Plant sterols are known to reduce levels of low-density lipoprotein (LDL) cholesterol by stopping absorption in the gut. The soluble fibre glucomannan has been reported to also be cholesterol lowering and could improve glycaemic control.
The new study, published in the April issue of the European Journal of Clinical Nutrition (Vol. 60, pp. 529-537), reports the effects of a granola snack bars formulated with plant sterols and/or glucomannan on cholesterol levels and measures of glycaemic control for 13 diabetic and 16 non-diabetic subjects.
The randomised, double-blind, cross-over study gave subjects with one of four functional bars for 21-day periods, with four week wash-out periods between the supplemented periods.
The granola bars, by Forbes Medi-Tech, were formulated to provide 1.8 grams of plant sterols per day (the reported optimal dose), 10 grams of glucomannan per day, a combination of both, or none (control). An optimal dose for glucomannan is yet to be established. Subjects ate one bar between meals, three times a day.
"Supplementation of glucomannan combined with plant sterols reduced plasma total cholesterol concentrations compared to control," reported corresponding author Peter Jones from McGill University, Canada.
The researchers measured a decrease of almost 12 per cent in the total cholesterol level from the start of the trial for the glucomannan supplement, and a fall of over 17 per cent for the combination supplement. No difference between diabetics and non-diabetics was observed.
LDL-cholesterol levels also decreased after the plant sterol supplementation (3.44 millimoles per litre (mmol/L)), glucomannan (3.16 mmol/L), and the combination supplement (2.95 mmol/L), compared to the control supplements (3.60 mmol/L).
Niether plasma triacylglycerol nor high density lipoprotein (HDL) cholesterol levels were reduced in any study group.
It is clear from the results that the combination treatment was the most effective in reducing both total and LDL cholesterol levels in both diabetic and non-diabetics.
"The cholesterol lowering by the combination of plant sterols and glucomannan may involved a reduction in both cholesterol absorption and synthesis," proposed Jones and colleagues.
Plant sterols are known to suppress intestinal cholesterol absorption. Glucomannan has been proposed inhibit the after-meal peak in insulin which would result in a decrease in cholesterol biosynthesis.
The scientists noted that, contrary to their expectations, there no changes in glycaemic control markers, despite previous reports reporting an association in type-2 diabetics, a disagreement that may be due to the difference in doses.
The subjects were also asked to rate the palatability of the bars and to report any side-effects of the supplementation. Bars containing glucomannan alone or in combination with the plant sterols received the lowest marks in terms of palatability.
"Glucosamine is a soluble fibre that forms a highly viscous gel in aqueous solutions, including saliva," explained Jones and his colleagues.
"This viscous gel plays an important role in its hypoglycaemic and hypocholesterolemic action, but it also creates an undesirable taste and mouth feel," they said.
A majority of subjects also reported an increase in intestinal gas due to glucomannan, as well as other effects such as increased bowel movements and softened stools.
"Given both the possible intestinal side effects and unpalatable texture produced by glucomannan, dosage of glucomannan may play an important role in the acceptance of subjects," concluded the researchers.
According to a recent report from Leatherhead Food International, the heart health market was valued at $3.6 bn (€3.0 bn) market in 2004, and expects that sales will grow by nearly 60 per cent over the period 2004 to 2009, to reach nearly $5.7 bn (€4.7 bn) by 2009.