It’s a question that comes up again and again: Could Lean Mass Hyper-Responders (LMHRs) just be eating more saturated fat?
Rather than repeatedly answering this question in cumbersome Twitter threads, I thought I’d save both Dave and myself some time by consolidating 5 points that challenge the saturated fat hypothesis of LMHR:
1. Magnitude of effect. Many LMHRs exhibit LDL-C levels of well over 300 mg/dl. Mean levels from the LMHR participants in our cohort study were 320 mg/dl (Table 3), and we certainly have a handful with LDL-C above 500 mg/dl. I’m not aware of any data suggesting saturated fat intake, even at extreme levels, can cause increases in LDL-C to such an extent. If you – the reader – are aware of such data, please do share.
2. LDL-C change has an inverse relationship to BMI. In the same study, we observed that LDL-C change has an inverse relationship to BMI on a carbohydrate restricted diet. If this is the case and saturated fat was the primary driver of the increase in LDL-C observed, then the logical implications are either that there is a dose-response effect of saturated fat on body weight loss (i.e. saturated fat makes subjects leaner) OR that persons who are lean and adopt low-carb diets preferentially eat higher proportion saturated fat diets. For example, if we had three subjects, Jamie, Nicky, Leslie, and Amir with BMIs of 24, 26, 21, and 30, respectively, and they were all to adopt low-carb diets, Leslie would eat more saturated fat than Jamie who would eat more saturated fat than Nicky who would eat more saturated fat than Amir.
3. The triad. A critical point is that LMHR are defined, not by LDL-C alone, but the triad of high LDL-C, high HDL-C and low triglycerides. Therefore, any complete model explaining the LMHR phenomenon must account for this triad. Thus, we must ask, could eating more saturated fat cause to the triad of markers seen in LMHR? (And that’s assuming LMHR eat primarily high-saturated fat low-carbohydrate diets.) In our study, mean levels were 320 mg/dl LDL-C, 99 mg/dl HDL-C, and 47 mg/dl triglycerides.
4. Adding back moderate carbs attenuates the phenotype. In the case series associated with the aforementioned study, six LMHR or near-LMHR subjects were instructed to introduce 50-100g/d carbs to help replenish hepatic glycogen and, via the postulates of the Lipid Energy Model, lower their LDL-C. No further instructions were given, i.e. subjects were not told to lower saturated fat intake. Nevertheless, all subjects exhibited substantial reductions in LDL-C, including one who exhibited a drop from 665 mg/dl to 185 mg/dl. Even if saturated fat intake occurred spontaneously (without instruction), it seems unlikely it could explain the magnitude of the effect.
5. Case series. Although it is an n = 1, we published a case series of an individual consuming a ketogenic diet relatively low in saturated fat (~82% unsaturated, ~18% saturated). His pre-low carb LDL-C was 95 mg/dl. But following carb reduction, LDL-C rose to a peak of 545 mg/dl, despite relatively low saturated fat intake. Furthermore, LDL-C trended inversely with BMI and, when saturated fat intake was altered for experimental purposes, LDL-C remained concordant with the BMI trend and, thus, inconsistent with the prediction that saturated fat drives LDL-C change in this subject. Even if this is only a case report, recall that these data represent a real LMHR patient and are consistent with both the LMHR cohort study and the Lipid Energy Model.
Certainly, none of these 5 points dispute that saturated fat could contribute to the increase in LDL-C seen in LMHR; however, they do suggest that saturated fat is not the primary driver of change. Disregarding point 5, could high saturated fat intake be permissive or even required for the LMHR phenotype? Possibly. However, unless one can explain how saturated fat intake could account for these data, we should assume there is more at play worth investigating.
For more reading and viewing:
Lipid Energy Model: https://www.mdpi.com/2218-1989/12/5/460
Lipid Energy Model video abstract: https://youtu.be/AkzxESsTJyM
Lean Mass Hyper Responder study: https://academic.oup.com/cdn/article/6/1/nzab144/6446805
Lean Mass Hyper Responder video abstract: https://youtu.be/v4FXBtVXPhA
Lean Mass Hyper Responder Case report: https://www.frontiersin.org/articles/10.3389/fendo.2022.830325/full
Lean Mass Hyper Responder Case report video abstract: https://youtu.be/JSEqIsYBZxU