Understanding the LMHR phenotype and Implications for Risk Stratification
Identifying Patients Who May Not Fit Standard Profiles
A growing subset of patients — often lean individuals adopting ketogenic or carbohydrate-restricted diets — present with markedly elevated LDL-C or ApoB yet maintain otherwise pristine metabolic health.
Patients with:
- Triglycerides <70 mg/dL
- HDL-C >80 mg/dL
- LDL-C >200 mg/dL
…are often referred to as Lean Mass Hyperresponders (LMHR).
Emerging data suggest that in these individuals, current plaque burden — not isolated LDL-C or ApoB — may be the strongest predictor of short-term risk. Coronary Artery Calcium (CAC) scoring offers particular utility in this context to guide management decisions and discussions around whether or not medications may be helpful.
In LMHR patients, elevated LDL-C or ApoB could reflect increased fat-based energy trafficking rather than a maladaptive response driven by insulin resistance, inflammation, metabolic syndrome, or broken genes.
This phenotype appears metabolically distinct from typical hyperlipidemia, and risk assessment strategies should reflect that nuance.
Metrics & Tests That Matter
Key markers to consider when evaluating patients with isolated high LDL-C include:
- Fasting Insulin: Often low in Lean Mass Hyperresponders (LMHR), reflecting high insulin sensitivity and efficient energy use. Elevations may signal early metabolic dysfunction before changes in glucose or lipids.
- Triglyceride to HDL-C Ratio: A practical and inexpensive marker of insulin resistance. A ratio close to 1 (or lower) is strongly associated with favorable metabolic health. LMHR individuals frequently have ratios well below 1.
- Coronary Artery Calcium (CAC) Score: The most powerful tool for 5-year time frame ASCVD risk stratification in this population. A CAC score of 0 is highly reassuring, even with markedly elevated LDL-C or ApoB. Presence of plaque (CAC >0) may shift management toward risk reduction strategies.
Importantly, data from the Western Denmark Registry (n >11,000; ~4-year follow-up) showed no association between LDL-C levels and ASCVD events — even comparing LDL-C <116 mg/dL to LDL-C >193 mg/dL — when baseline plaque burden was absent ie CAC = 0. However, once CAC >0 was present, LDL-C became strongly associated with future events — with those individuals with higher LDL-C experiencing a 2.42x higher risk of ASCVD events.
Clinical Vignette: Contextualizing Elevated LDL-C in a Lean, Metabolically Healthy Adult
A 40-year-old male presents for evaluation after recent laboratory testing revealed an LDL-C of 192 mg/dL and ApoB of 122 mg/dL. He has been following a ketogenic diet for the past 2 years with profound improvement in debilitating depression. He reports no family history of premature atherosclerotic cardiovascular disease (ASCVD), is a non-smoker, and exercises regularly.
His BMI is 22 kg/m². He feels well with excellent functional capacity. He expresses a preference to avoid medications unless there is clear evidence of benefit.
Additional labs reveal:
- Triglycerides: 52 mg/dL
- HDL-C: 80 mg/dL
- TG/HDL-C ratio: 0.65
- Fasting insulin: 2.5 µIU/mL
- HbA1c: 5.0%
- hsCRP: <0.1mg/dl
These findings suggest a metabolic environment characterized by high insulin sensitivity, low visceral adiposity, and a favorable lipid partitioning profile — a context in which elevated LDL-C may reflect increased reliance on fat-based energy trafficking rather than metabolic dysfunction or insulin resistance.
Given his preference to avoid pharmacotherapy and the known limitations of using LDL-C alone to stratify risk in this unique phenotype, coronary artery calcium (CAC) scoring was recommended for further risk assessment.
His CAC score returned 0 and after discussing the risks/benefits with his provider, he has elected to defer medications and recheck his calcium score in 3 years.
Addressing Patient Questions & Misconceptions
Some patients may contend that LDL-C or ApoB “don’t matter” for heart disease risk — particularly within low-carb or ketogenic communities.
It’s important to clarify that the risk conferred by LDL-C or ApoB is not binary — rather, it’s likely a function of current disease burden (See Western Denmark Registry above).
Clinical Message
Patients with no detectable plaque (CAC = 0) may reasonably consider lifestyle-first strategies and close monitoring.
Patients with any measurable plaque (CAC >0) should have a shared decision-making discussion about risk-reducing medications — especially therapies with proven event reduction (e.g., statins, ezetimibe, PCSK9 inhibitors).
Encourage patients to work closely with their healthcare providers to tailor a plan that aligns with their values and risk profile.