Pierre Wursch

Physiological Effects of Resistant Starches on Fecal Bulk, Short Chain Fatty Acids, Blood Lipids and Glycemic Index

OBJECTIVE To assess the effects on fecal bulking, fecal short chain fatty acid (SCFA) production, blood lipids and glycemic indices of two different forms of resistant starch (RS2 and RS3) from a high-amylose cornstarch. METHODS Twenty-four healthy subjects (12 men; 12 women) consumed four supplements taken for 2 weeks in random order separated by 2-week washout periods. The supplements were a low-fiber (control) and supplements providing an additional 30 g dietary fiber as wheat bran (high-fiber control) or the equivalent amount of resistant starch analyzed gravimetrically as dietary fiber from RS2 or RS3. Four-day fecal collections and 12-hour breath gas collections were obtained at the end of each period. Fasting blood was taken at the beginning and end of each period. Glycemic indices of supplements were also assessed. RESULTS The wheat bran supplement increased fecal bulk 96+/-14 g/day compared with the low-fiber control (p<0.001) with the mean for both resistant starches also being greater (22+/-8 g/day) than the low-fiber control (p=0.013). On the resistant starch phases, the mean fecal butyrate:SCFA ratio, which has been suggested to have positive implications for colonic health, was significantly above the low-fiber control by 31+/-14% (p=0.035). Resistant starches did not alter serum lipids, urea or breath H2 or CH4. No significant differences in glycemic index were seen between the RS and control supplements. CONCLUSION The potential physiological benefits of the resistant starches studied appear to relate to colonic health in terms of effects on fecal bulk and SCFA metabolism.

Inhibition of amylopectin retrogradation by partial beta-amylolysis

The rate of retrogradation of amylopectin solution differs from one starch variety to another and it is thought to be due to the different length of the external chains of amylopectin. A shortening of the external chains of waxy maize and potato amylopectin was performed with beta-amylase. Partial beta-amylolysis produced a significant fraction of chains having 2-6 glucose units. A high linear correlation (R > 0.97) was found between the enthalpy of retrograded amylopectin measured by DSC, or percent solid measured by low frequency pulsed NMR, and average external chain length. No retrogradation appeared to occur when the external chains of both amylopectins had 11 or less glucose units on average. The inhibition of retrogradation appears to be caused primarily by the presence of very short external chains, which hinders the reassociation of the long external chains.

Comparison of Metabolic Effects of White Beans Processed Into Two Different Physical Forms

In the present study eight control subjects and eight patients with non-insulin-dependent diabetes mellitus (NIDDM) consumed single portions of processed beans equivalent to 50 g of carbohydrate. The beans were processed by different methods into two physical forms; one maintained the integrity of the bean cells (undamaged bean cells, UC) and the other ruptured the bean cells (damaged bean cells, DC). Incremental glucose response areas after ingestion of either UC or DC were not significantly different in control subjects, while incremental insulin response areas (49 ± 7 vs. 26 ± 4 μU · ml−1 · h−1 P < .05) were significantly lower after eating UC-processed beans. In patients with NIDDM both incremental glucose (150 ± 14 vs. 73 ± 25 mg · dl−1 · h - 1 ,P < .001) and insulin (67 ± 16 vs. 46 ± 11 μU · ml−1 · h−1 P < .05) response areas were significantly lower after UC administration. To test the effectiveness of the UC-processed bean when incorporated into mixed meals, nine patients with NIDDM consumed mixed meals containing either DC or UC on two separate mornings. The test meals represented a typical Mexican American use of pureed beans wrapped in a flour tortilla topped with melted cheese. Incremental glucose responses were significantly lower after the UC meal (171 ± 42 mg · dl−1 · h−1 P < .05) when compared with the DC meal (212 ± 34 mg · dl−1 · h−1). Incremental insulin areas were also lower after the UC (91 ± 19 μU · ml−1 · h−1) when compared with the DC meal (120 ± 22 μU · ml−1 · h−1). Our study demonstrates that consumption of white beans prepared in a manner that maintains the integrity of the cells profoundly modified the ensuing plasma glucose and insulin response in patients with NIDDM as compared with white beans milled in a more conventional fashion. Moreover, the lower glucose and insulin response to UC beans occurred when the beans were consumed alone or in a mixed meal and suggests that the practice of processing carbohydrate-rich foods in a manner that leaves the food form intact may be of significant clinical importance.

The effect of muesli or cornflakes at breakfast on carbohydrate metabolism in type 2 diabetic patients

Fourteen overweight insulin-treated type 2 diabetic patients ate a breakfast, consisting of either muesli (slow release starch: SRS) or cornflakes (fast release starch: FRS), in either case with milk (46 g carbohydrate), during two consecutive randomized crossover periods of two weeks. The rest of the diet remained unchanged. At the end of each period the patients underwent a glucose tolerance test after an overnight fast without their usual evening insulin injection. Both mean plasma glucose responses curves were identical after the two dietary periods, but plasma insulin was significantly lower at zero (-17%, P less than 0.05) and 2 h (-21%, P less than 0.05) at the end of the muesli (SRS) period as compared to the cornflakes (FRS) period. The mean day-long plasma glucose level (four measurements) at the end of the muesli period was 21% (P = 0.023) lower than after the cornflakes period. These results show that switching, at breakfast only, from standard cereals to slow release starch cereals improves the carbohydrate metabolism of diabetic patients. In addition, the fact that diabetic patients could reduce their insulin requirement (P less than 0.05) with concomitant reduction of their daily blood glucose level implies that sensitivity to insulin was improved by slow release starct foods consumed at breakfast.

Colonic bacterial activity and serum lipid risk factors for cardiovascular disease.

Antibiotics are being proposed for the treatment of cardiovascular disease. In the past, antibiotics were advocated for the control of hypercholesterolemia. We have therefore investigated the relation between colonic bacterial activity and serum lipids. In a four-phase randomized crossover study, we fed a different starch supplement during each 2-week phase to 24 healthy subjects. In two phases, supplements containing resistant starches were fed that reach the colon and are largely fermented by colonic bacteria. Fecal starch recovery therefore reflects the metabolic activity of colonic microflora. The control treatments were conventional starches. Blood lipid levels were obtained at the start and 4-day fecal collections at the end of each phase. Resistant starch supplements increased fecal starch excretion by 3.8 +/- 1.2 g/d more than conventional starches (P = .006). Mean starch excretion was related positively to pretreatment serum high-density lipoprotein (HDL) cholesterol (r = -.57, P = .003) and negatively to low-density lipoprotein (LDL) cholesterol (r = -.57, P = .004), apolipoprotein B:AI (r = -.56, P = .005), and fecal output of fusobacteria (r = -.73, P = .003) and bacteroides (r = -.72, P = .003). The ratio of fusobacteria to total anaerobes was also related to pretreatment LDL cholesterol (r = .56, P = .037). Differences in starch excretion between healthy subjects, as a measure of bacterial activity, accounted for 32% of the variation in pretreatment LDL cholesterol. The activity of colonic microflora therefore appears to influence serum lipid levels. Alterations of bacterial number and activity may provide an additional strategy to control serum lipid risk factors for cardiovascular disease.

Maltotriitol Inhibition of Maltose Metabolism in Streptococcus mutans via Maltose Transport, Amylomaltase and Phospho-α-Glucosidase Activities

Maltose glycolysis and transport in Streptococcus mutans OMZ 176 were shown to be inhibited by maltotriitol (MTL). The sugar alcohol was taken up, but was not metabolized. The phosphoenolpyruvate: maltose phosphotransferase (PEP:PTS) system activity was present in cells grown on glucose and maltose and was not inhibited by MTL. The product of the maltose PTS reaction was isolated and identified as maltose 6′-phosphate. The phospho-α-glucosidase induced by maltose hydrolyzed maltose phosphate into glucose and glucose 6-phosphate. The maltose-inducible amylomaltase which catalyses the transfer of both glucosyl and maltodextrinyl units was purified. The apparent Km for maltose was 21.8 mM. MTL inhibited the enzyme activity on maltose (Ki 2.0 mM) and maltotriose without being itself a substrate, but transglycosylation occurred on MTL when maltoheptaose was the donor substrate. These results indicated that in strain OMZ 176, maltose transport was mediated by a PEP-dependent maltose PTS yielding maltose 6′-phosphate which subsequently was hydrolyzed by a maltose-inducible phospho-α-glucosidase. It was suggested that MTL inhibits glycolysis of maltose by reducing the rate of maltose transport and inhibiting amylomaltase and phospho-α-glucosidase activities, resulting in an accumulation of maltose 6′-phosphate.

Metabolism of L-Sorbose in the Rat and the Effect of the Intestinal Microflora on its Utilization Both in the Rat and in the Human

L-[U-14C]-sorbose was administered orally as single doses to 5 normal rats. The recovery of radioactivity was 5.3% in the urine, 46% in the faeces exclusively as L-sorbose 16% as carbon dioxide. Caloric utilization was approximately 25%. A second group of 3 rats that had previously received L-sorbose in their diet showed 14C recoveries of 8.9% in the urine, 6.6% in the faeces and 59% as carbon dioxide. The time course of expired carbon dioxide suggests that a portion of L-sorbose was rapidly absorbed and partially metabolized while the principal pathway involved fermentation by the intestinal microflora to volatile fatty acids which were subsequently absorbed and metabolized. The total caloric utilization of L-sorbose was estimated to be 70%. It was observed that a human intestinal microflora also required an adaptation period in order to ferment this sugar. The efficiency of the fermentation was estimated to be 70%.