We examined the role of common genetic variation in determining the consistency and magnitude of change in plasma total cholesterol (TC) levels in response to two separate changes from a high-saturated (SFA) to a low-saturated/high-polyunsaturated-fat (PUFA) diet, in a group of free-living healthy men and women. Consistent responders were defined as those whose mean difference in the change in TC was within one SD of the mean for all participants, and the remainder were defined as variable responders. DNA was obtained from 55 individuals and genotype determined at the apolipoprotein (apo) B locus (signal peptide, SP), apoCIII (C1100-T) and lipoprotein lipase (LPL) gene loci (HindiIII). In the 38 consistent responders, the apoBSP24 allele was significantly more common than in the 17 individuals with a variable response (0.29 vs. 0.12; p < 0.05). No other polymorphism showed a significant frequency difference between groups. In the group as a whole, the correlation between the change in TC level in response to the first and second dietary change was 0.28 (p = 0.05), but those with one or more apoB SP24 alleles and those with the apoCIII genotype CC had a significantly higher correlation than those with other genotypes (0.46 (p = 0.05) vs. 0.12 (NS) and 0.31 (p= 0.05) vs. 0.02 (NS), respectively). In the group as a whole, mean response left TC 10 higher on the SFA than on the PUFA diet, and neither apoB nor apoCIII genotypes affected the magnitude of this response. However, individuals with the LPL HindIII genotype H~+ H~+ had a significantly smaller change in mean TC in response to diet than those with one or more H~- allele (9.3 vs. 14.4; p = 0.03). Thus variation at the apoB and apoCIII loci affects the consistency of response to change in dietary fat content, while variation at the LPL gene locus affects magnitude of response.
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