Phytosterol content of experimental diets differing in fatty acid composition

The goal of this study was to determine the relationship between phytosterol and fatty acid concentrations in experimental diets designed to have particular fatty acid profiles. Diet samples were collected during three National Heart, Lung and Blood Institute sponsored multi-center clinical feeding studies (DELTA and DASH programs). Phytosterols (β-sitosterol, campesterol, stigmasterol, campestanol, sitostanol, avenasterol and brassicasterol) were assayed in the saponified total lipid extracts of diet composites, as trimethylsilyl ether derivatives, by gas chromatography and gas chromatography/mass spectrometry. The predominant phytosterols (>84%) in all diets were β-sitosterol, campesterol and stigmasterol. Regression using a multiple linear model showed an inverse relationship between saturated fat (SFA) and total phytosterols (β1=−2.55; p<0.001), a positive relationship between polyunsaturated fat (PUFA) and total phytosterols (β3=6.53; p<0.03), and no association between total phytosterols and monounsaturated fat (MUFA) (β2=0.55, p<0.40). The results suggest that dietary phytosterol content covaries with changes in PUFA and SFA. Total phytosterol content decreases with increasing SFA and is notably elevated by increasing PUFA. Further studies must elucidate the biological effects of varying phytosterol concentrations as components of different diets. However, clinicians should recognize the likely concurrent variance of phytosterol and fatty acid concentrations in experimental diets, since both have been shown to influence blood cholesterol levels.