Scientific Opinion on the substantiation of health claims related to
glucomannan and maintenance of normal blood cholesterol concentrations
(ID 836, 1560) pursuant to Article 13(1) of Regulation (EC) No 1924/2006[sup]1[/sup]
EFSA Panel on Dietetic Products, Nutrition and Allergies2,
European Food Safety Authority (EFSA), Parma, Italy
Słowa kluczowe:
Glucomannan
Konjac mannan
blood cholesterol
health claims
3. Naukowe uzasadnienia wpływu na zdrowie człowieka - Zmniejszenie stężenia cholesterolu we krwi
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Regularne spożywanie glukomannanu pomaga utrzymać prawidłowe stężenie cholesterolu we krwi
Eight randomised controlled trials, which investigated the effects of glucomannan on LDL and/or total cholesterol at daily doses of 3-15 g/d in either healthy, hypercholesterolaemic or diabetic adult human subjects, were provided.
Zhang et al. (1990) randomised 110 elderly subjects with hyperlipidaemia to consume glucomannan- rich foods at doses 5-10 g/d glucomannan in addition to their usual diet (n=66) or their usual diet only (n= 44, controls) for 45 days. Serum total and LDL-cholesterol concentrations significantly decreased (by about 7%) in the glucomannan group as compared to controls at the end of the study.
Arvill and Bodin (1995) found a 10 % reduction in serum total cholesterol concentrations and a 7% reduction in LDL-cholesterol concentrations with 3.9 g/d glucomannan (n= 32) as compared to placebo (n = 31) in healthy men (parallel comparison). The study was planned to be a crossover trial with two 4-week intervention periods and a 2-week washout period. However, the results of the second intervention period (after cross-over) were not reported in the publication. The reason given was a carryover effect in the glucomannan group.
In the study by Vuksan et al. (1999), 11 diabetic subjects were given 0.7 g/100 kcal (on average 15 g/d) glucomannan and wheat bran (control) in a crossover comparison over periods of 3 weeks with a one-week washout period in between. During the glucomannan period, the total/HDL cholesterol ratio was significantly reduced as compared to the wheat bran control period. Serum total cholesterol and LDL-cholesterol concentrations appeared to be reduced during the glucomannan period by 11 % and 7 %, respectively, but the changes were not statistically significant as compared to the wheat bran control after Bonferroni adjustment for multiple comparisons.
In a second controlled crossover study by the same group of investigators with similar design, 11 subjects with the metabolic syndrome were randomly assigned to consume either glucomannan fibre– enriched test biscuits (0.5 g of glucomannan per 100 kcal of dietary intake or 8–13 g/day) or wheat bran fibre (control) for 3 weeks, each separated by a 2-week washout. Serum total cholesterol was significantly reduced by 12.4 % and LDL-cholesterol by 22 % during the glucomannan intervention as compared to the wheat bran (control) intervention (Vuksan et al., 2000).
In another study, 22 type 2 diabetic subjects with elevated blood cholesterol concentrations but not on lipid-lowering medication were recruited to participate in a two 28-day period, randomized, double- blind, crossover clinical trial. Glucomannan at doses 3.6 g/d significantly reduced serum cholesterol
concentrations by 11 % and LDL-cholesterol concentrations by 20 % as compared to placebo (Chen et al., 2003).
In a placebo-controlled crossover study consisting of four phases of 21 days, each phase separated by a 28-day washout, Yoshida et al. (2006) investigated the effects of glucomannan, both alone and in combination with plant sterols, in mildly hypercholesterolaemic non-diabetic (n=18) and type II diabetic (n=16) individuals aged 38-74 years. Results showed a significant 9.5% reduction in serum total cholesterol and a significant 11% reduction in serum LDL-cholesterol with 10 g/d glucomannan (alone) as compared to placebo.
Using a parallel-arm, double-blind, placebo-controlled design, 30 overweight and obese men were randomly assigned to consume either glucomannan (3g/d, n = 15) or placebo (n = 15) for 12 weeks in the context of a low-carbohydrate diet for weight loss (Wood et al., 2007). Results showed a small significant 4% reduction in serum total cholesterol and a significant 8% reduction in serum LDL- cholesterol in the glucomannan group as compared to placebo, with no significant effect on the total/HDL-cholesterol ratio.
In a randomized, placebo-controlled trial (Martino et al., 2005), 40 hypercholesterolaemic children
below 14 years of age were randomly allocated to consume glucomannan (2 g/d to children 6y of age, 3 g/d to children > 6y of age) in gelatine capsules or no capsules (control) in the context of a Step-One-Diet for 8 weeks. Serum total cholesterol and LDL-cholesterol significantly decreased in the glucomannan group as compared to controls after 8 weeks of intervention. The percentage decrease showed a statistically significant difference between sexes. Decreases were observed in female and male children respectively in total (24% vs. 9%) and LDL-cholesterol (30% vs.9%).
An additional study, designed to test the effects of glucomannan consumption on blood lipids with or without physical exercise, was presented (Kraemer et al., 2007). However, the Panel notes that there was no control group, and therefore no conclusions can be drawn form this study in relation to the claimed effect.
The effect of water-soluble fibre types, such us glucomannan, on blood cholesterol probably depends on viscosity, which reduces the re-absorption of bile acids, increases the synthesis of bile acids from cholesterol, and reduces circulating (LDL) cholesterol concentrations. Glucomannan has a high viscosity and high molecular weight and physiological effects seem to be similar to other types of high-viscosity water-soluble fibres (Jenkins et al., 2000).
In weighing the evidence, the Panel took into account that a statistically significant effect on either total or LDL-cholesterol was not observed following the consumption of glucomannan in all of these studies, that reduction in total and/or LDL-cholesterol concentrations did not always lead to significant reductions in the total/HDL cholesterol ratio, that the vast majority of these studies had small samples sizes, and that no clear dose-response relationship was established between the consumption of glucomannan and the claimed effect. However, the Panel considers that most studies showed a consistent effect in the reduction of serum total and LDL-cholesterol concentrations at doses of about 4g/d of glucomannan, that the effect has been observed not only in hypercholesterolaemic subjects but also in normocholesterolemic individuals, and that the mechanisms by which the consumption of the food may exert the claimed effect (biological plausibility) are established.
The Panel concludes that a cause and effect relationship has been established between the consumption of glucomannan and the reduction of blood cholesterol concentrations.
