Mice fed a ketogenic diet died more quickly than those on a standard control diet in a study published this month – and the culprit wasn’t what most researchers expected. For years, the prevailing theory held that ketone bodies, particularly a molecule called beta-hydroxybutyrate (BHB), were the key bioactive players behind whatever cancer-protective effects the keto diet appeared to offer. The new findings from MIT suggest those molecules are essentially bystanders. Dietary fat itself is the driver.
A high-fat, low-carbohydrate ketogenic diet, while popular for weight loss, may increase the risk of small intestinal tumors, according to research published in Nature by researchers at MIT. The study, titled “Ketogenic diet mediates intestinal tumorigenesis through lipids not ketones,” arrives at a moment when millions of people are following high-fat eating regimens for health reasons ranging from weight control to blood sugar management – and when keto diet cancer research had largely been trending in a hopeful direction.
Ketogenic diets were originally developed in the 1920s as a way to treat epilepsy. The diet comprises a high percentage of fat, a low percentage of carbohydrates, and normal or reduced amounts of protein. This forces the body to burn fatty acids for energy in place of carbohydrates such as glucose. Burning these lipids produces ketone bodies – primarily beta-hydroxybutyrate (BHB) and acetoacetate – as byproducts of fatty acid metabolism. That metabolic shift has been hailed as the mechanism behind many of keto’s purported benefits. The MIT study challenges whether ketone bodies deserve anywhere near that credit.
The MIT Study: Design and Key Findings
The MIT team designed their study to explore whether ketogenic diets might have a protective effect in the small intestine, similar to findings previously reported for the colon. They fed mice genetically predisposed to developing intestinal cancer either a ketogenic diet, a control diet, or a high-fat, high-calorie diet. They found that mice on a ketogenic diet were more likely to develop tumors of the small intestine than those on a control diet.
While they did not become obese, mice on the ketogenic diet developed tumors at rates similar to or even higher than those of mice on an obesogenic high-fat, high-calorie diet. That comparison is clinically significant: the ketogenic group maintained a lean body weight, which is typically associated with lower cancer risk. Their tumor burden matched or exceeded that of obese animals – a finding the researchers had not anticipated.
Additional studies revealed that ketone bodies did not play a role in tumor development. Surprisingly, the same ketogenic diet that promoted tumors in the small intestine had the opposite effect in the colon. The researchers found, similar to the earlier study back in 2022, that a ketogenic diet suppressed the development of colon tumors. The same diet. The same animals. Opposite outcomes, separated by only a few inches of anatomy.
Omer Yilmaz, PhD, director of the MIT Stem Cell Initiative, an associate professor of biology at MIT, and a member of MIT’s Koch Institute for Integrative Cancer Research, captured the core implication: “Ketogenic diets have distinct effects on different tissues even within the gastrointestinal tract. I think the message here is that 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 Mechanism: Fat Metabolism, Not Ketones
“Given how much attention has been paid to ketone bodies like BHB, both as a commercial health trend and in recent high-profile studies suggesting BHB suppresses colon cancer, we fully expected them to be the direct drivers. Instead, our experiments in genetically engineered mice revealed that these molecules are essentially metabolic bystanders. The real surprise is that tumor acceleration is driven entirely by how stem cells process and burn the heavy influx of dietary fat itself,” Yilmaz said.
The mechanistic pathway works like this: tumor growth was driven by how intestinal cells burn dietary fat for energy – a metabolic pathway called fatty acid oxidation. This pathway activates a family of proteins called PPARs (peroxisome proliferator-activated receptors), which signal stem cells to multiply more rapidly, increasing the chance that some become cancerous.
This stem cell proliferation can be beneficial in certain situations, such as when the intestinal lining needs to be repaired after illness or injury. However, too much proliferation can tip cells toward becoming cancerous. As Yilmaz explained in a statement covered by EurekAlert!: “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.”
MIT molecular biologist and co-first author Fangtao Chi made the mechanistic split explicit. The team found that “neither increasing nor eliminating ketone production altered intestinal tumor growth. Instead, we found that its tumor-promoting effects in the small intestine were driven by the metabolism of dietary fat rather than by ketone bodies.”
The Nature paper confirmed this in molecular detail. Combined intestinal loss of PPARα/δ/γ attenuates ketogenic diet-driven intestinal stem cell expansion, proliferation, and clonogenicity, whereas inhibition of downstream fatty acid oxidation through CPT1A loss limits adenoma formation specifically under these dietary conditions. In plain terms: blocking the fat-burning proteins eliminated the tumor-promoting effect, confirming fat metabolism as the causal driver.
What Was Already Known About Keto and Cancer
The new MIT findings do not emerge from a vacuum. The research team was directly following up on a 2022 study in Nature that had shown a very different picture – one where BHB appeared protective against colorectal cancer. That 2022 Nature study, from researchers at the University of Pennsylvania, suggested that ketogenic diets have a protective effect against colon cancer and that BHB – the most abundant ketone body – is responsible for this effect.
That 2022 research established a specific mechanistic pathway: BHB acts through the surface receptor HCAR2 and induces the transcriptional regulator HOPX, which alters gene expression and inhibits cell proliferation in colonic tissue. The MIT study does not contradict those colon cancer findings – it recontextualizes them. The same colon protection holds. However, the new findings suggest that ketone bodies are not responsible for this protective effect. Both the protective effect in the colon and the tumor-promoting effect in the small intestine now appear to run through fat metabolism, not ketone production. This has meaningful consequences for how researchers and consumers interpret keto’s cancer-related claims.
A Genuinely Paradoxical Biology
The most striking aspect of the MIT findings is the tissue-specificity. Two sections of the same digestive tract, exposed to the same diet, at the same time, in the same animal, produce opposite tumor outcomes. The ketogenic diet does not affect the entire digestive tract uniformly. While the colon saw a reduction in tumor development, the small intestine showed an increased risk of tumor formation in mice genetically predisposed to cancer.
Yilmaz acknowledged this as an open scientific question. “The team is now trying to understand why the same diet has such different effects in two neighboring parts of the intestine. ‘We don’t know why they’re responding differently,’ said Yilmaz. ‘That’s the question we’re working on next.'”
The study’s relevance to humans is also not yet fully established. The experiments were conducted in a mouse model genetically predisposed to developing intestinal tumors. The closest human equivalent is familial adenomatous polyposis – a rare inherited condition that greatly increases the risk of developing intestinal tumors. The researchers say more work is needed to determine whether the same mechanisms operate in people.
Because the diet’s effects – both the tumor acceleration in the small intestine and the protection in the colon – are driven entirely by fat metabolism rather than the ketones themselves, commercial ketone supplements or drinks would not be expected to mimic either the risks or the benefits discovered in this study. This may be especially relevant given that small intestinal tumors have been rising in incidence in recent decades, with the greatest impact on patients with inherited conditions that predispose them to intestinal cancer, such as familial adenomatous polyposis.
The Broader Context: Keto’s Established Applications
None of this erases what keto has demonstrated in other clinical contexts. The diet has over a century of documented use in epilepsy management, with a 2025 article in Nutrients noting it has been used as a treatment in epilepsy for over 100 years. There is also a robust evidence base for its metabolic effects:A 2020 meta-analysis in Nutrients reviewing 14 randomized controlled trials found that ketogenic diets can support weight loss and improve measures of blood sugar control, particularly in people with obesity and type 2 diabetes, compared with lower-fat diets.
The Alzheimer’s research is also active and growing. A 2025 study in Communications Medicine found that consuming a modified Mediterranean ketogenic diet reverses the peripheral lipid signature of Alzheimer’s disease – suggesting the diet alters metabolic markers linked to neurodegeneration. A separate 2025 study in Frontiers in Aging Neuroscience found that the APOE4 gene variant – the strongest genetic risk factor for Alzheimer’s disease, increasing risk approximately fourfold – may influence how the brain responds to a ketogenic diet, with mice carrying the variant showing improved memory compared to those on high-carbohydrate diets.
These applications, which are in medically supervised contexts and specific patient populations, exist in a different category from the broad consumer use of keto for general wellness or cancer prevention. The MIT findings don’t negate the epilepsy or metabolic data. They do signal that the diet’s cancer-related effects are far more tissue-specific and mechanism-dependent than previously understood.
Read More: RFK Jr. Said Keto Can Cure Schizophrenia. Here’s What Experts Actually Found
The Bottom Line
The practical implications of this research depend heavily on who you are. For the general healthy adult following keto for weight loss or blood sugar management, the MIT study does not establish any direct human cancer risk. The experiments were conducted in mice with a genetic predisposition to intestinal cancer. Translating those findings to people who don’t carry that predisposition requires human trials that have not yet been conducted. Yilmaz’s team has been explicit on this point: more work is needed before any clinical recommendations can be made.
For people with familial adenomatous polyposis (FAP) or other hereditary conditions that elevate intestinal cancer risk, the findings are a direct signal to discuss any high-fat dietary approach with a specialist before proceeding. The impact of ketogenic diets on intestinal cancer risk is particularly relevant for patients with FAP, who already face a high risk of small-intestinal tumors. That conversation matters now – not after waiting for human trial data.
The finding also clarifies a widely misunderstood commercial claim. Because the tumor-promoting effects were linked to fat metabolism rather than ketone bodies themselves, simply increasing ketone levels through supplementation may not carry the same biological impact. Ketone drinks and BHB supplements, marketed as shortcuts to the benefits of keto, are unlikely to replicate the biology this research actually describes – for better or worse.
The MIT study’s broader message is one of metabolic precision: dietary lipid content, through fatty acid oxidation rather than ketone metabolism, influences intestinal cancer development in ways that differ by tissue type. A diet’s effects on the colon tell you nothing reliable about its effects on the small intestine. Treating any single dietary approach as uniformly safe or uniformly beneficial across all body systems is exactly the interpretive error this research corrects. For anyone following or considering keto, the science now demands a more specific question than “is this diet good or bad?” – it demands asking which tissues, which genes, and which conditions apply to you.
Disclaimer: The author is not a licensed medical professional. The information provided is for general informational and educational purposes only and is based on research from publicly available, reputable sources. It is not intended to constitute, and should not be relied upon as, medical advice, diagnosis, or treatment. Always consult a licensed physician or other qualified healthcare provider regarding any medical condition, symptoms, or medications. Do not disregard, avoid, or delay seeking professional medical advice or treatment because of information contained herein.
AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.