Abstract
BackgroundHigher dietary intake of fibers and coffee, but lower red meat intake is associated with reduced risk for type 2 diabetes in epidemiological studies. We hypothesized that a calorie-restricted diet, which is high in fiber and coffee, but free of red meat, improves beta-cell function in patients with T2D.MethodsIn a randomized parallel-group pilot trial, obese type 2 diabetes patients were randomly allocated to consume either a diet high in cereal fiber and coffee, but free of red meat (n = 17) (L-RISK) or a diet low in fiber, free of coffee but high in red meat (n = 20) (H-RISK) for 8 weeks. Insulin secretion was assessed from glucagon stimulation tests (GST) and mixed-meal tolerance tests (MMTT) before and after dietary intervention.ResultsBoth diets resulted in comparable reduction of fasting concentrations of insulin (H-RISK -28% vs. L-RISK -32%, bothp < 0.01), C-peptide (H-RISK -26% vs. L-RISK -30%, bothp < 0.01) and blood glucose (H-RISK -6.8%, p < 0.05 vs. L-RISK -10%, p < 0.01). Gastric inhibitory peptide (GIP) secretion increased by 24% after 8 weeks in the L-RISK only (p < 0.01). However, GST and MMTT showed no differences in insulin secretion after intervention.ConclusionsCalorie restriction independent of the intake of fiber, coffee or meat failed to improve beta-cell function, but improved GIP secretion in obese patients with type 2 diabetes.Trial registrationRegistration at Clinicaltrials.gov, Identifier number: NCT01409330, Registered 4 August 2011 – Retrospectively registered.
Highlights
Higher dietary intake of fibers and coffee, but lower red meat intake is associated with reduced risk for type 2 diabetes in epidemiological studies
While these studies tested the effects of single dietary modifications on metabolism, we recently reported on the comparison of two low-energy diets differing in coffee, fiber as well as red meat intake [23, 24]
Anthropometry Patients in both H-RISK and L-RISK groups did not differ in age, body mass index, glycemic control and lipidemia and had comparable blood glucose-lowering medications [23]
Summary
Patients and study design This study was performed in a subgroup of participants of a randomized controlled parallel group trial [23, 24], who underwent two additional tests for beta-cell function on two different days spaced by 8 weeks. All participants received individually calculated daily nutritional protocols, which they had to follow and were asked to document any changes. They had to return the completed sheets to monitor compliance. Glucagon stimulation test After overnight fasting for 12 h, blood samples were obtained for measurements of fasting glucose, insulin and C-peptide levels. Assuming that the two experimental samples follow Gaussian distribution, statistical significance of differences was assessed with the two-tailed t-test The effects of both diets on blood glucose and incretin levels and on parameters reflecting insulin secretion were analyzed by repeated measurement two-way ANOVA to compare diet-induced changes between groups as well as effects of time, diet and time - diet interaction. Analyses adjusted for BMI, weight loss and medication were performed to exclude these as confounding factors
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