Plant Sterols: Evidence to Support a Health Claim

Sylvia Santosa, Suhad AbuMweis and Peter Jones

Introduction

Phytosterols, also termed plant sterols, are natural components of plants that play important roles in cell membrane integrity (1). Structurally, phytosterols are similar to cholesterol, with the only difference being the presence of an extra methyl, ethyl group or double bond (2). Though plant sterols perform similar functions to cholesterol, the slight differences in structure result in intestinal absorption efficiency levels of 2-5% of that consumed, compared to 60% for cholesterol (2). Thus, although average daily dietary intakes phytosterols range from 160-400 mg, only a small fraction of this is absorbed by the human gut (2).

All naturally occurring phytosterols belong to the 4-desmesmethylsterol family and include beta-sitosterol, campesterol and stigmasterol (1, 2). Sitostanol is a hydrogenated phytosterol usually found in the extract of pine wood pulp (1). Esterifying phytosterols and phytostanols to fatty acids results in increased lipid solubility (3). As a result of increased lipid solubity, esterified plant sterols are thought to enhance effectiveness of lipid lowering, though this has recently shown to be untrue (2, 3).

In September 2000, the Center for Food Safety and Applied Nutrition Branch of the FDA passed a 12th health claim for foods containing plant sterol and stanyl esters and coronary heart disease (CHD) risk reduction (4). Foods carrying the claim were required to contain 0.65 g of phytosterol ester of 1.7 g or phytostanol ester per serving with at least two servings eaten at different times of the day, resulting in total consumption of 1.3 g/d and 3.4 g/d, respectively (4). Even more recently, the National Cholesterol Education Program (NCEP) has recommended consumption of plant sterols at 2 g/d in addition to the Therapeutic Lifestyle Change Diet to lower elevated low density lipoprotein cholesterol (LDL-C) levels. Products, such as margarine, that contain free and esterified plant sterols are currently being sold in many countries (4). This paper will explore the validity of health claims currently surrounding these products. In doing so, the usefulness of phytosterols and phytostanols in cholesterol lowering and CHD risk reduction to clinical practice will be explored.

Phytosterols May Reduce the Risk of Heart Disease

Consumption of 2 g/d of sterols or stanols has been suggested to decrease risk reduction of CHD by 25% (5). This reduction in risk is more significant than that which would be achieved through reducing intake in saturated fats. More recently, Moreau, Whitaker & Hicks (4) cite a paper implicating the supplementation of 3 g/d of esterified stanols or sterols in decreasing CHD risk by 15-40%.

However, no supplementation trials exist that use CHD associated event or death endpoint. Thus, the protective effect of plant sterols on CHD event or death cannot be established with certainty. In order to conduct a clinical trial that would detect a 12