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The incidence of diabetes is increasing alarmingly indicating a need for preventive strategies. Prospective evidence is inconclusive regarding the protective effect of high fibre intake on the risk of Type 2 diabetes mellitus (T2DM). Differences in fibre measuring methodologies may have contributed some of these inconsistencies. For the first time, this thesis employed both laboratory and epidemiological approaches to explore different aspects of dietary fibre. Firstly, 14 commonly consumed legumes were analysed for fibre content using the Association of Official Analytical Chemists (AOAC) method, and the values were significantly higher than published non-starch polysaccharide (NSP) values, with a mean AOAC-fibre: NSP ratio of 1:1.43. The UK Women’s Cohort Study (UKWCS) data was used to compare AOAC-fibre intakes with NSP intakes. Good agreement (Kappa = 0.9) was observed between intakes of AOAC-fibre and NSP with a resulting AOAC-fibre: NSP ratio being generated of 1:1.43. Following this, the links between risk of incident T2DM and intakes of AOAC-fibre and NSP were investigated. There was no evidence of dose-response relationships between T2DM risk and total fibre intake (AOAC-fibre and NSP) or from key fibre sources, except an age-adjusted lower risk of T2DM with every 5g/day increment in cereal fibre (OR=0.86; 95%CI: 0.75, 0.99). As an important fibre provider; the relationship between the risk of T2DM and legume consumption was also explored. Women in the highest dried legumes intake category experienced significantly lower odds of incident T2DM (OR=0.85; 95%:0.52, 0.89, p =0.03) compared to women in the lowest category. Agreement of fibre intake obtained using different dietary assessments approaches suggested fair agreement of diary derived NSP vs. FFQ derived NSP and poor agreement for vegetable fibre. Overall, results do not support an increase in fibre intake to prevent diabetes in the studied population, although there may be a benefit of increased dried legume intake.