Postprandial Glucose Response

After a meal, the extent of rise of blood glucose depends on several interacting factors. At the beginning of this century, scientists assumed that the molecular size of the carbohydrate was an important determinant of its rate of digestion. Starch was thus considered to be digested and absorbed slowly whereas low-molecular-weight carbohydrates were believed to be absorbed rapidly, hence promoting high responses of plasma glucose. Studies have since shown that food properties other than molecular size influence the postprandial response and that starchy foods can have glycemic indices ranging from low to high (25-27). Any process that disrupts the physical or botanical structure of food ingredients will increase the plasma glucose and insulin responses (28).

Consumption of foods with a high glycemic index and a low dietary fiber content has been listed among the causes of insulin resistance (29). Insulin resistance occurs when high blood concentrations of insulin do not decrease hyperglycemia efficiently. The extended hyperglycemic periods continue to stimulate insulin secretion. These conditions may lead to NIDDM (non-insulin-dependent-diabetes-melitus, or type II diabetes) (29).

According to Heaton (30), dietary fiber is generally resistant to digestion but its most important characteristic is that it constitutes the physical form and texture of whole foods. This structure affects several physiological phenomena: eating time, degree of satiety, rate of digestion, and extent of digestion. The presence of dietary fiber with an intact botanical structure prevents the high insuli-nemic peak following mastication and ingestion of an apple, and it also prevents the resulting hypoglycemia 2h after. The homogenization of the apple in apple puree destroys its botanical structure and largely reduces the beneficial physiological effects of the whole apple, even if its composition is not affected. The food macrostructure modulates the rate of digestion by digestive enzymes; it influences j the metabolic response to starchy foods (cereals, legumes) and to foods containing low-molecular-weight carbohydrates (apple, orange, carrot) (31-40). ^ Food structure is so important that the use of products with ''as fed'' food ^ structure has been recommended when measuring their glycemic index by en-zymic digestion to ensure a realistic result. Food structure must not be destroyed more than it would be by chewing (28).

Non-carbohydrate components significantly contribute to the cohesiveness of the botanical structure. Although the plant cell walls are largely made of carbohydrates, the structure has physiological effects unrelated to the carbohydrate components per se.

Mongeau et al.

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