Position of The American Dietetic Association: health implications of dietary fiber

Dietary intake of total vegetable, fruit, cereal, soluble and insoluble fiber and risk of all-cause, cardiovascular, and cancer mortality: systematic review and dose-response meta-analysis of prospective cohort studies

Objectives

To conduct a systematic review and meta-analysis of prospective cohort studies to investigate the association between total, vegetable, fruit, cereal, soluble and insoluble fiber intake and risk of all causes, cardiovascular disease (CVD), and cancer mortality and quantitatively assess the dose-response relation.

Methods

Eligible studies were identified by searching PubMed, Embase and Web of science before August 2023. Random effects models were used to calculate summary relative risk (RR) and 95% confidence intervals (CI) and restricted cubic splines to model the linear/non-linear association.

Results

The summary RR for all-cause, CVD and cancer mortality of dietary fiber was 0.90 (95% CI: 0.86,0.93), 0.87 (0.84,0.91), 0.91 (0.88,0.93), respectively. Significant association was observed for all-cause and CVD mortality with fruit, vegetable cereal and soluble fiber intake and cancer mortality with cereal fiber intake. No significant association was found for insoluble fiber, vegetable or fruit fiber intake and cancer mortality. Dose-response analysis showed a significant non-linear relation of dietary fiber intake with all-cause mortality, and linear relation for others.

Conclusions

Higher dietary fiber including different type and food sources of fiber intake were associated with lower risk of mortality. Our findings provide more comprehensive evidence on dietary fiber intake with mortality.

Systematic review registration

https://www.crd.york.ac.uk/prospero, identifier: CRD42022338837.

Effects of prebiotics in combination with probiotics on intestinal hydrolase activity, microbial population and immunological biomarkers in SD rats fed an AIN-93G diet

BACKGROUND

Gastrointestinal microbiota, which comprises hundreds of different types of microbes, biologically plays crucial roles in the host's health. Probiotics (PRO) did not always have a positive benefit on the host, depending on strains of microbes and the physiochemical properties of prebiotics (PRE), indicating that the properties of PRE in combination with PRO might have different effects on the gut ecology. The aim of this study was to assess the effects of insoluble or soluble PRE with PRO on intestinal digestive hydrolase, the fecal microbes, and immunological biomarkers in SD rats fed an AIN-93G diet.

RESULTS

Forty, 8-week-old SD rats were randomly assigned to 4 groups with 10 replicates in each; cellulose (CELL), cellulose + probiotics (CELPRO), oatmeal (OATS), and oatmeal + probiotics (OATPRO) groups. After 4-week feeding trial, rats were treated with saline or lipopolysaccharide (LPS, 1 mg/kg) to examine the alleviating effects of PRO and PRE on immunological responses. There was a significant (p < 0.05) decrease in feed intake of rats fed the oatmeal supplemented diet without affecting growth performance. Blood triglyceride was significantly (p < 0.05) decreased in rats fed the oatmeal diet, and aspartate aminotransferase (AST) was significantly (p < 0.05) decreased in rats fed the PRO supplemented diet. Intestinal maltase, sucrose, and lactase activities were significantly (p < 0.05) higher in rats fed PRO compared with rats not fed PRO. Rats fed the oatmeal showed a significant (p < 0.01) increase in the fecal colony forming units (CFU) of Lactobacillus plantarum, Bacillus subtilis, and Saccharomyces cerevisiae compared with those fed cellulose. LPS-treated rats fed PRO showed a significant (p < 0.05) increase in blood secretory immunoglobulin A (sIgA) compared with those not fed PRO. The LPS-treated rats fed PRO resulted in decreased (p < 0.05) blood IL-6 compared with those not fed PRO, indicating that a dietary PRO alleviated inflammatory response in LPS-treated rats.

CONCLUSIONS

Dietary oatmeal increased fecal microbes, and PRO supplement resulted in increased intestinal hydrolase and immune functions of the host, demonstrating that soluble PRE with supplemented with PRO could be a more bioactive combination of synbiotics in SD rats.

Soluble Fiber and Insoluble Fiber Regulate Colonic Microbiota and Barrier Function in a Piglet Model

The main purpose of the present study was to assess the effect of soluble and insoluble fiber on colonic bacteria and intestinal barrier function in a piglet model. A total of 24 piglets (25 ± 1 d old; 7.50 ± 0.31 kg) were randomly allotted to 4 treatments: basal diet (control, CON), 1% insoluble dietary fiber (IDF) diet, 1% soluble dietary fiber (SDF) diet, and 0.5% insoluble fiber + 0.5% soluble dietary fiber (MDF) diet. The trial lasted 28 days. SDF-fed piglets showed a higher (P < 0.05) bacterial a-diversity (observed_species, chao1, and ACE) and a higher relative abundance of Proteobacteria and Actinobacteria, Solobacterium, Succinivibrio, Blautia, and Atopobium in colonic digesta than CON, IDF, and MDF groups (P < 0.05). At the same time, Bacteroidetes, Euryarchaeota, Phascolarctobacterium, Coprococcus_1, and Prevotella_1 were significantly increased in the IDF group when compared with CON, SDF, and MDF groups (P < 0.05). Furthermore, Bacteroidetes and Enterobacteriaceae, Selenomonas, Phascolarctobacterium, and Alloprevotella(P < 0.05) were significantly higher in the MDF group than those in the other three groups (P < 0.05). SDF diet increased the concentrations of short-chain fatty acid (SCFA) in colonic digesta (P < 0.05) when compared with the CON group and enhanced weight index of the colon (P < 0.05) than the CON and IDF groups. Furthermore, compared with the CON group, SDF, IDF, and MDF diets all upregulated the mRNA expressions of claudin-1 (CLDN-1) in colonic mucosa (P < 0.05), SDF and IDF diets upregulated the mRNA expressions of mucin 2 (MUC2) (P < 0.05), SDF diet increased mRNA expressions of zonula occludens 1 (ZO-1) and occludin (OCLN), while the IDF group enhanced the secretory immunoglobulin A (sIgA) concentrations (P < 0.05), respectively. IDF and MDF diets decreased expressions of TNF-α(P < 0.05). We concluded that the influence of soluble fiber on colonic microbiota was more extensive than that of insoluble fiber. Moreover, soluble fiber could more effectively improve colonic barrier function by upregulating gene expressions of the gut barrier.

Consumo alimentar, estado nutricional e nível de atividade física em comunidade universitária brasileira

OBJETIVO: Este estudo teve como objetivo avaliar a variabilidade e a frequência do consumo alimentar, o estado nutricional e o nível de atividade física em uma comunidade universitária brasileira. MÉTODOS: A amostra constitui-se de 303 voluntários (130 homens e 173 mulheres) pertencentes à comunidade universitária do interior de São Paulo e avaliada por meio da disponibilização pela Internet do Questionário de Frequência Alimentar do International Physical Activity Questionaire e por meio da coleta da descrição autorreferida do peso e da altura. Foi realizada análise descritiva dos dados, análise de frequência alimentar e teste do coeficiente de correlação de Spearman. RESULTADOS: Foram observados inadequação dos hábitos alimentares, sobrepeso e obesidade na amostra estudada. As correlações entre os grupos alimentares apresentaram valores de magnitude maiores no grupo de mulheres que se alimentam de forma mais adequada do que os homens, mas não foram observadas diferenças entre os sexos no nível de atividade física. Não houve correlação significativa entre grupos de alimentos consumidos, índice de massa corporal e nível de atividade física em ambos os sexos. CONCLUSÃO: A comunidade universitária estudada apresentou baixo consumo de frutas, legumes e verduras, bem como consumo insuficiente de alimentos do grupo de cereais e leguminosas.

Stages of change for weight management in postpartum women

OBJECTIVE

This study examined factors related to stages of change for weight-management behaviors in postpartum women.

DESIGN

Cross-sectional data, collected at baseline, are reported from the Mothers' Overweight Management Study (MOMS), a randomized, controlled trial conducted in postpartum women who participated in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC).Subjects/Setting Subjects were a sample of WIC recipients (N=151) older than 18 years of age with a child younger than 2 years. Statistical analysis The dependent variables were the stages of change for weight-management behaviors (losing weight, avoiding high-fat foods, eating a high-fiber diet, and exercising). Demographic, health, and psychosocial variables were examined as independent variables. One-way analysis of variance was used to compare means, and chi(2) was used for proportions.

RESULTS

Whereas 55% of women were in the action stage for weight loss, fewer women were in the action stage for the following weight management behaviors: avoiding high-fat foods (24%), increasing fiber (19%), and exercising three times per week (29%). Identifying pros for weight management was related to stages for losing weight, high-fat food avoidance, and exercise (F=13.4, P<.001; F=10.5, P<.001; F=3.7, P<.007, respectively). Self-efficacy for choosing a low-fat restaurant meal or using food labels was positively related to later stages for avoiding high-fat foods and increasing fiber intake (chi(2)=16.4, P=.003; chi(2)=11.7, P=.02).

CONCLUSIONS

Emphasizing the pros for weight-management behaviors, decreasing the cons for exercising, increasing confidence to select low-fat restaurant choices, and improving skills for using food labels are four strategies that nutrition professionals can use to help women become more ready to change behaviors for weight management.

Glucose and insulin responses to a new zero-energy fiber source

OBJECTIVE

Consumption of a number of soluble fiber sources reduces glucose and insulin responses in humans. These fibers provide some available energy. Z-trim, a completely insoluble, noncaloric fiber/fat replacer produced from grain, was developed by ARS scientist George Inglett but until this report had not been tested in humans. The objective was to test the effects of consumption of various doses of this new fiber on glucose and insulin responses in humans.

DESIGN

Men and women (12 each) matched for age and body mass index (41 years, BMI 27) were given glucose or glucose with three levels of fiber in a Latin-square design. Blood samples were obtained before and 30, 60, 120 and 180 minutes after solutions containing glucose alone (1 g/kg body weight) and glucose plus 0.08, 0.17 and 0.33 g/kg body weight of Z-trim were consumed. Plasma glucose, insulin and glucagon were determined by enzyme or radioimmunoassays. A repeated-measures analysis of variance was conducted.

RESULTS

Glucose responses were lower for women than for men (p = 0.02) regardless of the test solution. At 30 minutes, glucose levels of men were 0.7-1.1 mmol/L lower after the two higher levels of fiber than after glucose alone. Insulin peak responses were delayed by high amounts of Z-trim. Fasting and response levels of glucagon were higher (p < 0.002) in women than in men. The decline in glucagon usually seen after a glucose load was moderated by the addition of fiber.

CONCLUSION

Although high levels of this new fiber may beneficially affect glucose metabolism of middle-aged people, it is less effective than soluble fiber.

Self-regulation training enhances dietary self-efficacy and dietary fiber consumption

OBJECTIVE

To evaluate the effectiveness of incorporating two self-regulation strategies (goal setting and self-monitoring) into a nutrition education class to enhance dietary fiber self-efficacy and foster a positive change in dietary fiber consumption.

DESIGN

College students in an introductory nutrition class (n = 113) were randomly assigned to one of four treatment conditions: goal setting, self-monitoring, goal setting and self-monitoring, and no goal setting and no self-monitoring. Twenty-six college students from an introductory health class served as the control group.

STATISTICAL ANALYSES

The main and interaction effects of goal setting and self-monitoring on postintervention variables were analyzed using analysis of covariance with baseline intake levels as the covariate. Analysis of variance was used to examine differences in the mean changes between the groups. Path analysis was conducted to analyze the causal linkage among the pretest and intervening variables to predict postintervention knowledge, self-efficacy, and fiber consumption.

RESULTS

Goal setting had a significant main effect on dietary fiber self-efficacy and on dietary fiber consumption Subjects who set goals scored 15% higher on the dietary fiber self-efficacy scale and consumed 91% more fiber than subjects who did not set goals. Self-monitoring had no significant main effect on either dietary fiber self-efficacy or dietary fiber consumption. There was no significant interaction between goal setting and self-monitoring. Changes in dietary fiber scores differed between the groups. Increases in dietary fiber for the goal setting and self-monitoring group were significantly higher than the goal-setting, self-monitoring, no goal setting and no self-monitoring, and control groups. In addition, the goal setting only group had significantly greater increases in fiber intake than the self-monitoring, no goal setting and no self-monitoring, and control groups. Changes in self-efficacy scores were significantly different between the groups. The goal setting and goal setting and self-monitoring groups had significantly higher self-efficacy scores than the control group. Path analysis revealed that both goal setting and self-monitoring affected dietary fiber consumption through knowledge and dietary fiber self-efficacy, goal setting had a strong direct effect on fiber consumption, and postintervention knowledge affected fiber consumption only through self-efficacy.

APPLICATIONS/CONCLUSIONS

Our findings suggest that dietary change requires active self-regulation of food intake. Combining goal setting and self-monitoring significantly enhances dietary behavior change. This strategy can easily be incorporated into nutrition education or counseling programs to enhance dietary behavior change.

Dietary intake as a cardiovascular risk factor in Costa Rican adolescents

PURPOSE

To evaluate Costa Rican adolescents' dietary intake as a cardiovascular disease (CVD) risk factor.

METHODS

Dietary intake was determined using 3-day food records; nutrient content of fast foods prepared in school cafeteria was calculated by the weighted records.

RESULTS

Around 30% of adolescents exceed the American Heart Association dietary recommendation for total fat and saturated fat. About 50% reported a cholesterol intake higher than 100 mg/1000 kcal. On average, 45% of adolescents do not meet the dietary fiber recommendation of 10 g/1000 kcal, the 66% of the recommended daily allowance for vitamins E and B(6), or around 25% for folic acid. A higher proportion of urban adolescents do not satisfy the established dietary recommendation to prevent CVD.

CONCLUSIONS

To avoid further increases in the Costa Rican CVD mortality rate, it is necessary to develop primary prevention programs, oriented to modify adolescent's nutrition habits. Schools have the potential to carry out such programs, as at least 60% of all adolescents in Costa Rica are enrolled in high schools.

Determination of total dietary fiber of intact cereal food products by near-infrared reflectance

Near-infrared reflectance spectra of cereal food products were acquired with a commercial dual-diode-array (Si, InGaAs) spectrometer customized to allow rapid acquisition of scans of intact breakfast cereals, snack foods, whole grains, and milled products. Substantial gains in the performance of multivariate calibration models generated from these data were obtained by a computational strategy that systematically analyzed the performance of various spectral windows. The calibration model based on 137 cereal food products determined the total dietary fiber (TDF) content of a test set of 45 intact diverse cereal food products with root-mean-squared error of cross-validation of between 1.8 and 2.0% TDF, relative to the laborious enzymatic-gravimetric reference method. The calibration performance is adequate to estimate TDF over the range of values found in diverse types of cereal food products (0.7-50.1%). The method requires no sample preparation and is relatively unaffected by specimen moisture content.

Nutrient intakes of senior women: balancing the low-fat message

Nutrient intakes based on six days of food intake were collected from 52 elderly Nova Scotian women. Mean reported energy intake was 1600 kilocalories, of which fat contributed 31%. Mean intakes of zinc and Vitamin D were below recommendations. Other nutrients of concern were protein, calcium, folate, and vitamins B6 and B12. Nutrition education efforts should be directed at assisting older people to maintain the generally recommended low fat intake, while stressing the desirability of a balanced food intake of sufficient quantity, which includes low-fat milk and dairy products, lean meats and legumes as sources of nutrients in low supply.

What is a high fiber diet?

There is no recognized definition of what constitutes a high fiber diet. Intakes of dietary fiber in different populations internationally vary widely from less than 20 g to more than 80 g per day. The types of foods contributing fiber also vary; in some countries cereals contribute the most fiber, in others leafy or root vegetables predominate. Vegetables have the highest fiber content per Kcal, and in most populations with fiber intakes over 50 g, vegetables contribute over 50% of total fiber intake. In rural Uganda, where the fiber hypothesis was first developed by Burkitt and Trowell, vegetables contribute over 90% of fiber intake. An experimental diet, the "Simian" diet, has been developed to mimic as closely as possible using human foods, the diet consumed by our simian ancestors the great apes. It is also similar to the Ugandan diet in containing large amounts of vegetables and 50 g fiber/1000 Kcal. Though nutritionally adequate, this diet is very bulky and not a suitable model for general recommendations. Dietary guidelines are that fat intake should be < 30% of energy, with a fiber intake of 20-35 g/d. These recommendations are inconsistent with a high fiber diet because, for people consuming more than about 2400 Kcal, low fiber choices for fruits and grains must be selected to keep dietary fiber intake within the range of 20-35 g. In a 30% fat, 1800 Kcal omnivorous diet, selection of wholemeal bread and whole fruit, results in a fiber intake over 35 g/d, and for and 1800 Kcal vegetarian diet, with substitution of modest amounts of peanut butter and beans for meats, dietary fiber intake goes up to 45 g/d. Thus, if it is desirable to promote the use of unrefined foods, the recommended dietary fiber intake should be a minimum of 15-20 g/1000 Kcal.

Dietary fiber values for various breads are higher using enzymatic analysis rather than detergent analysis

OBJECTIVE

To compare the dietary fiber content of breads commonly eaten in Georgia, Michigan, Nevada, and Vermont.

DESIGN

Dietary fiber content was determined according to neutral detergent fiber (NDF) plus pectin values and enzymatic gravimetric fiber values. White, whole-wheat, 100% stone-ground whole-wheat, cracked-wheat, and Roman Meal breads were analyzed for hemicellulose, cellulose, lignin, total NDF, pectin, and enzymatic gravimetric total fiber.

STATISTICAL ANALYSES PERFORMED

Analysis of variance was used to determine significant F tests, and individual means were compared using Duncan's multiple range test.

RESULTS

The 100% stone-ground whole-wheat bread had the most total fiber and fiber components followed by whole-wheat, Roman Meal, cracked-wheat, and white bread, except for pectin, of which Roman Meal had the most. The enzymatic gravimetric method of determining total fiber gave significantly (P < .0001) greater dietary fiber values than the values obtained by analyzing NDF plus pectin. These values ranged from 153% to 370% higher; however, there was a high degree of correlation (r = .95) between the methods.

CONCLUSIONS

When recommending types of breads, dietitians should be aware of added ingredients that influence fiber values. When using published fiber values, dietitians should consider the technique used to quantify the fiber content.