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Phytosterols that are naturally present in commercial corn oil significantly reduce cholesterol absorption in humans^1,2,3

¹ From the Division of Endocrinology, Diabetes and Metabolism (REO Jr and AO), the Division of Geriatrics and Gerontology (SBR), and the Division of Gastroenterology, Department of Internal Medicine (WFS), Washington University, St Louis.

Background: Although supplementing the diet with large quantities of phytosterols reduces cholesterol absorption and LDL-cholesterol concentrations, very little is known about the smaller amounts of phytosterols present naturally in food. Vegetable oils are the richest dietary source of phytosterols; corn oil contains 0.77% phytosterols by weight.

Objective: We tested the hypothesis that removing phytosterols from corn oil would increase cholesterol absorption when measured in single-meal tests containing corn oil as a source of fat.

Design: Free and esterified phytosterols were removed from corn oil on a kilogram scale by a new technique of competitive saturation adsorption to silica. Healthy subjects with a mean (±SEM) serum cholesterol concentration of 5.10 ± 0.18 mmol/L received an otherwise sterol-free test breakfast on 2 occasions 2 wk apart that contained 35 mg hexadeuterated cholesterol and 30–35 g of a corn oil preparation. The plasma enrichment of tracer was measured by negative ion mass spectrometry.

Results: Cholesterol absorption was 38.0 ± 10.2% higher after consumption of the sterol-free corn oil than after consumption of commercial corn oil with an identical fatty acid content (P = 0.005; n = 10). When corn oil phytosterols were added back to sterol-free corn oil at a concentration of 150 mg/test meal, cholesterol absorption was reduced by 12.1 ± 3.7% (P = 0.03; n = 5) and by 27.9 ± 9.1% (P = 0.01; n = 10) after inclusion of 300 mg phytosterols.

Conclusions: Phytosterols comprising < 1% of commercial corn oil substantially reduced cholesterol absorption and may account for part of the cholesterol-lowering activity of corn oil previously attributed solely to unsaturated fatty acids.

Key Words: Phytosterols • oils • diet • cholesterol • mass spectrometry • deuterium

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