Evidence suggests that fibre is beneficial to the health because it reduces the risk of cardiovascular disease. This effect may be due to the blood sugar stabilising effects of the fibre which reduce the risk of metabolic syndrome, a known risk factor for developing vascular disease. Some viscous soluble cereal fibres might be particularly beneficial because they decrease glucose absorption rates by creating a physical barrier in the unstirred layer adjacent to the enterocytes. The β-glucan fibre in oats and barley is one such soluble fibre that has been researched for its effects on cardiovascular disease risk factors. In particular, β-glucan fibre may lower plasma lipid levels as a result of the beneficial glycaemic effects of the fibre. Because higher molecular weight fibres are more viscous, researchers have tested β-glucan fibre of differing molecular weights to assess their effects on blood lipid profiles.
For example, researchers1 have administered either low molecular weight (~62,000 Da) or high molecular weight (~139,000 Da) barley β-glucan fibre to 90 hypercholesterolaemic men and women as a daily supplement of 6g/d for 6 weeks. There was no significant change from baseline in any of the parameters measured in the high molecular weight group. However, in the low molecular weight group significant reductions in low density lipoprotein cholesterol (LDL), C-reactive protein and calorie intake, and significant increases in body weight, were reported. The high molecular weight group also had a significant decrease in bodyweight (0.41kg), despite no change to energy intake. Theses changes in body weight were accompanied by significant decreases in lunchtime hunger from baseline, whereas the low molecular weight group had no significant changes in hunger rating. Very minimal changes to blood lipids may suggest the fibre intake in this study was too low.
These results suggests that different molecular weight β-glucan fibres may have different physiological effects, but that these effects are subtle and not fully understood. The molecular weight of the β-glucan fibre naturally found in barley is around 150,000 to 300,000 Da, but manufacturers can alter the molecular weight of β-glucan fibre by using β-glucanase enzymes. This is increasingly being done when β-glucan fibre is used in food manufacturing due to undesirable sensory traits in the higher molecular weight fibres. This study was inconclusive, but shows generally that the molecular weight of fibres may have different physiological effects. Whether lower molecular weight fibre provide the benefits of the high molecular weight fibres is therefore still unknown. Barley contains around 5 to 10% β-glucan fibre (compared to 4% in oats), which makes it an excellent source of β-glucan. However, more work is needed to understand its effects fully.
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