Impact of short term consumption of diets high in either non-starch polysaccharides or resistant starch in comparison with moderate weight loss on indices of insulin sensitivity in subjects with metabolic syndrome

Abstract

This study investigated if additional non-starch polysaccharide (NSP) or resistant starch (RS), above that currently recommended, leads to better improvement in insulin sensitivity (IS) than observed with modest weight loss (WL). Obese male volunteers (n = 14) were given an energy-maintenance (M) diet containing 27 g NSP and 5 g RS daily for one week. They then received, in a cross-over design, energy-maintenance intakes of either an NSP-enriched diet (42 g NSP, 2.5 g RS) or an RS-enriched diet (16 g NSP, 25 g RS), each for three weeks. Finally, a high protein (30% calories) WL diet was provided at 8 MJ/day for three weeks. During each dietary intervention, endogenous glucose production (EGP) and IS were assessed. Fasting glycaemia was unaltered by diet, but plasma insulin and C-peptide both decreased with the WL diet (p < 0.001), as did EGP (-11%, p = 0.006). Homeostatis model assessment of insulin resistance improved following both WL (p < 0.001) and RS (p < 0.05) diets. Peripheral tissue IS improved only with WL (57%-83%, p < 0.005). Inclusion of additional RS or NSP above amounts currently recommended resulted in little or no improvement in glycaemic control, whereas moderate WL (approximately 3 kg fat) improved IS.

Figure 1

Time line (min) of the various infusions on the last day of each dietary period. The vertical dashes on the time line indicate sampling points. The [1-¹³C]leucine and [6,6-²H₂]glucose were infused at tracer amounts, while the dextrose infusion represents a 75 g glucose challenge infused over 2 h. Insulin was injected at 0.04 IU/kg body weight (BW) at 60 min after start of dextrose infusion.

Figure 2

Three compartment model to describe transfers from a primary pool (A) to either a readily accessible (B) or less-readily accessible (C) pool. Values obtained from 14 volunteers with each measured on just one occasion in the overnight fasted state. Subjects were injected intravenously with a bolus dose of [U-¹³C]glucose and blood samples taken at intervals over 150 min. A three compartment model was fitted to the TTR of plasma glucose. Values in parentheses include all volunteers, other values exclude two volunteers for whom inadequate model fits were obtained. Values beside arrows are fractional rate constants (min⁻¹).

Figure 3

Comparison of calculated endogenous glucose production (EGP) based on either the Simple model, that allows for return of label to primary pool, or assuming steady state, where no allowance for label return is included. Data from the M diet, but the other diets gave similar patterns (not shown). The difference in calculated EGP at time 0 is because the Simple model allowed for the slow decline in plasma glycaemia during the 2 h fasting prior to the dextrose challenge. Differences in the decline and recovery of EGP over time again reflect that the Simple model allows for the return of label to the plasma pool while the steady state approach does not.