Triglyceride content increases while cholesterol content decreases in HDL and LDL+IDL fractions following normal meals: The Copenhagen General Population Study of 25,656 individuals

Abstract

Background and aims: During fat tolerance tests, plasma triglycerides increase while high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, and intermediate-density lipoprotein (IDL) cholesterol decrease. However, it is unknown whether triglyceride content increases and cholesterol content decreases in HDL and LDL + IDL fractions following normal meals in the general population. Therefore, we tested the hypothesis that triglyceride content increases while cholesterol content decreases in HDL and LDL + IDL fractions following normal meals.

Methods: In this cross-sectional study, we included 25,656 individuals aged 20-100 years, all without lipid-lowering therapy at examination and selected for metabolomic profiling from the Copenhagen General Population Study. Triglyceride and cholesterol content of 14 lipoprotein fractions weas measured using nuclear magnetic resonance (NMR) spectroscopy. Time since last meal was recorded by the examiner immediately before blood sampling.

Results: Following normal meals in age and sex-adjusted analyses and when compared with fasting levels, plasma triglycerides were higher for up to 5-6 h, and triglyceride content was higher for up to 6-7 h in HDL fractions, for up to 6-7 h in LDL + IDL fractions, and for up to 5-6 h in very-low-density lipoprotein (VLDL) fractions. Further, plasma cholesterol was lower for up to 2-3 h, and cholesterol content was lower for up to 0-1 h in HDL fractions and for up to 4-5 h in LDL + IDL fractions, while cholesterol content was higher for up to 4-5 h in VLDL fractions.

Conclusions: Following normal meals, triglyceride content increases while cholesterol content decreases in HDL and LDL + IDL fractions.

Keywords: Apolipoproteins; Cardiovascular disease; General population; Lipids; Lipoprotein subfractions; Postprandial.

Figure 1. Triglycerides, cholesterol, and lipoprotein particle number in plasma and in main lipoproteins fractions according to time since the last meal.

Dots represent quadratic means adjusted for age and sex and error bars represent 95% confidence intervals. Plasma triglycerides and plasma cholesterol were measured on fresh blood samples using routine hospital assays. Triglyceride and cholesterol content in lipoprotein fractions were measured using nuclear magnetic resonance spectroscopy and corrected for recovery. The y-axes are on a logarithmic scale. Bonferroni corrected p-values based on 8 parallel tests using unpaired Student t-test versus fasting levels (≥8 hours) are as follows: *p<0.05; **p<0.01; ***p<0.001. Abbreviations: HDL: high-density lipoproteins. IDL: intermediate-density lipoproteins. LDL: low-density lipoproteins. VLDL: very low-density lipoproteins.

Figure 2. Concentrations of triglycerides in lipoproteins fractions according to time since last meal.

Dots represent quadratic means adjusted for age and sex and error bars represent 95% confidence intervals. Triglyceride content in lipoprotein fractions were measured using nuclear magnetic resonance spectroscopy and were corrected for recovery. Bonferroni corrected p-values based on 8 parallel tests using unpaired Student t-test versus fasting levels (≥8 hours) are as follows: *p<0.05; **p<0.01; ***p<0.001. Smallest HDL include S+M HDL. Largest HDL include L+XL HDL. Abbreviations: HDL: high-density lipoproteins. IDL: intermediate-density lipoproteins. L: large. LDL: low-density lipoproteins. M: medium. S: small. VLDL: very low-density lipoproteins. XL: extra large. XS: extra small. XXL: extra extra large.

Figure 3. Cholesterol in main lipoprotein fractions along with plasma triglycerides according to time since last meal.

Dots represent quadratic means adjusted for age and sex and error bars represent 95% confidence intervals. Plasma triglycerides were measured on fresh blood samples using routine hospital assays. Cholesterol content in lipoprotein fractions was measured using nuclear magnetic resonance spectroscopy and was corrected for recovery. Left y-axis shows lipoprotein cholesterol concentration; right y-axis shows plasma triglyceride concentration. Bonferroni corrected p-values based on 8 parallel tests using unpaired Student t-test versus fasting levels (≥8 hours) are as follows: *p<0.05; **p<0.01; ***p<0.001. Smallest HDL include S+M HDL. Largest HDL include L+XL HDL. Smallest LDL include S+ M LDL. Smallest VLDL include XS+ S VLDL. Largest VLDL include M+ L+XL+ XXL VLDL. Abbreviations: HDL: high-density lipoproteins. IDL: intermediate-density lipoproteins. L: large. LDL: low-density lipoproteins. M: medium. S: small. VLDL: very low-density lipoproteins. XL: extra large. XS: extra small. XXL: extra extra large.

Figure 4. Triglycerides, cholesterol, and lipoprotein particle number in plasma and in main lipoproteins fractions according to time since the last meal in individuals with normal weight and overweight/obesity separately.

Dots represent quadratic means adjusted for age and sex and error bars represent 95% confidence intervals. Plasma triglycerides and plasma cholesterol were measured on fresh blood samples using routine hospital assays. Triglyceride and cholesterol content in lipoprotein fractions were measured using nuclear magnetic resonance spectroscopy and corrected for recovery. The y-axes are on a logarithmic scale. Bonferroni corrected p-values based on 8 parallel tests using unpaired Student t-test versus fasting levels (≥8 hours) are as follows: *p<0.05; **p<0.01; ***p<0.001. Abbreviations:HDL: high-density lipoproteins. IDL: intermediate-density lipoproteins. LDL: low-density lipoproteins. VLDL: very low-density lipoproteins.