Obesity Does Not Modulate the Glycometabolic Benefit of Insoluble Cereal Fibre in Subjects with Prediabetes—A Stratified Post Hoc Analysis of the Optimal Fibre Trial (OptiFiT)

Abstract

Obesity does not modulate the glycometabolic benefit of insoluble cereal fibre in subjects with prediabetes—a stratified post hoc analysis of the Optimal Fibre Trial (OptiFiT). Background: OptiFiT demonstrated the beneficial effect of insoluble oat fibres on dysglycemia in prediabetes. Recent analyses of OptiFiT and other randomised controlled trials (RCTs) indicated that this effect might be specific for the subgroup of patients with impaired fasting glucose (IFG). As subjects with IFG are more often obese, there is a need to clarify if the effect modulation is actually driven by glycemic state or body mass index (BMI). Aim: We conducted a stratified post hoc analysis of OptiFiT based on the presence or absence of obesity. Methods: 180 Caucasian participants with impaired glucose tolerance (IGT) were randomised in a double-blinded fashion to either twice-a-day fibre or placebo supplementation for 2 years (n = 89 and 91, respectively). Once a year, they underwent fasting blood sampling, an oral glucose tolerance test (oGTT) and full anthropometry. At baseline, out of 136 subjects who completed the first year of intervention, 87 (62%) were classified as OBESE (BMI >30) and 49 subjects were NONOBESE. We performed a stratified per-protocol analysis of the primary glycemic and secondary metabolic effects attributable to dietary fibre supplementation after 1 year of intervention. Results: Neither the NONOBESE nor the OBESE subgroup showed significant differences between the respective fibre and placebo groups in metabolic, anthropometric or inflammatory outcomes. None of the four subgroups showed a significant improvement in either fasting glucose or glycated haemoglobin (HbA1c) after 1 year of intervention and only OBESE fibre subjects improved 2 h glucose. Within the NONOBESE stratum, there were no significant differences in the change of primary or secondary metabolic parameters between the fibre and placebo arms. We found a significant interaction effect for leukocyte count (time × supplement × obesity status). Within the OBESE stratum, leukocyte count and gamma-glutamyl transferase (GGT) levels decreased more in the fibre group compared with placebo (adjusted for change in body weight). Comparison of both fibre groups revealed that OBESE subjects had a significantly stronger benefit with respect to leukocyte count and fasting C-peptide levels than NONOBESE participants. Only the effect on leukocyte count survived correction for multiple comparisons. In contrast, under placebo conditions, NONOBESE subjects managed to decrease their body fat content significantly more than OBESE ones. Intention-to-treat (ITT) analysis resulted in similar outcomes. Conclusions: The state of obesity does not relevantly modulate the beneficial effect of cereal fibre on major glycometabolic parameters by fibre supplementation, but leukocyte levels may be affected. Hence, BMI is not a suitable parameter to stratify this cohort with respect to diabetes risk or responsiveness to cereal fibre, but obesity needs to be accounted for when asse...

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 ].…”

“…Finally, in a recent systematic review and meta-analysis on the effects of dietary fibre and whole grains in the management of Diabetes Mellitus, there was an association of high-fibre diet with improved insulin sensitivity, including many other aspects of metabolic health, such as HbA1C, lipid profile, body weight and C-reactive protein [ 39 ]. There is, however, a deficiency of published longer-term controlled studies (>12 months) on the metabolic effects of increasing dietary fibre intake [ 39 ] (with a notable exception [ 35 ]), and this should be a focus for future research in this field.…”

“…In this study, given the association of dietary fibre intake with body fat percentage, it is possible that the favourable effects of dietary fibre on inflammatory status (indicated by plasma level of CRP) are actually mediated, at least in part, by changes in body composition rather than a direct effect of dietary fibre. In a further study, Kabisch and colleagues demonstrated an interventional interaction effect of dietary fibre supplementation on inflammation [ 35 ]. Interestingly, whilst the effect size for the anti-hyperglycaemic properties of insoluble dietary fibre seemed to depend mainly on the prevailing metabolic state, the anti-inflammatory effect of the particular supplement used in this study related primarily to the presence or absence of obesity [ 35 ].…”

“…In a further study, Kabisch and colleagues demonstrated an interventional interaction effect of dietary fibre supplementation on inflammation [ 35 ]. Interestingly, whilst the effect size for the anti-hyperglycaemic properties of insoluble dietary fibre seemed to depend mainly on the prevailing metabolic state, the anti-inflammatory effect of the particular supplement used in this study related primarily to the presence or absence of obesity [ 35 ].…”

“…There is corroboration of this conclusion by reported data from studies on dietary fibre. For example, in our own interventional OptiFiT study, the control group was encouraged to eat more fibre with little success [ 34 , 35 ]. An alternate strategy would be for the food industries to produce healthy processed foods that are rich in dietary fibre.…”