Effects of dietary fibre on the human metabolism and metabolome

It is well-known that dietary fibre can have a positive effect on the development of lifestyle-dependent diseases such as cardiovascular disease and type 2 diabetes. However, the effect may be different for different kinds of fibre and different sub-populations at risk. Therefore, the effects of three different kinds of fibre on postprandial and long-term response in healthy subjects were investigated. Consumption of rye bran, oat powder, sugar beet fibre or a mixture of all three in a meal study, led to lower postprandial glucose levels for all meals except oat powder, although the difference was only significant for rye bran. The outcome seemed to be determined not only by the amount of soluble fibre, but also by the total dietary fibre content. The combined effect of an intake of oat bran, rye bran and sugar beet fibre was also investigated in a 5-week randomised cross-over intervention study in healthy, mildly hypercholesterolaemic subjects. Subjects were given a high-fibre (HF) diet (48 g) and a low-fibre (LF) diet (30 g). Despite the high fibre intake, no significant effects were observed on glucose, insulin, or lipid metabolism. However, low-grade inflammatory response was reduced by the HF diet, as reflected by decreased C-reactive protein and fibrinogen levels. Moreover, markers from the high intake of oat, rye and sugar beet fibre were observed in plasma and 24-h urine samples using an untargeted metabolomic profiling approach. After the HF diet, different benzoxazinoids and their metabolites 2-aminophenol sulphate, HPAA (N-(2-hydroxyphenyl)acetamide) and HHPAA (2-hydroxy-N-(2-hydroxyphenyl)acetamide), together with the alkylresorcinol metabolite DHPPA (3-(3,5-dihydroxyphenyl)-1-propanoic acid), were found to be specific for the rye intake, whereas enterolactone was related to rye and oat fibre intake. Some specific markers for oat intake were found, however, their identity needs further validation. One identified marker, 2,6-DHBA (dihydroxybenzoic acid), has not previously been reported as a marker related to dietary fibre intake. Whether there is a specific marker for sugar beet fibre intake remains unclear. These markers of the intake of specific dietary fibre sources could, if validated, serve as markers in intervention studies and larger observational studies, to provide more accurate data on general dietary fibre intake, apart from the subjects’ self-reported values, which are normally used. The effect of a healthy Nordic diet based on the Nordic Nutrition Recommendations, including a high dietary fibre intake, was investigated in obese subjects with metabolic syndrome. This was a randomised, parallel multi-centre study in which the Nordic diet was compared to a control diet. No effects were observed on the glucose and insulin metabolism, however, reductions in lipoproteins were found together with an indication of reduction in the inflammatory response after the intake of the Nordic diet. In conclusion, these studies confirm that a high dietary fibre intake has a beneficial effect on glucose and lipid metabolism. The intervention studies also indicated a reduction in low-grade inflammation markers that are associated with overweight and type 2 diabetes.