The first clinical study to demonstrate oats exerting a hypolipidaemic effect was published in The Lancet in August 1963. The Dutch research team replaced 300g/day of conventional bread with an equal portion of bread containing 140g of rolled oats, consumed over three weeks among a cohort of 21 healthy hyperlipidemic males.1 This produced an average drop of 8.9 per cent in serum total cholesterol by the third week.

A multitude of subsequent clinical trials has illustrated the modest lipid-lowering efficacy of the oat archetype, oatmeal, and its offspring, oat bran. More investigations into the cereal chemistry of oats and other grains (eg, barley) ascribed the lipid-modifying effects to that of the beta-glucans (BGs) present. Oat-derived BGs have created a renaissance in fibre ingredients and functional foods production, buoyed by the approval of a blood lipids/cardiovascular health claim in the US in 1997. The consensus that BGs comprise the primary (if not sole) hypolipidaemic fraction in oats has fostered the vigorous pursuit of cultivars, processing and characterization strategies centering upon the concentration of BGs in speciality oat-derived bioactives. Indeed, the concentration and molecular weight of BGs varies on a regiospecific, cultivar, growing conditions, processing and harvest year basis.2^,3

Daily consumption of 3g of BGs (from 20g oat bran concentrate; Nestlé, Switzerland; mixed into low-fat yoghurt or milk) by 31 hyperlipidaemic men and women failed to elicit a greater change in plasma lipids after 12 weeks, compared to a wheat-bran placebo.4 Additionally, HDL cholesterol dropped significantly in the BGs group at week eight. It is germane to note that this 3g BGs dose is the minimum threshold dose associated with the aforementioned health claim issued by the Food and Drug Administration.

It appears commonplace for marketers of oat-derivatives with high BGs to describe the clinical research literature as a body of evidence supporting 'oat BGs,' where in fact the vast majority of the literature resides with oatmeal and oat bran concentrate. In one of the few controlled clinical trials conducted with a high concentration oat BGs supplement, 20 hyperlipidaemic men and women were asked to consume a beverage (twice daily) to which they added 2.9g of BGs (from oat gum; 80 per cent BGs; total of 5.8g BGs/day) or a maltodextrin placebo beverage, for four weeks.5 Total and LDL cholesterol dropped significantly in the oat gum group by week four, by nine and 10 per cent. A more recent study used an oat derivative with 54 per cent BGs (OatVantage, Nurture, USA), among a sample of 90 modestly hyperlipidaemic men and women.⁶ Subjects were asked to consume either 3g of dextrose placebo or 3g of this oat derivative blended into a beverage, at morning and night (total daily dose of 3.2g of BGs). After six weeks, LDL cholesterol exhibited a significantly greater decline (nine per cent) in the oat group compared to placebo, while total cholesterol changes were not significantly different between groups. Additionally, no difference was seen between groups in HDL cholesterol, fasting glucose or insulin, homocysteine, or C-reactive protein. What remains to be unequivocally demonstrated is whether a 'practical' or tolerable dose of oat-derived BGs indeed can exert a persistent hypolipidaemic effect.

One additional biological activity often ascribed to oat BGs is immune-response modification. However, there appear to be no randomised controlled trials validating this assertion. In a recent study, pooled ileostomy effluent from six subjects after random consumption of a diet with or without a daily intake of 6g of BGs from oats (source not defined) was exposed to several different intestinal cell lines.⁷ The diet with BGs produced a marked pro-inflammatory response, which reinforces the need to explore the immunoaugmentative impact of oat-derived BGs.

References
1. De Groot AP, et al. Cholesterol-lowering effect of rolled oats. Lancet 1963; 282:303-4.
2. Ajithkumar A, et al. Content and molecular weight of extractable 3/4-glucan in American and Swedish oat samples. J Agric Food Chem 2005; 53:1205-9.
3. Bennett CS and Cleary LJ. The potential use of cereal (1-3,1-4)-3/4-D-glucans as functional food ingredients. J Cereal Sci 2005; 42: 1-13.
4. Lovegrove JA, et al. Modest doses of 3/4-glucan do not reduce concentrations of potentially atherogenic lipoproteins. Am J Clin Nutr 2000 ; 72:49-55.
5. Braaten JT, et al. Oat beta-glucan reduces blood cholesterol concentrations in hypercholesterolemic subjects. Eur J Clin Nutr 1994; 48:465-74.
6. Queenan K, et al. Practical dose of concentrated beta-glucan from oats improves blood lipid profile. FASEB J 2005; 19:A89.
7. Smith KN, et al. Comparison of barley beta-glucan vs placebo in hypercholesterolemic subjects. FASEB J 2005; 19:A89.

Anthony Almada, MSc, is president and chief scientific officer of IMAGINutrition. Respond: [email protected]