But the takeaway isn’t just caution. It’s a reminder that simple dietary labels often hide complex biology. We wanted a magic bullet in fat and ketones.
We got a paradox instead.
Which leaves us with the usual question: what should you eat tomorrow? The data is incomplete, but it forces a rethink.
