Kay M. Behall

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.

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 subjects 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.

Lipids Significantly Reduced by Diets Containing Barley in Moderately Hypercholesterolemic Men

Objective: To determine whether barley, as the soluble fiber source, would beneficially change cardiovascular risk factors. Soluble fiber from oats has been recognized as beneficial in decreasing blood cholesterol levels. Although barley contains high amounts of soluble fiber, it is not consumed as extensively as oats. Methods: Eighteen moderately hypercholesterolemic men (28–62 y) consumed a controlled equilibration diet (Step 1, 30% fat, 55% carbohydrate, 15% protein, < 300 mg cholesterol) for 2 weeks followed by the diet with about 20% of energy replaced with brown rice/whole wheat, ½ barley & ½ brown rice/whole wheat or barley (< 0.4 g, 3 g and 6 g added soluble fiber/2800 kcal, respectively) for 5 weeks in a Latin square design. Fasting blood was drawn twice weekly. Total cholesterol, HDL cholesterol, and triacylglycerols were measured enzymatically and lipid fractions were measured by nuclear magnetic resonance spectroscopy. Results: Compared with prestudy concentrations, total cholesterol (14%, 17%, and 20%, respectively) and LDL cholesterol (17%, 17%, and 24%, respectively) were significantly lower (p < 0.0001) after the low, medium, and high-soluble fiber diets. Triacylglycerol was 6%, 10%, and 16% lower (p = 0.09) whereas HDL cholesterol (9%, 7%, and 18%) was higher (p < 0.001) after the experimental diets. Total cholesterol and LDL cholesterol after the high-soluble fiber diet were significantly lower than concentrations after the low- or medium-soluble fiber diets. Mean LDL particle number significantly decreased (p < 0.007) and the large LDL cholesterol fraction showed a trend toward lower concentrations (p = 0.06). Conclusion: Increasing soluble fiber through consumption of barley in a healthy diet can reduce cardiovascular risk factors.

GLUCOSE AND INSULIN RESPONSES TO WHOLE GRAIN BREAKFASTS VARYING IN SOLUBLE FIBER, BETA-GLUCAN: A DOSE RESPONSE STUDY IN OBESE WOMEN WITH INCREASED RISK FOR INSULIN RESISTANCE

BACKGROUND A high intake of whole grains containing soluble fiber has been shown to lower glucose and insulin responses in overweight humans and humans with type 2 diabetes. AIM OF THE STUDY We investigated the linearity of this response after consumption of 5 breakfast cereal test meals containing wheat and/or barley to provide varying amounts of soluble fiber, beta-glucan (0, 2.5, 5, 7.5 and 10 g). METHODS Seventeen normoglycemic, obese women at increased risk for insulin resistance consumed 5 test meals within a randomized cross-over design after consuming controlled diets for 2 days. Blood samples for glucose and insulin response were obtained prior to and 30, 60, 120 and 180 min after consuming the test meals. RESULTS Consumption of 10 g of beta-glucan significantly reduced peak glucose response at 30 min and delayed the rate of glucose response. Area under the curve for 2 h-postprandial glycemic response was not affected by beta-glucan content. However, peak and area under the curve of insulin responses were significantly affected by the beta-glucan amount in an inverse linear relationship. CONCLUSION These data suggest that acute consumption of 10 g of beta-glucan is able to induce physiologically beneficial effects on postprandial insulin responses in obese women at risk for insulin resistance.

Comparison of Hormone and Glucose Responses of Overweight Women to Barley and Oats

Objective: To determine the effect of particle size (flour vs. flakes) on glycemic responses after oats and barley (Prowashonupana cultivar), which contain high amounts of soluble fiber, are consumed by overweight women. Design: Ten women, average age 50 years and body mass index 30, consumed glucose (1 g/kg body weight) and four test meals (1 g carbohydrate/kg body weight; 2/3 of the carbohydrate from oat flour, oatmeal, barley flour, or barley flakes and 1/3 from pudding) in a Latin square design after consuming controlled diets for 2 days. Blood samples were collected at fasting and periodically after each meal. Results: Peak glucose and insulin levels after barley were significantly lower than those after glucose or oats. Glucose areas under the curve (AUCs) after test meals compared with AUCs after glucose were reduced after both oats and barley (29–36% by oats and 59–65% by barley) (p < 0.002). Insulin AUCs after test meals compared with glucose AUCs were significantly reduced only by barley (44–56%) (p < 0.005). Indexes for insulin resistance (HOMA, MFFM, Cederholm) after the oat and barley meals were not different from indexes after the glucose meal. Glucagon and leptin responses did not significantly differ for the carbohydrates tested. Conclusions: Particle size of the oats or barley had little effect on the glycemic responses. Both oat and barley meals reduced glycemic responses; the high soluble fiber content of this barley appeared to be a factor in the greater reduction observed.

Seasonal variation in plasma glucose and hormone levels in adult men and women.

Twenty-nine men and women collected diet records for 1 yr. Fasting blood samples were collected four times during the year so that each season of the year was represented. An oral glucose tolerance test was given in the spring and in the fall. Regardless of season men consumed significantly more kilocalories, carbohydrate, sugar, and starch than did the women. Men consumed more simple sugars in the fall than in the spring. No seasonal effect was observed for calories, total carbohydrate, or starch intake. Fasting glucose and insulin were higher in the fall than in the spring. Summed insulin levels after the oral glucose tolerance were significantly different by age and season. Summed insulin levels were significantly higher in older than younger subjects; men and older subjects had higher levels in the spring than in the fall. Fasting levels of thyroxine, free thyroxine, triiodothyronine, and glucagon varied significantly with the season. A significant sex by season interaction was observed in the thyroid hormones. It appears that seasonal variation as well as diurnal variation should be considered in evaluating hormone levels.

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.

Short-Term Satiety and Glycemic Response After Consumption of Whole Grains with Various Amounts of beta-Glucan

The effects of a meal with and without soluble dietary fiber in the form of beta-glucan on short-term satiety and glucose response were investigated in 19 overweight subjects. Subjects consumed four isocaloric test meals consisting of a glucose solution or wheat (0 g of beta-glucan), a wheat-barley mixture (1 of beta-glucan), or barley (2 of P-glucan) served as cooked cereal with low-fat strawberry yogurt. Subjects used visual analog scales (VAS) to rate their hunger, fullness, satisfaction, thirst, nausea, and drowsiness at timed intervals before and after consumption of each test meal. Blood glucose was measured periodically, and energy intake was recorded 2 hr after consumption of each test meal. In women peak glucose responses and area under the curve were significantly lower after consumption of 2 of beta-glucan compared with consumption of 0 or 1 g of beta-glucan. VAS ratings did not significantly differ among cereals. In men no effect of glucan on glucose response was observed, and beta-glucan had only a marginal effect oil VAS ratings. Energy intake was not affected by beta-glucan level in either women or men. The findings indicate that acute reduction of glycemic response in overweight women requires the comsumption of at least 2 g of beta-glucan per meal, and greater amounts of beta-glucan per meal may be required to achieve substantial satiety effects in overweight women and men.

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.

Food Amylose Content Affects Postprandial Glucose and Insulin Responses

ABSTRACT Beneficial reduction in glycemic response has been observed after consumption of some high-amylose foods. This study examined the effect of varying the moisture content and the particle size of the starch in a test food. Twelve men and 12 women consumed corn chips or corn muffins made with starch or starch plus cornmeal from standard corn (30% amylose, 70% amylopectin) or high amylose (70%) corn. Half of the subjects were hyperinsulinemic based on a prestudy glucose challenge. No gender differences were observed. The hyperinsulinemic subjects had significantly higher insulin and glucose responses and area under the curve as compared with the normal responders. Average glucose, insulin and glucagon were usually lower after muffins compared with chips or foods containing cornmeal. Insulin and glucose responses, but not glucagon, were significantly lower after the consumption of foods made with high-amylose compared with standard corn starch and in control versus hyperinsulinemic subjects. Average p...