Plasma glucose and insulin reduction after consumption of breads varying in amylose content.

OBJECTIVE: Consumption of a meal high in amylose starch (70%) decreases peak insulin and glucose levels and area under the curve (AUC). The objective was to determine the amount of amylose necessary in a meal for the beneficial decrease in glucose or insulin to occur. DESIGN: Twenty-five subjects, 13 men (averaging 88.1 kg, 41 y, and 27.9 body mass index) and 12 women (averaging 72.4 kg, 41 y and 27.1 body mass index) were given six tolerance tests in a Latin Square design: glucose alone (1 g glucose/kg body weight) and five breads (1 g carbohydrate/kg body weight) made with 70% amylose cornstarch, standard cornstarch (30% amylose), and blends of the two starches (40, 50 and 60% amylose starch). A standard menu was fed for 3 days. One subject withdrew from the study. RESULTS: Glucose, insulin and glucagon response to the carbohydrate loads was similar in men and women. Peak glucose response was lowest after the breads containing 50-70% amylose starch. AUC was significantly higher after the glucose load than after all bread loads. The lowest AUCs occurred after the 60 and 70% amylose starch breads. Insulin response and AUC were significantly lower after the 60 and 70% amylose starch breads than after the glucose or the other breads. CONCLUSION: Results indicate that the amylose content of the starch used in the acute meal needs to be greater than 50% to significantly reduce plasma glucose and insulin in men and women.

Mechanisms of the effects of grains on insulin and glucose responses.

Consumption of a number of grains and grain extracts has been reported to control or improve glucose tolerance and reduce insulin resistance. The inability of the body to maintain normal glucose levels or to require excessive levels of insulin to do so has been called glucose intolerance, impaired glucose tolerance and insulin resistance. These conditions are associated with obesity and may be preliminary steps in the progression to type 2 diabetes mellitus. Although dietary goals recommend the consumption of three servings of whole grains per day, average consumption in the United States is less than one serving per day. There are a number of mechanisms by which grains may improve glucose metabolism and delay or prevent the progression of impaired glucose tolerance to insulin resistance and diabetes. These mechanisms are related to the physical properties and structure of grains. The composition of the grain, including particle size, amount and type of fiber, viscosity, amylose and amylopectin content all affect the metabolism of carbohydrates from grains. Increasing whole grain intake in the population can result in improved glucose metabolism and delay or reduce the risk of developing type 2 diabetes mellitus. Whole grains can provide a substantial contribution to the improvement of the diets of Americans. A number of whole grain foods and grain fiber sources are beneficial in reduction of insulin resistance and improvement in glucose tolerance. Form, amount and method of cooking of these foods as well as the health characteristics, age and gender of the group of subjects studied are all important factors in the effectiveness of the foods in altering these responses. Dietary recommendations of health organizations suggest consumption of three servings a day of whole grain foods; however, Americans generally fall below this standard. Recent research using various grains and grain products effective in improving insulin resistance or lowering glycemic index will be discussed below by possible mechanisms of action.

The effect of particle size of whole-grain flour on plasma glucose, insulin, glucagon and thyroid-stimulating hormone in humans.

OBJECTIVE: Although it is well known that consumption of whole-grain foods with higher fiber content results in beneficial health effects, most Americans usually prefer bread made with white flour. Changes in bread texture and undesirable intestinal responses have been reported as reasons for avoiding consumption of whole-grain foods or high-fiber menus. The purpose of this study was to determine whether consumption of bread made with ultra-fine-ground whole-grain wheat flour retained beneficial effects while reducing undesirable effects. METHODS: Twenty-six men and women, 31 to 55 years of age, consumed glucose solutions or bread made with traditional white, conventional whole-grain wheat (WWF), or ultra-fine whole-grain wheat (UFWF) flour (1 g carbohydrate/kg body weight) in a Latin square design after two days of controlled diet. The effect on glycemic response was determined by comparing blood variables, after a tolerance test with white bread, WWF bread, and UFWF bread, with those after a glucose tolerance test. RESULTS: Men and women had similar responses to all tolerances except postprandial TSH. Glucose and insulin levels one half hour after the glucose load were significantly higher than after any of the bread tolerances. Glucose, but not insulin, areas under the curve were significantly higher after the glucose load than areas after the three breads. Consumption of UFWF resulted in glucose and insulin responses, as well as areas under the curve, similar to those after consumption of conventional whole-wheat bread. CONCLUSION: The particle size of whole grain wheat flour did not substantially affect glycemic responses.

Prediction of glycemic index among high-sugar, low-starch foods.

A weighted mean of the glycemic index (GI) values of the constituent sugars of a non-starchy fruit is known to give a rough estimate of the GI of that fruit. Previously observed GI values (GIob) were, on average, lower than the calculated GI of the sugar mixture (GIsm) for nine acidic fruits (pH of 3.24-4.17) and tended to exceed the GIsm for six near-neutral non-starchy foods (pH < 5.33). A formula for predicting GI from GIsm and food pH was developed, and it accounted for 69% of the sum of squares for the 15 GIob values. A model that proposed that organic acids and their acidic anions slow gastric emptying and thereby lower GI was developed, and it was found to account for 57% of the GIob sum of squares. The substances responsible for lowering GI in acid fruits and the mechanisms of their action remain to be identified.

Breath hydrogen and methane responses of men and women to breads made with white flour or whole wheat flours of different particle sizes.

OBJECTIVE: While it is well known that consumption of whole grain foods results in beneficial health effects, the great majority of Americans prefer bread made with white flour. Consumption of whole grain foods in high fiber menus may cause undesirable intestinal responses. The purpose of this study was to determine whether consumption of bread made with ultra fine ground whole wheat flour retained beneficial effects while reducing undesirable effects. METHODS: Twenty-six men and women (31 to 55 years of age) consumed glucose solutions or bread made with white, whole wheat or fine ground whole wheat flour (1 g carbohydrate/kg body weight) in a Latin square design after two days of controlled diet. Breath methane and hydrogen were determined over the 24 hours after consumption of test foods. RESULTS: Hydrogen and methane responses of men and women were similar. There were no significant differences in methane responses to the different treatments, but hydrogen response was increased by all breads (p<0.0001). Although the overall mean response values were similar for all three breads, the patterns of hydrogen response differed (treatment*time, p<0.003). Gastrointestinal symptoms were not associated with fiber content or particle size of bread; however, subjects reporting symptoms tended to have higher methane responses (0.05

Breath hydrogen and methane expiration in men and women after oat extract consumption.

Oat extract has been shown to modify blood glucose response and fasting lipids after dietary incorporation although some abdominal discomfort and increased flatulence were noted. To determine the extent of gas production, hydrogen and methane were determined after tolerance tests containing cooked and uncooked oat extract and after dietary incorporation. Breath gases were determined before and periodically after tolerance tests. Study 1: While consuming a maintenance diet, 24 subjects (55.3-112.5 kg body weight) underwent a tolerance test (1 g carbohydrate/kg body wt) of glucose (GTT, 1700 kJ/100 g) or uncooked, baked, or boiled pudding [2191 kJ/100 g carbohydrate, (0.67 glucose and 0.33 oat extract containing 10 g/100 g beta-glucan)]. Hydrogen and methane expiration after all tolerance tests with the oat extract puddings, regardless of cooking method, was significantly higher than expirations after the GTT. Cooking the oat extract did not significantly change hydrogen or methane expiration. Study 2: Twenty-three subjects consumed a maintenance diet followed by the incorporation of oat extracts (50 g/8.33 MJ, 1 or 10 g/100 g beta-glucan) to the diet in a crossover pattern. A GTT and a tolerance test containing 0.67 g glucose and 0.33 g of the respective oat extract/kg body weight were consumed after the maintenance and oat extract diet periods. Breath hydrogen was significantly higher after both oat extract tolerance tests than after the GTT. Hydrogen excretion after the 10% beta-glucan oat extract was higher at 4, 5 and 6 h than after the 1% beta-glucan oat extract; breath methane was not significantly different. These data indicate that cooking did not alter the influence of oat extracts on intestinal function, and increased beta-glucan marginally increased hydrogen expiration.

Breath-hydrogen production and amylose content of the diet.

Recommendations to increase dietary intakes of starch and fiber in the United States may result in increased intake of resistant starch. High-amylose starch appears to resist digestion in vitro. To investigate the in vivo effect of high-amylose starch, diets containing 70% amylose or amylopectin cornstarches were fed for 14 wk each in a crossover design to 24 men [10 control, 14 hyperinsulinemic (HI)]. Fasting breath samples and periodic postingestion samples were analyzed for hydrogen during weeks 12 (nibbling tolerance test) and 14 (acute tolerance test) of each phase. Overall breath hydrogen was significantly higher after the amylose tolerance tests (nibbling, P < 0.0005; and acute, P < 0.0006). Control subjects, regardless of body mass index (BMI; in kg/m2), appeared to adapt to the high-amylose starch diet. Fasting breath hydrogen was significantly higher at week 12 but not at week 14 in HI subjects with a low BMI (< 25) consuming amylose than in other subjects. Breath hydrogen of the HI subjects with a moderate (between 25 and 27.8) or high (> 27.8) BMI increased from week 12 to week 14. The HI subjects with a high BMI averaged lower breath-hydrogen expiration than other HI subjects. After 3 d of excess energy intake, breath hydrogen after amylose was still significantly greater than after amylopectin (P < 0.019); fasting breath hydrogen of the control subjects after amylose more closely resembled that of the HI subjects. HI subjects with a high BMI may be more efficient at digesting all starch, therefore decreasing the amount available for colonic digestion. This may be a factor contributing to their greater body weight.

Dietary fiber: nutritional lessons for macronutrient substitutes.

The wide array of low-fat foods containing soluble fibers have the potential for helping in weight loss or weight control. Consumption of soluble fibers in sufficient quantities has been shown to lower serum lipid concentrations and to improve glycemic response. Some individuals could, eventually, consume a significant portion of their soluble dietary fiber from processed foods containing soluble-fiber fat substitutes. Changes in dietary fiber and starch sources increase the amount of fermentable material reaching the colon. Short-chain fatty acids thus produced are used as an energy source by colonocytes and may inhibit hepatic cholesterol synthesis. However, colonic fermentation can also result in flatulence or diarrhea. In addition, some diets high in soluble fiber have been shown to change intestinal cell morphology in rats. The possible benefits from consumption of a diet high in soluble fiber fat substitutes in serum lipid reduction, glycemic response improvement, and/or weight reduction as well as potential problems in flatulence, mineral absorption, and colonic cell hyperproliferation should be investigated.

Effect of beta-glucan level in oat fiber extracts on blood lipids in men and women.

OBJECTIVE: An active hypolipidemic component in oats, the soluble fiber beta-glucan, has been concentrated in an oat fiber extract. The oat fiber extract has been used to replace fat in food products. This study was designed to determine if moderate levels of oat fiber extract could be incorporated into a typical diet and whether plasma lipids could be reduced by the amount of beta-glucan added to the diet. METHODS: Oat fiber extracts containing low (1% by weight) or high (10% by weight) beta-glucan were fed to 23 mildly hypercholesterolemic subjects (seven men and 16 women). A maintenance diet was fed for 1 week followed by diet containing an oat extract for 5 weeks each in a crossover pattern. Five percent of the energy from fat in the maintenance diet was replaced with the oat extract in the experimental diets. Caloric intake was adjusted to try to maintain each subject's initial weight. Fasting blood was collected several days apart after separate 12 hour fasts the end of each period. Plasma was analyzed for triglycerides, total cholesterol, and lipoprotein cholesterol fractions. RESULTS: HDL, HDL2, and VLDL cholesterol, and triglyceride levels after the oat extract diets were not significantly different from those after the maintenance diet. Total and LDL cholesterol levels decreased significantly (p < 0.001) from maintenance levels after both diets containing the oat extracts. Total cholesterol levels after the higher beta-glucan extract diet were significantly lower than those after the low beta-glucan diet. CONCLUSIONS: Beneficial reduction of cholesterol was obtained with modest amounts of oat extract incorporated into the diet. A significant dose response due to beta-glucan concentration in the oat extract was observed in total cholesterol levels.

Dietary starch composition and level of energy intake alter nutrient oxidation in "carbohydrate-sensitive" men.

The effect of dietary starch type on components of 24-h energy expenditure (total, sleep, exercise) were examined in 13 hyperinsulinemic and nine control men, aged 28-58 y. Subjects consumed products containing 70% amylopectin or 70% amylose cornstarch for two 14-wk periods in a crossover design. A 10-wk period of starch replacement in the subjects' self-selected diets was followed by a 4-wk controlled feeding period at 100% maintenance energy intake; diets during the last 4 d of the controlled feeding period provided excess energy, i.e., 125% of maintenance energy. Data for insulin, glucose, 24-h energy expenditure and its components, respiratory quotient and nutrient oxidation were analyzed by ANOVA for mixed models. Although insulin and glucose responses to a starch tolerance test remained greater for hyperinsulinemic than for control subjects, both were reduced with high amylose consumption (P < 0.04). No component of energy expenditure was significantly affected by dietary starch or subject type. However, excess energy intake did increase metabolic energy expenditure (P < 0.0001). Protein oxidation increased with excess energy intake when subjects consumed the high amylopectin starch but did not increase in response to excess energy consumption when the high amylose diet was consumed, suggesting increased protein retention. The magnitude of the response in carbohydrate and fat oxidation was blunted in hyperinsulinemic subjects consuming excess levels of the amylose diet. This may be due to an improvement in overall insulin response or to a change in available substrates for oxidation resulting from microbial fermentation.

Resistant starch as energy.

OBJECTIVE: This study was designed to compare the metabolizable energy of two starch sources, standard cornstarch and high amylose cornstarch. METHODS: Diets containing 70% amylose (AM) or 70% amylopectin (AP) cornstarches were fed to 10 control and 14 hyperinsulinemic men for 14 weeks. During the last 4 weeks of each period, subjects were fed a controlled diet containing 34% of total energy from fat, 15% from protein and 51% from carbohydrate (55% of carbohydrate provided AM or AP). Duplicate food and all urine and feces were collected during the second week of the controlled diets for energy, nitrogen, fiber and starch determinations. Metabolizable energy (ME) was calculated as [energy intake minus (fecal plus urinary energy excretion)]. RESULTS: Total fiber uncorrected for resistant starch was 35.2 g and 48.8 g in the AP and AM diets, respectively. The AM diet contained an average of 29.7 g resistant starch (16% of total starch) while the AP diet averaged 0.8 g (less than 0.01%). ME was not significantly different between the AM and AP diets nor between the control and hyperinsulinemic subjects. Fecal energy and nitrogen was significantly higher after the AM compared to AP diet. Based on energy intake and fecal excretion from all subjects, the partial digestible energy value for the resistant starch averaged 11.7 kJ/g resistant starch which was 67.3% of the energy of standard cornstarch. Control and hyperinsulinemic subjects differed in their ability to digest resistant starch, averaging 81.8% and 53.2, respectively. The hyperinsulinemic, but not control, subjects had significantly higher breath hydrogen expirations (LS means, p > 0.05) in the fasting, 1-5 hours and 7 hour collections after consuming the AM when compared to the AP tolerance meal. CONCLUSIONS: The type of starch consumed in the diet did not statistically affect metabolizable energy. Based on ME and breath hydrogen expiration, amylose and the resistant starch from amylose appears to be utilized as an energy source. Resistant starch averaged 2.8 kcal/g for all 24 subjects but only 2.2 kcal/g in the hyperinsulinemic subjects.

Contribution of fiber and resistant starch to metabolizable energy.

Recommendations made to increase complex carbohydrate and fiber intake in the United States may result in energy loss from increased fecal losses of starch, protein, and fat. The type of fiber or starch and the amount consumed affect digestion of the carbohydrate and interactions with other nutrients. On average, 8.4 kJ (2 kcal) digestible energy/g is available from up to 70 g poorly digested carbohydrate/d. Undigested fiber and starch are important substrates for colon bacteria and are fermented to short-chain fatty acids, hydrogen, and methane. Hydrogen and methane excreted through the lungs have been used as indicators of colonic fermentation. Fermentation appears to contribute significant digestible energy when > 20 g poorly digested carbohydrate/d is consumed.

Effect of long-term consumption of amylose vs amylopectin starch on metabolic variables in human subjects.

Long-term consumption of high-amylose starch on insulin and glucose response was investigated in 24 men: 10 control and 14 hyperinsulinemic (HI) subjects. Subjects consumed products made with standard (70% amylopectin, 30% amylose) or high-amylose (70% amylose, 30% amylopectin) cornstarch for two 14-wk periods in a crossover pattern. Starch products replaced usual starches in the self-selected diet for 10 wk followed by 4 wk of a controlled diet. After a starch-tolerance test with bread made from the starch consumed during that period, the insulin response curve area was significantly lower in all subjects after amylose consumption (P < 0.002). Glucose responses in HI and control subjects were similar and did not vary with the type of starch. Fasting triglyceride concentrations were significantly lower in subjects who consumed the high-amylose compared with the standard-starch diet throughout the study. Chronic consumption of high-amylose foods normalized the insulin response of hyperinsulinemic subjects and showed a potential benefit for diabetic subjects.

Diets containing soluble oat extracts improve glucose and insulin responses of moderately hypercholesterolemic men and women.

The high amount of soluble beta-glucans in oats may be responsible for beneficial effects on glucose tolerance and blood lipids. We studied 16 women and 7 men (aged 38-61y) with moderately high cholesterol concentrations who consumed normal diets to which oat extracts with either 1% or 10% soluble beta-glucans were added. Oat extracts comprised 10% of energy and were consumed in a 5-wk crossover design after a 1-wk equilibration period. At the end of the equilibration period and each 5-wk period, a carbohydrate tolerance test was conducted and responses to glucose, glucose plus oat extract containing 1% glucan, or glucose plus oat extract containing 10% glucan were determined. Glucose responses were reduced by both extracts in both men and women; however, in women, responses to the 10% extract were lowest. Insulin responses did not differ between men and women, but were lower after oat extracts. Glucagon responses were higher initially in men and were lowered after oat extracts in men but not in women. Modest amounts of oat extracts can be incorporated into normal diets with beneficial effects on glucose tolerance factors.

Prediction of glycemic index for starchy foods.

Associations between published values for glycemic index (GI) and chemical components were examined by regression analysis in 18 starchy foods. Independent variables were the amounts of protein, fat, phytic acid, and total dietary fiber (TDF) present in food portions containing 50 g available carbohydrate. GI was similarly and significantly correlated (P < 0.05) with TDF, protein, and phytate. When foods were considered as comprising two groups, legumes and others (grains and tubers), food category accounted for as large a fraction of variability in GI as did regression analysis with food components in the undivided sample. Most correlations between GI and components reverted toward zero when calculated only for the legumes or the "others" group. Evidence is cited that the method of preparing foods and the characteristics of starch and starch granules are more important in predicting GI among starchy food than is the content of any of these four food components.

Effect of soluble fibers on plasma lipids, glucose tolerance and mineral balance.

Fibers are broadly classified as soluble and insoluble based on their physical or analytical properties. Two human studies have been carried out in this laboratory utilizing soluble gums. The first compared a low fiber diet to the diet with an average of 19.5 g of added fiber per day from cellulose, an insoluble fiber, or carboxymethylcellulose gum, karaya gum or locust bean gum, all soluble fibers. Plasma cholesterol levels but not triglycerides were significantly lower when the soluble gums were consumed for 4 weeks each. Glucose and insulin response curves after a standard glucose tolerance test were not significantly different between the 5 diets. Adding refined fibers to the basal diet did not significantly affect apparent mineral balance of calcium, magnesium, manganese, iron, copper or zinc, with the exception of a negative manganese balance after carboxymethylcellulose. The second study added an average of 31.7 g of guar gum per day to the diets of non-insulin dependent diabetic individuals for 6 months. Lipid levels observed at the beginning of the study were not reduced in either group, placebo or guar gum supplemented. Consumption of guar gum significantly reduced the C-peptide but not the glucose response curve. The number of insulin receptors increased while affinity remained the same. Apparent mineral balance was not affected by the consumption of guar gum for 6 months. The combined results of these studies indicates that soluble refined gums may have therapeutic value in reducing cholesterol and improving glucose metabolism without adversely affecting most mineral balances.

Effect of guar gum on mineral balances in NIDDM adults.

The self-selected diet of 16 subjects with non-insulin-dependent diabetes mellitus (NIDDM) was supplemented for 6 mo with either a granolalike bar containing 35.5 g carbohydrate and 6.6 g guar gum/bar or a placebo bar containing carbohydrate but no guar gum. Subjects consumed a mean of 4.8 bars/day. Average guar gum consumption at the end of the study was 31.7 g/day. One week before and at the end of the study, subjects were admitted to a metabolic ward and fed a controlled diet similar to their self-selected diet. Food, feces, and urine were composited for analysis of iron, zinc, copper, calcium, magnesium, and manganese. Eight subjects consuming the guar gum supplement and 6 subjects consuming the placebo bar completed collections for mineral balance. Neither consumption of guar gum nor placebo bar significantly changed apparent mineral balance for iron, copper, zinc, calcium, manganese, or magnesium from prestudy levels to 6-mo levels, and no significant differences were observed between the two groups. With the exception of copper, men consumed significantly more minerals than women. We conclude that consumption of guar gum by patients with NIDDM does not adversely affect apparent mineral balance.

Diets containing high amylose vs amylopectin starch: effects on metabolic variables in human subjects.

Twelve men consumed a diet containing 34% of calories as 70% amylose or amylopectin starch to determine if the structure of starch could influence metabolic factors associated with abnormal states. Each starch was fed to subjects for 5 wk in a crossover design. No significant differences were observed in glucose or insulin levels when a glucose tolerance was given after 4 wk on each starch. However, glucose and insulin responses were significantly lower when a meal containing amylose compared with amylopectin was consumed after 5 wk on each starch. Summation of 0.5 through 2-h levels of insulin but not glucose were significantly lower after amylose compared with levels after amylopectin. Mean fasting triglyceride and cholesterol levels were significantly lower during the period when amylose was consumed. Long-term intake of dietary amylose may be valuable in decreasing insulin response while maintaining proper control of glucose tolerance and low levels of blood lipids.

Effect of starch structure on glucose and insulin responses in adults.

Twelve women and 13 men were given meals containing cornstarch with 70% of the starch in the form of amylopectin or amylose to determine if differences in glycemic response result from different chemical structure. Blood was drawn before and 30, 60, 120, and 180 min after each meal. The meals consisted of starch crackers fed at the rate of 1 g carbohydrate from starch per kilogram body weight. The amylose meal resulted in a significantly lower glucose peak at 30 min than did the amylopectin meal. Plasma insulin response was significantly lower 30 and 60 min after amylose than after the amylopectin meal. Summed insulin above fasting was significantly lower after amylose while summed glucose was not significantly different between the two meals. The sustained plasma glucose levels after the amylose meal with reduced insulin requirement suggest amylose starch may be of potential benefit to carbohydrate-sensitive or diabetic individuals.

A study on Asian Indian and American vegetarians: indications of a racial predisposition to glucose intolerance.

Sixty-two Asian Indian and American vegetarians participated in a 3-h glucose tolerance test after an overnight fast to study clinical indices of glucose homeostasis. The Asian Indians had a higher (p less than 0.0035) insulinogenic score than the Americans. The Asian Indians had significantly higher insulin levels than the Americans at every sampling time during the glucose tolerance test except for the 3-h sample. The Indian men had significantly higher (p less than 0.05) plasma glucose than the other three groups at 2 h after the glucose load. American subjects had higher (p less than 0.0008) insulin binding to erythrocytes than the Asian Indian subjects. Scatchard analysis and competition-inhibition plots of the insulin-receptor data indicated that decreased binding in the Indian group results from a lowered number and decreased affinity of erythrocyte receptors. These results suggest that Asian Indians exhibit several clinical indications associated with an increased risk for the development of insulin-independent diabetes.