Fibre supplementation for the prevention of type 2 diabetes and improvement of glucose metabolism: the randomised controlled Optimal Fibre Trial (OptiFiT)

Abstract

Aims/hypothesis Insoluble cereal fibres have been shown in large prospective cohort studies to be highly effective in preventing type 2 diabetes, but there is a lack of interventional data. Our 2 year randomised double-blind prospective intervention study compared the effect of an insoluble oat fibre extract with that of placebo on glucose metabolism and incidence of diabetes. Methods A total of 180 participants with impaired glucose tolerance underwent a modified version of the 1 year lifestyle training programme PREvention of DIAbetes Self-management (PREDIAS) and were randomised to receive a fibre supplement (n = 89; 7.5 g of insoluble fibre per serving) or placebo (n = 91; 0.8 g of insoluble fibre per serving) twice daily for 2 years. Eligible participants were men and women, were at least 18 years old and did not report corticosteroid or other intensive anti-inflammatory treatment, fibre intolerance or any of the following disorders: overt diabetes, chronic or malignant disease, or severe cardiopulmonary, endocrine, psychiatric, gastrointestinal, autoimmune or eating disorder. Participants were recruited at two clinical wards in Berlin and Nuthetal. The allocation was blinded to participants and study caregivers (physicians, dietitians, study nurses). Randomisation was conducted by non-clinical staff, providing neutrally numbered supplement tins. Both supplements were similar in their visual, olfactory and gustatory appearance. Intention-to-treat analysis was applied to all individuals. Results After 1 year, 2 h OGTT levels decreased significantly in both groups but without a significant difference between the groups (fibre −0.78 ± 1.88 mmol/l [p ≤ 0.001] vs placebo −0.46 ± 1.80 mmol/l [p = 0.020]; total difference 0.32 ± 0.29 mmol/l; Caroline Honsek and Stefan Kabisch contributed equally to this publication.Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00125-018-4582-6) contains peer-reviewed but unedited supplementary material, which is available to authorised users. not significant). The 2 year incidence of diabetes was 9/89 (fibre group) compared with 16/91 (placebo group; difference not significant). As secondary outcomes, the change in HbA 1c level was significantly different between the two groups (−0.2 ± 4.6 mmol/mol [−0.0 ± 0.0%; not significant] vs +1.2 ± 5.2 mmol/mol [+0.1 ± 0.0%; not significant]; total difference 1.4 ± 0.7 mmol/mol [0.1 + 0.0%]); p = 0.018); insulin sensitivity and hepatic insulin clearance increased in both groups. After 2 years, improved insulin sensitivity was still present in both groups, although the effect size had diminished. Separate analysis of the sexes revealed a significantly greater reduction in 2 h glucose levels for women in the fibre group (−0.88 ± 1.59 mmol/l [p ≤ 0.001] vs −0.22 ± 1.52 mmol/l [p = 0.311]; total difference 0.67 ± 0.31 mmol/l; p = 0.015). Levels of fasting glucose, adipokines and inflammatory markers remained unchanged in the two groups. Significantly increased fibre intake was restricted ...

High fiber intake, dietary protein, and prevention of type 2 diabetes

“…Notably, adverse effects of high protein intake on insulin sensitivity do not appear to apply in active people who relevantly stimulate also mTOR regulated increases in lean mass [3], which may compensate for proteinintake induced worsening of insulin resistance and is in line with the observation that in active athletes even very high protein intake does not appear to increase diabetes risk [3]. In addition, insoluble cereal fibers have been shown to alter the bile acid metabolic signature [15] and also may mechanically bind bile acids, thereby reducing cholesterol in plasma and restricting the absorption of dietary fats, which is beneficial for T2DM [8] The effectiveness of preventing T2DM by moderate alterations in lifestyle has been proven in two previous trials [referenced in [16]] and large epidemiological studies have identified insoluble cereal fibers as one of the most effective nutrient components for diabetes prevention [17]. However, relevantly increased fiber intake was not usually achieved.…”

“…The fiber supplements were purified fiber extracts derived from oat hulls, which contained 70% cellulose, 25% hemicellulose, and 3-5% lignin, to be dissolved in 300 mL water. Two out of three of the participants in the high cereal fiber group did reach their target for fiber intake [16] and increased cereal fiber intake indeed tended to reduce the incidence of T2DM over 2 years; and showed significant improvements in HbA1c and blood glucose concentrations over 1 year in women, despite otherwise identical lifestyle interventions in the placebo group [16]. Further, weight loss was almost non-existent at the end of the study and not different between the high-fiber and placebo groups, supporting the hypothesis that the observed beneficial metabolic effects of high insoluble cereal fiber intake were not linked to weight change [16].…”

“…Fiber intake may also help preventing diabetes by changing the gut microbiome [8], although the insoluble cereal fiber extracts that were used in our studies did not relevantly influence dominant groups of the gut microbiota [6]. Importantly, OptiFit also showed that long-term high cereal fiber intake can indeed be achieved in a sizable percentage of participants by the use of fiber extract supplements [16]. Insoluble cereal fibers are widely available by-products of flour production, generally show no gastrointestinal effects due to their non-fermentability [6,7], and could safely be added to various foods.…”

The Health Benefits of Dietary Fibre

“…There is much evidence in the literature to support an association between dietary fibre intake and insulin sensitivity [ 30 , 31 , 32 , 33 , 34 , 35 ]. Our own group published relevant evidence from an interventional trial using data from ProFiMet, the most highly-phenotyped cohort [ 36 ].…”

Association between dietary fibre intake and asthma (symptoms and control): results from the French national e-cohort NutriNet-Santé

“…Regarding inflammation, several epidemiological studies have reported that a greater intake of total fibre was associated with lower level of C-reactive protein (CRP) (50) and various proinflammatory cytokines such as lower plasma levels of TNF-α receptor 2 and IL-6 (51) . Consistently, a recent randomised controlled trial conducted by Honsek et al reported a decrease in CRP level after 1 year intervention with insoluble fibre supplementation or promoting healthy diet (including among others, an increase in fibre intake) (52) . In addition, in the recent pilot study by Halnes et al (20) , when comparing participants with stable asthma to the control group, a higher consumption of soluble fibre was associated with lower levels of sputum neutrophils, macrophages and lymphocytes.…”