UCSF

Background

A carbohydrate-restricted (CR) diet can improve glycemic control in people with type 2 diabetes mellitus (T2DM). There are concerns, however, that the high dietary fat content of CR diets can increase low-density lipoprotein cholesterol (LDL-C), thus increasing cardiovascular disease (CVD) risk. Quantifying CVD risk associated with changes in LDL-C in the context of CR diets is complicated by the fact that LDL-C reflects heterogeneous lipids. For example, small LDL particle number (sLDL-P) is more closely associated with CVD risk than is total LDL-C, and CR diets tend to decrease the proportion of sLDL-C in LDL-C, which standard lipid measures do not indicate. Advanced lipoprotein assays, such as nuclear magnetic resonance (NMR) testing, can subfractionate lipoproteins by size and density and may better depict the effects of CR diets on CVD risk.

Methods

Adults (N = 58) with T2DM (n = 37 women; baseline HbA1c ≥ 6.5%) completed a 6-month group-based CR diet intervention. We obtained a standard lipid panel, advanced lipoprotein assays (NMR testing), and two 24-h diet recalls at baseline and post-intervention (6 months). Participants also completed home-based blood ketone testing (a biological index of dietary adherence) during the final five weeks of the intervention.

Results

From baseline to post-intervention, participants had increased mean HDL-C, decreased triglycerides and triglyceride/HDL ratio, decreased mean sLDL-P, and increased LDL size, which reflect reductions in CVD risk (ps < 0.05). Participants did not have statistically significant changes in total cholesterol, non-HDL-C cholesterol, LDL-P, or HDL-P. Twelve participants (23.1%) had a ≥ 5% increase in sLDL-P. Exploratory analyses revealed that participants with sLDL-P increases of ≥ 5% reported larger increases in servings of red meat than participants without sLDL-P increases of ≥ 5% (+ 0.69 vs - 0.29 servings; p = 0.033). Changes in saturated fat intake were not associated with changes in sLDL-P.

Conclusions

Among most participants, we observed changes in several lipid measures consistent with decreased CVD risk. Approximately one in four participants evidenced increases in sLDL-P. Further research should clarify whether individuals with increased sLDL-P after implementing a CR diet can reverse observed increases by limiting red meat consumption.

Trial registration

ClinicalTrials.gov, NCT03207711, Registered 6/11/2017. Retrospectively registered.