Barbara O. Schneeman

Fiber, Inulin and Oligofructose: Similarities and Differences

The biological, chemical and physical properties of dietary fibers are associated with physiologic actions in the small and large intestine that have important metabolic implications for health. These properties of fiber include dispersibility in water, bulk, viscosity, adsorption and binding of compounds and fermentability. Dietary fructans share some of the properties of dietary fiber and thus are likely to have similar metabolic effects. Within the small intestine, properties such as dispersibility in water, bulking and viscosity are associated with slowing the digestion and absorption of carbohydrate and lipid and promoting nutrient absorption along a greater length of the small intestine. Both of these actions are related to cholesterol reduction and blunting of alimentary gylcemia. Although fructans are dispersible in water and will provide some bulk because they are nondigestible in the small intestine, they do not appear to be associated with significant increases in viscosity. Thus one would predict that any immediate effects on alimentary glycemia or on cholesterol reduction are likely to be modest compared with more viscous polysaccharides. Fermentability and bulking capacity of nondigestible carbohydrates define an essential role of fiber in maintaining gastrointestinal health. Within the large intestine, carbohydrates that are not digested in the small intestine are available for fermentation by the microflora present. Carbohydrates that are dispersible in the aqueous phase are more readily digested by microbes. A large body of evidence indicates that dietary fructans are digested in the large intestine, resulting in an increase in microbial mass and production of short-chain fatty acids.

Effect of Barley β-Glucan in Durum Wheat Pasta on Human Glycemic Response

ABSTRACT High-fiber, high-carbohydrate diets, including foods with low glycemic index, have been associated with prevention and treatment of diseases such as coronary heart disease and diabetes. β-glucan, a soluble, viscous polymer found in oat and barley endosperm cell wall, was incorporated into pasta test meals. Five fasted adult subjects were fed test meals of a barley and durum wheat blend pasta containing 100 g of available carbohydrate, 30 g of total dietary fiber (TDF) and 12 g of β-glucan, or an all durum wheat pasta containing the same amount of available carbohydrate, 5 g of TDF, and negligible β-glucan. The β-glucan and durum wheat pasta resulted in a lower glycemic response as measured by average total area and maximum increment of the blood glucose curves. Lower insulin response to the β-glucan and durum wheat pasta was also indicated by lower average area and increment characteristics of the insulin curves. Barley β-glucans may be an economical and palatable ingredient for processed food pr...

Gastrointestinal physiology and functions

While the health benefit of a functional food may be a metabolic response that lowers risk for disease, the actual target for the food or food component may be on the functioning of the gastrointestinal tract (GIT). For example, slowing absorption from the intestine, as measured by examining the appearance of the nutrient or food component in the blood, the hormone response associated with absorption of the compound or excretion of the compound, may provide a health benefit. However, the food component may slow absorption by delaying gastric emptying, altering the mixing within the intestinal contents or decreasing the availability of digestive enzymes in the intestine. These measures of GIT function provide validation of the mechanisms by which the functional food or food components affect metabolism. Bioavailability of physiologically active compounds from foods will be determined by the digestibility of foods that contain these compounds, their subsequent absorption and utilization by tissues. The physical structure of foods contributes to the functional effects of foods as well as to the availability of compounds from foods. For example, recent studies have demonstrated that changing the viscosity of the gut contents alters absorption and GIT response. Additionally, food structures such as the plant cell wall change the availability of absorbable compounds along the gastrointestinal contents. The areas of probiotics and prebiotics have highlighted the potential importance of gut microflora in health. While evidence suggests biological activity relevant to disease risk reduction, the long-term implications of the microbial activity have yet to be established.

Effect of n−3 fatty acid-rich fish oil supplementation on the oxidation of low density lipoproteins

This study was aimed at determining the effect of fish oil supplementation on copper-catalyzed oxidation of low density lipoproteins (LDL) from nine hypertriglyceridemic human subjects. A rapid headspace gas chromatographic method was used to measure the volatile oxidation products from LDL. Propanal and hexanal were the major volatile products formed in the oxidation of n−3 and n−6 polyunsaturated fatty acids (PUFA), respectively. Fish oil supplementation resulted in a significant increase in propanal formation from 3.7 to 13.4 nmol/mL LDL (P<0.01); it also resulted in small decreases in pentanal formation from 14.7 to 11.4 nmol/mL LDL and in hexanal formation from 138 to 108 nmol/mL LDL (P<0.05). The changes in peroxidation products paralleled the changes in LDL composition, which showed a significant increase in n−3 PUFA from 3.2 to 14.6% (P<0.01) and a decrease in n−6 PUFA from 43.7 to 35.0% (P<0.05). Propanal formation was highly and significantly correlated with n−3 PUFA content (r=0.950,P<0.001). Since total volatiles remained unchanged, this indicated that the two groups of LDL samples did not differ in overall oxidative susceptibility. Although fish oil intake did not alter the oxidative susceptibility of LDL, the chemically modified LDL particles generated a distinct pattern of volatile oxidation products that reflected changes in their fatty acid composition.

Effects of a carotene-deficient diet on measures of oxidative susceptibility and superoxide dismutase activity in adult women

The effect of consuming a low carotene diet (approximately 60 micrograms carotene/day) on oxidative susceptibility and superoxide dismutase (SOD) activity in women living in a metabolic research unit was evaluated. The diet had sufficient vitamins A, E, and C. The women ate the diet supplemented with 1500 micrograms/day beta-carotene for 4 days (baseline), then the unsupplemented diet for 68 days (depletion), followed by the diet supplemented with > 15,000 micrograms/day carotene for 28 days (repletion). Production of hexanal, pentanal, and pentane by copper-oxidized plasma low density lipoproteins from carotene-depleted women was greater than their production of these compounds when repleted with carotene. Erythrocyte SOD activity was depressed in carotene-depleted women; it recovered with repletion. Thiobarbituric acid reactive substances in plasma of carotene-depleted women were elevated and diminished with repletion. Dietary carotene seems to be needed, not only as a precursor of vitamin A, but also to inhibit oxidative damage and decrease oxidation susceptibility.

Effects of dietary fiber on digestive enzyme activity and bile acids in the small intestine.

In humans and in a number of animal species consumption of high fiber diets has been associated with reductions in the digestibility and availability of protein, fats, and other nutrients such as minerals, vitamins, and carbohydrates. The ability of fiber to alter the rate of digestion and absorption in the gastrointestinal tract appears to be important in understanding its effects on metabolism, such as reducing plasma lipids and altering the glycemic response to a meal. The assimilation of nutrients from the diet requires the movement of digesta through the gastrointestinal tract, the enzymatic hydrolysis of complex compounds into simpler compounds which can be absorbed, the uptake of these compounds into the intestinal cell, and movement of nutrients from the intestinal cells to the portal circulation or lymph ducts. Dietary fibers influence these processes through several mechanisms which include altering the availability of bile acids and digestive enzyme activity, changing the characteristics of the intestinal contents where digestion occurs, altering the morphology of the small intestine so that structural changes are associated with functional changes in the gut, and causing adaptation in the synthesis of enzymes or compounds needed for nutrient absorption from the intestine. The objective of this paper is to consider the potential effects of dietary fiber on the rate of digestion in the small intestine. The effects of fiber on absorption from the intestine and subsequent metabolism of nutrients will be considered in other papers in this series. One of the first questions to consider is the effect of various sources of dietary fiber on the activity of digestive enzymes in vitro. Several studies have reported changes in the activity of pancreatic enzymes following incubation with purified and nonpurified fiber sources (1-9).

Cholecystokinin and serotonin receptors in the regulation of fat-induced satiety in rats

The present study investigated the relationship between endogenous CCK and serotonin (5-HT) in fat-induced satiety. Male Wistar rats with duodenal cannulas were adapted to eating 6 h/day along with receiving an infusion of saline or one of two isocaloric solutions (10 ml, 1 kcal/ml, 0.45 ml/min) varying in fat and carbohydrate content (20 or 80% energy from fat). Rats were infused 10 min after food presentation. The satiation/satiety response was determined from measures of meal size (MS), intermeal interval (IMI), and total food intake (TFI). Infusion with either fat solution reduced MS compared with saline; however, the 80% fat infusate reduced TFI and lengthened the IMI compared with saline and the 20% fat infusate. CCK and 5-HT involvement in fat-induced satiety was investigated by preceding the 80% fat infusate with CCK and/or 5-HT3 receptor antagonists Devazepide (Dev) and Tropisetron (Trop). A CCK releaser, trypsin inhibitor (TI), was added to the 20% fat infusate to enhance satiety. Pretreatment with Dev or Trop alone attenuated the inhibitory effects of the 80% solution on IMI, whereas reversal of the inhibitory effects on MS and TFI were sensitive only to Dev at the doses provided. Both antagonists together completely blocked the satiating effects of the 80% fat infusate on all feeding variables measured. Addition of TI to the 20% fat infusate lengthened the IMI but did not affect MS or TFI. These results provide evidence for the participation of both endogenous CCK and 5-HT in the satiety response to fat in the intestine.The present study investigated the relationship between endogenous CCK and serotonin (5-HT) in fat-induced satiety. Male Wistar rats with duodenal cannulas were adapted to eating 6 h/day along with receiving an infusion of saline or one of two isocaloric solutions (10 ml, 1 kcal/ml, 0.45 ml/min) varying in fat and carbohydrate content (20 or 80% energy from fat). Rats were infused 10 min after food presentation. The satiation/satiety response was determined from measures of meal size (MS), intermeal interval (IMI), and total food intake (TFI). Infusion with either fat solution reduced MS compared with saline; however, the 80% fat infusate reduced TFI and lengthened the IMI compared with saline and the 20% fat infusate. CCK and 5-HT involvement in fat-induced satiety was investigated by preceding the 80% fat infusate with CCK and/or 5-HT3 receptor antagonists Devazepide (Dev) and Tropisetron (Trop). A CCK releaser, trypsin inhibitor (TI), was added to the 20% fat infusate to enhance satiety. Pretreatment with Dev or Trop alone attenuated the inhibitory effects of the 80% solution on IMI, whereas reversal of the inhibitory effects on MS and TFI were sensitive only to Dev at the doses provided. Both antagonists together completely blocked the satiating effects of the 80% fat infusate on all feeding variables measured. Addition of TI to the 20% fat infusate lengthened the IMI but did not affect MS or TFI. These results provide evidence for the participation of both endogenous CCK and 5-HT in the satiety response to fat in the intestine.

Meal pattern analysis to investigate the satiating potential of fat, carbohydrate, and protein in rats

We examined meal patterns after isocaloric duodenal infusions of fat, carbohydrate (CHO), and protein by measuring meal size, intermeal interval (IMI) and total food intake (TFI). Wistar rats were adapted to normal feeding 6 h/day, with continuous computer monitoring of feeding patterns. One of five solutions (10 ml of 1 kcal/ml at 0.45 ml/min; 0, 20, 50, 80, or 100% of energy from fat) or saline (control) was infused 10 min after initiation of eating. Separate rats received casein or casein hydrolysate at 18.5 or 37% energy. Equivalent energy loads varying in fat, CHO, and protein content compared with saline resulted in similar reductions in first meal intakes. The second meal did not differ among fat and CHO treatments including saline; however, infusion with a protein-containing solution increased the size of meal 2. The IMI was doubled by protein infusion independently of dose or source but extended dose dependently by fat. TFI was lower after high fat and higher after protein than after saline infusion. The results indicate that the concentrations of fat, CHO, and protein differentially affect the qualitative and quantitative aspects of feeding in rats.We examined meal patterns after isocaloric duodenal infusions of fat, carbohydrate (CHO), and protein by measuring meal size, intermeal interval (IMI) and total food intake (TFI). Wistar rats were adapted to normal feeding 6 h/day, with continuous computer monitoring of feeding patterns. One of five solutions (10 ml of 1 kcal/ml at 0.45 ml/min; 0, 20, 50, 80, or 100% of energy from fat) or saline (control) was infused 10 min after initiation of eating. Separate rats received casein or casein hydrolysate at 18.5 or 37% energy. Equivalent energy loads varying in fat, CHO, and protein content compared with saline resulted in similar reductions in first meal intakes. The second meal did not differ among fat and CHO treatments including saline; however, infusion with a protein-containing solution increased the size of meal 2. The IMI was doubled by protein infusion independently of dose or source but extended dose dependently by fat. TFI was lower after high fat and higher after protein than after saline infusion. The results indicate that the concentrations of fat, CHO, and protein differentially affect the qualitative and quantitative aspects of feeding in rats.

Use of the Food Guide Pyramid and US Dietary Guidelines to Improve Dietary Intake and Reduce Cardiovascular Risk in Active-Duty Air Force Members

OBJECTIVE To determine whether adoption of dietary patterns consistent with the US Dietary Guidelines for Americans and the Food Guide Pyramid, combined with exercise training, result in significant reductions in cardiovascular risk compared with a regimen of exercise therapy alone. DESIGN A randomized trial to compare the effects of exercise alone (n = 17) with the effects of exercise and dietary intervention (n = 15). SETTING McClellan Air Force Base medical clinic (Sacramento, Calif). SUBJECTS Thirty-two members of the Air Force (20 men and 12 women) were recruited at the time they entered a 90-day fitness improvement program. Mean age was 32 years. INTERVENTION All subjects participated in a 90-day fitness program. Half of the group received individualized dietary counseling using the Food Guide Pyramid as a primary educational tool. MAIN OUTCOME MEASURES Changes in body mass index, plasma lipids and lipoprotein levels, aerobic capacity, and dietary intake were selected to evaluate the effectiveness of the intervention. STATISTICAL ANALYSES PERFORMED Outcome measures were evaluated by analysis of variance. A paired t test was performed to compare changes in food-group servings and food-group fat intake from baseline values for the exercise-plus-diet group. RESULTS Percentage of energy from fat decreased from 39% to 23% for the exercise-plus-diet group, and servings from each of the food groups changed to reflect current guidelines. This group also had significant reductions in body mass index, total cholesterol level, and low-density lipoprotein level: 2% (P = .0001), 9% (P = .003), and 13% (P = .005), respectively. No change was observed for the exercise-only group. Additionally, a significant improvement in maximum oxygen consumption (P = .01) of 38% (vs 14% for the control group) was achieved. CONCLUSIONS Dietary modification in accordance with the Food Guide Pyramid and the US Dietary Guidelines results in significant reductions in known cardiovascular risk factors and improves the response to exercise training.

Mushrooms and Health Summit Proceedings

The Mushroom Council convened the Mushrooms and Health Summit in Washington, DC, on 9-10 September 2013. The proceedings are synthesized in this article. Although mushrooms have long been regarded as health-promoting foods, research specific to their role in a healthful diet and in health promotion has advanced in the past decade. The earliest mushroom cultivation was documented in China, which remains among the top global mushroom producers, along with the United States, Italy, The Netherlands, and Poland. Although considered a vegetable in dietary advice, mushrooms are fungi, set apart by vitamin B-12 in very low quantity but in the same form found in meat, ergosterol converted with UV light to vitamin D2, and conjugated linoleic acid. Mushrooms are a rare source of ergothioneine as well as selenium, fiber, and several other vitamins and minerals. Some preclinical and clinical studies suggest impacts of mushrooms on cognition, weight management, oral health, and cancer risk. Preliminary evidence suggests that mushrooms may support healthy immune and inflammatory responses through interaction with the gut microbiota, enhancing development of adaptive immunity, and improved immune cell functionality. In addition to imparting direct nutritional and health benefits, analysis of U.S. food intake survey data reveals that mushrooms are associated with higher dietary quality. Also, early sensory research suggests that mushrooms blended with meats and lower sodium dishes are well liked and may help to reduce intakes of red meat and salt without compromising taste. As research progresses on the specific health effects of mushrooms, there is a need for effective communication efforts to leverage mushrooms to improve overall dietary quality.