Amylose and amylopectin are polysaccharides found in varying ratios between different carbohydrate foods. Amylose is composed of straight chains of D-glucose molecules linked by α-(1-4) bond, whereas amylopectin has a branched structure that comprises of D-glucose linked by α-(1-4) and α-(1-6) linkages. Most starches contain around 20 to 35 % amylose but some starch sources have considerably higher amounts. Some strains of maize for example may contain up to 70 % amylose. The amylose to amylopectin ratio of starch in foods is important because it affects the digestion rate and therefore the subsequent physiological parameter. Generally, goods higher in amylose are digested more slowly because the linear structure decreases the rate that the glucose can be hydrolysed from the structure, compared to the branched structure of amylopectin. Evidence suggests that foods with a high amylose to amylopectin ratio may decrease insulin release and blood glucose levels following a meal.
For example, researchers1 have investigated the effects of altering the amylose to amylopectin ratio of a corn meal on 22 normal weight healthy volunteers. The corn was fed at breakfast and lunch, with breakfast consisting of a corn baguette, and lunch consisting of a pizza, both containing either a high amylose or a low amylose content. Blood samples were taken to assess the insulin and glucose concentrations of the plasma and a hydrogen breath test was used to assess the fermentation of starch in the colon. The results showed that following breakfast, there was no significant difference between the blood glucose levels or blood insulin levels following ingestion of the high amylose or low amylose baguette, but glycerol area under the curve was reduced. Following lunch blood glucose levels were significantly lower for the high amylose pizza compared to the low amylose pizza, and total areas under the curve for both insulin and glucose were reduced significantly.
The amylose content of the meals had no effects on hunger or satiety and the subjects reported that the food were equally appealing. The appeal of the foods was important to report in this study because high amylose foods are often not palatable following heating because amylose does not gelatinise to the same degree as amylopectin. Breath hydrogen values were not significantly different unit 7 hours after the food was ingested, at which point the high amylose meals produced significantly higher amounts of hydrogen. This suggests that digestion rates were reduced and the amylose was being fermented at a higher rate by colonic microflora. This would explain the lower insulin and glucose response following the high amylose meals. The lack of effects of the breakfast on glucose and insulin levels may relate to the energy content of the foods or the macronutrient profiles, which were different between breakfast and lunch. The larger meal size at lunch may explain why the results became significant for lunch.
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