Why Does LDL Cholesterol Rise on Keto? The Lean Mass Hyper-Responder Phenomenon

Some people start keto and, a few months in, see their LDL cholesterol spike to 250-300 mg/dL. Often these are lean, active individuals with normal blood sugar and blood pressure — they don't fit the usual "high-risk" picture at all. Many doctors, seeing this, say "stop keto immediately." But research on this specific phenotype over the past few years shows the picture is more nuanced than that — and goes beyond the "large LDL particles are harmless" simplification you'll see in our own blood test effects article.

What Is a Lean Mass Hyper-Responder (LMHR)?

The term was coined by researcher Dave Feldman and the Citizen Science Foundation. The definition rests on three thresholds on a keto/low-carb diet: LDL cholesterol ≥200 mg/dL, HDL cholesterol ≥80 mg/dL, and triglycerides ≤70 mg/dL. This profile shows up especially in lean, metabolically healthy people with a low triglyceride-to-HDL ratio. The proposed mechanism, the "Lipid Energy Model," suggests that on a low-carb diet the liver transports fat to tissues via VLDL/LDL particles for energy, and that this transport is more pronounced in lean people with high fat oxidation. The model is debated and isn't proof on its own.

2024: What Did the KETO Study Find?

The 2024 KETO study published in JACC: Advances (Budoff et al.) compared 80 LMHR/near-LMHR individuals with LDL ≥190 mg/dL to a control group from the Miami Heart cohort, matched for age, sex, race, blood pressure and smoking status but with much lower LDL. Participants had been on keto for an average of 4.7 years. The finding was notable: on CT coronary angiography, the LMHR group did not show more coronary plaque than the much-lower-LDL control group. This was read as partial support for the idea that "not all high LDL carries the same risk."

2025-2026: The Follow-Up and Its Retraction

The same team then ran a one-year follow-up (KETO-CTA), tracking LMHR/near-LMHR individuals with repeat CT angiography. The results, published in 2025, reported a roughly 50% relative annual increase in soft (non-calcified) plaque volume — about 2.5 times higher than the researchers had pre-specified as their expectation, and by some readings faster than progression rates seen in people with metabolic syndrome. However, the paper was published under a headline emphasizing that "past plaque predicts future plaque, ApoB does not," without adequately addressing this pre-registered primary outcome — a framing that drew criticism.

In 2026, a problem surfaced in how the imaging had been analyzed. Both the authors and the journal's editors agreed the error was too significant to fix with a correction, and the paper was retracted. So what we're left with is a study that reported plaque growth but is now flagged by the journal as unreliable — even though it's still being shared online in its original form.

So What's the Real Picture?

The honest answer: it isn't settled yet. The 2024 study found no excess plaque in LMHR individuals after an average of ~5 years on keto — a reassuring signal. But that doesn't mean "LDL is harmless no matter how high it goes" — the sample was small (80 people) and the follow-up period is limited for judging lifetime risk. The 2025 follow-up pointed the other way, but it was retracted for a methodological problem — meaning that data is no longer considered reliable, though it doesn't mean the underlying question was never raised. Researchers in the field remain divided.

Who Should Be More Cautious?

• Anyone with a family history of early heart attack or stroke — the LMHR phenotype doesn't rule out familial hypercholesterolemia; that requires genetic testing or specialist evaluation
• Anyone who already has calcified plaque (a high CAC score) — even in the retracted version of KETO-CTA, the subgroup with baseline CAC>100 showed faster progression; this specific subgroup finding warrants extra caution on its own
• Anyone with LDL above 300 mg/dL — the LMHR definition has no upper bound, and a more cautious approach is recommended at extreme levels
• Anyone with additional risk factors like diabetes, smoking, or uncontrolled blood pressure — the LMHR data doesn't cover these groups, so results can't be generalized to them

What Should You Do?

If your LDL has risen noticeably on keto, the first move isn't to panic and quit the diet — but it also isn't to tell yourself "I'm an LMHR, so it's fine." Work with your doctor: review your family history, consider checking ApoB or lipoprotein(a), and discuss imaging options like a coronary calcium (CAC) score or CT angiography. Some doctors let patients who fit the LMHR profile continue the diet with regular imaging follow-up; others recommend a more cautious dietary adjustment. Both approaches have advocates in the literature — the decision should be made with your doctor, based on data and your own risk profile.