Showing papers by "Thomas M.S. Wolever published in 1990"

The glycemic index.

Abstract: Different starchy foods produce different glycemic responses when fed individually, and there is evidence that this also applies in the context of the mixed meal Methods of processing, and other factors unrelated to the nutrient composition of foods may also have major effects on the glycemic response The reason for differences in glycemic response appears to relate to the rate at which the foods are digested and the many factors influencing this The glycemic index (GI) is a system of classification in which the glycemic responses of foods are indexed against a standard (white bread) This allows the results of different investigators to be pooled GI values also depend upon a number of nonfood-related variables The method of calculation of the glycemic response area is most important, but the method of blood sampling and length of time of studies also may have effects Variability of glycemic responses arises from day-to-day variation in the same subject and variation between different subjects There is less variability between the GI values of different subjects than there is within the same subject from day to day Therefore, the mean GI values of foods are independent of the glucose tolerance status of the subjects being tested Potentially clinically useful starchy foods producing relatively flat glycemic responses have been identified, including legumes, pasta, barley, bulgur, parboiled rice and whole grain breads such as pumpernickel Specific incorporation of these foods into diets have been associated with reduced blood glucose, insulin, and lipid levels Low-GI foods may influence amino acid metabolism although the implications of these are unknown In addition, low GI foods increase colonic fermentation The physiologic and metabolic implications of this relate to increased bacterial urea utilization, and to the production and absorption of short chain fatty acids in the colon The application of the GI to therapeutic diets should be in the context of the overall nutrient composition of the diet High-fat or high-sugar foods may have a low GI, but it may not be prudent to recommend these foods solely on the basis of the GI It is therefore suggested that the most appropriate use of the GI is to rank the glycemic effects of starchy foods which would already have been chosen for possible inclusion in the diet on the basis of their nutritional attributes, ie low-fat, unrefined carbohydrate

Metabolic effects of reducing rate of glucose ingestion by single bolus versus continuous sipping.

Abstract: Modifying the rate of absorption has been proposed as a therapeutic principle of specific relevance to diabetes. To demonstrate clearly the metabolic benefits that might result from reducing the rate of nutrient delivery, nine healthy volunteers took 50 g glucose in 700 ml water on two occasions: over 5-10 min (bolus) and at a constant rate over 3.5 h (sipping). Despite similar 4-h blood glucose areas, large reductions were seen in serum insulin (54 +/- 10%, P less than 0.001) and C-peptide (47 +/- 12%, P less than 0.01) areas after sipping, together with lower gastric inhibitory polypeptide and enteroglucagon levels and urinary catecholamine output. There was also prolonged suppression of plasma glucagon, growth hormone, and free-fatty acid (FFA) levels after sipping, whereas these levels rose 3-4 h after the glucose bolus. An intravenous glucose tolerance test at 4 h demonstrated a 48 +/- 10% (P less than 0.01) more rapid decline in blood glucose (Kg) after sipping than after the bolus. Furthermore, FFA and total branched-chain amino acid levels as additional markers of insulin action were lower over this period despite similar absolute levels of insulin and C-peptide. These findings indicate that prolonging the rate of glucose absorption enhances insulin economy and glucose disposal.

Glycemic Index of Foods in Individual Subjects

Abstract: We studied 12 subjects with diabetes to determine how well the glycemic index (GI) predicted the ranking of glycemic responses of different foods in individuals. All subjects ate three mixed meals (bread, rice, or spaghetti with GIs of 100, 79, and 61, respectively) four times in a randomized complete block design. The mean glycemic response areas of the different meals ranked according to the predicted GI in every individual. The observed mean +/- SD GI values of the meals were significantly different from each other (bread 100 +/- 7, rice 75 +/- 9, spaghetti 54 +/- 9), with no significant difference in response between subjects. It is concluded that individuals share common mean GI values for different foods. Within confidence limits determined by the variability of glycemic responses, the number of repeated tests conducted, and the expected GI difference, the GI can be used to predict the ranking of the mean glycemic responses of mixed meals taken by individuals.

Metabolic effects of continuous feeding.

Abstract: To study the metabolic effects of slowing absorption, as a possible mechanism for the blood glucose and lipid-lowering effects of soluble fiber and low glycemic index (GI) foods, seven healthy men consumed a liquid formula diet either as three equal meals at 4-hour intervals, or by continuously sipping the same amount of formula over the 12-hour study period. Meal-related fluctuations of blood glucose, insulin, and triglycerides were seen during three meals, but not during sipping. Mean 12-hour levels of blood glucose and beta-hydroxybutyrate (beta OHB) were equivalent on sipping and three meals. The total integrated insulin area was reduced by 32% on sipping (P less than .01), but this was not explained by the 16% (NS) reduction in serum C-peptide response. Mean serum free fatty acid (FFA) and cholesterol levels were reduced by 20% and 2.6%, respectively (P less than .01). It is concluded that the reduced glycemic responses seen after soluble fiber-enriched meals and low GI foods can be explained by slow absorption. Although the overall mean daily blood glucose levels may not be reduced by slowing carbohydrate absorption in nondiabetic subjects, this is achieved at considerably lower ambient serum insulin concentrations. The reduction of insulin levels may be an important mechanism for the serum cholesterol-lowering effect of soluble fiber and low GI foods.

Dietary fiber in the Management of Diabetes

Abstract: Over the past two decades there has been a radical change in dietary guidelines for diabetes, which now stress high carbohydrate and fiber intakes. The initial impetus for the increase in carbohydrate came from early studies of Himsworth (1935–36) and, later, Stone and Connor (1965), showing improved blood lipids and glucose tolerance on a high-carbohydrate diet. Further motivation for change originated in the early 1970s from Trowell’s suggestion (1973) that the development of diabetes might be related to a lack of fiber in the diet. This spurred many new concepts about the dietary treatment of diabetes and lead to the classic studies of Anderson (Kiehm et al., 1976; Anderson and Ward, 1979) and others (Simpson et al., 1981; Rivellese et al., 1980) showing the beneficial effects of high-carbohydrate, high-fiber diets.

Fiber and physiological and potentially therapeutic effects of slowing carbohydrate absorption.

Abstract: The dietary recommendations of diabetes associations, heart foundations, and cancer agencies encourage the use of higher carbohydrate intakes derived from minimally processed or high fiber foods (1–5). A characteristic of such foods is often that they are more slowly absorbed than many refined and highly processed foods. The assumption that slow absorption of nutrients is of benefit is central to the original fiber hypothesis (6) and has been described as a new therapeutic principle (7). Fibers that have proved especially useful include the soluble fibers. Early on purified soluble fibers such as guar and pectin were found to be particularly useful in lowering cholesterol in patients at high risk of heart disease (8,9). This paved the way for current interest in high soluble fiber foods such as beans, oats (e.g. oat bran), barley, etc., all of which have been shown to have these effects (10). Our own current interest has been in the use of traditional starchy foods, e.g. beans, dried peas, lentils, barley, etc., or starchy foods processed in traditional ways, e.g. pumpernickel bread (whole kernel rye), bulgur (cracked parboiled wheat), pasta, etc. These foods reduce serum cholesterol in patients at risk of heart disease and also provide better blood glucose control in patients with diabetes. There is also evidence that they may be of benefit in liver disease and in kidney disease because of their effects on amino acid and nitrogen metabolism. A growing body of evidence suggests that many traditionally processed foods, especially those still eaten in parts of the world where heart disease, diabetes and colonic diseases are rare, may owe much to the fact that their carbohydrate, possibly due to fiber content, is more slowly absorbed. Other means by which these same effects can be produced include the use of specific digestive enzyme inhibitors and increased feeding frequency.

Lente Carbohydrate or Slowly Absorbed Starch

Abstract: Current dietary recommendations support the use of increased carbohydrate intakes from minimally processed or high-fiber starchy foods. A characteristic of such food is often that it is more slowly digested and absorbed than many refined and highly processed foods. The assumption that slow absorption of nutrients may have benefit is central to the fiber hypothesis and has been described as a new therapeutic principle. Other similar approaches include the use of specific digestive enzyme inhibitors and increased feeding frequency. Slow carbohydrate absorption may result in a number of sequelae, including flatter glucose and endocrine responses and lower blood lipids, reduced blood urea levels through increased NH3 trapping in the colon, increased laxation, and enhanced colonic retrieval of short-chain fatty acids with further potential beneficial effects.