Physical factors Influencing postprandial glucose and insulin responses to starch

Abstract

The present study was undertaken to gain further insight into the roles of physical form and fiber in determining postprandial glucose and insulin responses to orally ingested, cooked starch. The starch was consumed as rice, either white (polished, ground, or unground) or brown (unpolished, ground, or unground). Each carbohydrate load was calculated to contain the equivalent of 75 g glucose. Both ground rice meals elicited much higher peak responses of glucose and insulin than either of the unground samples. This seemed to be due to the more rapid absorption of the ground rice since the area under the glucose curve during the first 60 min was higher for ground rice than for unground rice, irrespective of whether or not it was polished. However, the full 240 min glucose areas were similar for all four forms of rice suggesting that the early differences were due to different rates of absorption. The presence of fiber had little discernible effect on the overall glucose and insulin responses, since brown rice did not elicit a significantly lower glucose or insulin response than white rice. However, there was a sustained and significant increase in insulin secretion in response to ground compared with unground rice. It was concluded that the physical form of the rice was of particular importance in determining the postprandial glucose and insulin responses to rice and that fiber, per se, played a relatively minor role in this instance. Any factor (low surface area/starch ratio in this case) that limits access of the intestinal hydrolytic enzymes to the ingested starch would be expected to slow the rate of glucose absorption and thereby reduce the insulin secretion.