Biomedical subjects

Amy F Subar

Publications and source records attributed to Amy F Subar.

28 records · Page 2Linked to original sources

PubMed2003

Water turnover in 458 American adults 40-79 yr of age.

Despite recent interest in water intake, few data are available on water metabolism in adults. To determine the average and range of usual water intake, urine output, and total body water, we administered 2H oxide to 458 noninstitutionalized 40- to 79-yr-old adults living in temperate climates. Urine was collected in a subset of individuals (n = 280) to measure 24-h urine production using p-aminobenzoic acid to ensure complete collection. Preformed water intake was calculated from isotopic turnover and corrected for metabolic water and insensible water absorption from humidity. Preformed water intake, which is water from beverages and food moisture, averaged 3.0 l/day in men (range: 1.4-7.7 l/day) and 2.5 l/day in women (range: 1.2-4.6 l/day). Preformed water intake was lower in 70- to 79 (2.8 l/day)- than in 40- to 49-yr-old men and was lower in 70- to 79 (2.3 l/day)- than in 40- to 49- and 50- to 59-yr-old women. Urine production averaged 2.2 l/day in men (range: 0.6-4.9 l/day) and 2.2 l/day in women (0.9-6.0 l/day). There were no age-related differences in results in women, but 60- to 69-yr-old men had significantly higher urine output than 40- to 49- and 50- to 59-yr-old men. Only the 70- to 79-yr-old group included sufficient blacks for a racial analysis. Blacks in this age group showed significantly lower preformed water intake than did whites. Whites had significantly higher water turnover rates than blacks as well. Multivariate regression indicated that age, weight, height, and body mass index explained <12% of the gender-specific variance in water input or urine output, yet repeat measures indicated that within-individual coefficient of variation was 8% for preformed water intake (n = 22) and 9% for 24-h urine production (n = 222). These results demonstrate that water turnover is highly variable among individuals and that little of the variance is explained by anthropometric parameters.

4-Aminobenzoic Acid↗

PubMed2003

Structure of dietary measurement error: results of the OPEN biomarker study.

Multiple-day food records or 24-hour dietary recalls (24HRs) are commonly used as "reference" instruments to calibrate food frequency questionnaires (FFQs) and to adjust findings from nutritional epidemiologic studies for measurement error. Correct adjustment requires that the errors in the adopted reference instrument be independent of those in the FFQ and of true intake. The authors report data from the Observing Protein and Energy Nutrition (OPEN) Study, conducted from September 1999 to March 2000, in which valid reference biomarkers for energy (doubly labeled water) and protein (urinary nitrogen), together with a FFQ and 24HR, were observed in 484 healthy volunteers from Montgomery County, Maryland. Accounting for the reference biomarkers, the data suggest that the FFQ leads to severe attenuation in estimated disease relative risks for absolute protein or energy intake (a true relative risk of 2 would appear as 1.1 or smaller). For protein adjusted for energy intake by using either nutrient density or nutrient residuals, the attenuation is less severe (a relative risk of 2 would appear as approximately 1.3), lending weight to the use of energy adjustment. Using the 24HR as a reference instrument can seriously underestimate true attenuation (up to 60% for energy-adjusted protein). Results suggest that the interpretation of findings from FFQ-based epidemiologic studies of diet-disease associations needs to be reevaluated.

Adult↗

PubMed2003

Using intake biomarkers to evaluate the extent of dietary misreporting in a large sample of adults: the OPEN study.

This paper describes the Observing Protein and Energy Nutrition (OPEN) Study, conducted from September 1999 to March 2000. The purpose of the study was to assess dietary measurement error using two self-reported dietary instruments-the food frequency questionnaire (FFQ) and the 24-hour dietary recall (24HR)-and unbiased biomarkers of energy and protein intakes: doubly labeled water and urinary nitrogen. Participants were 484 men and women aged 40-69 years from Montgomery County, Maryland. Nine percent of men and 7% of women were defined as underreporters of both energy and protein intake on 24HRs; for FFQs, the comparable values were 35% for men and 23% for women. On average, men underreported energy intake compared with total energy expenditure by 12-14% on 24HRs and 31-36% on FFQs and underreported protein intake compared with a protein biomarker by 11-12% on 24HRs and 30-34% on FFQs. Women underreported energy intake on 24HRs by 16-20% and on FFQs by 34-38% and underreported protein intake by 11-15% on 24HRs and 27-32% on FFQs. There was little underreporting of the percentage of energy from protein for men or women. These findings have important implications for nutritional epidemiology and dietary surveillance.

Adult↗

PubMed2003

Dietary fibre and colorectal adenoma in a colorectal cancer early detection programme.

BACKGROUND: Although dietary fibre has been reported to have no association with colorectal adenoma and cancer, in some studies this topic remains controversial. METHODS: We used a 137-item food frequency questionnaire to assess the relation of fibre intake and frequency of colorectal adenoma. The study was done within the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, a randomised controlled trial designed to investigate methods for early detection of cancer. In our analysis, we compared fibre intake of 33971 participants who were sigmoidoscopy-negative for polyps, with 3591 cases with at least one histologically verified adenoma in the distal large bowel (ie, descending colon, sigmoid colon, or rectum). Odds ratios were estimated by logistic regression analysis. FINDINGS: High intakes of dietary fibre were associated with a lower risk of colorectal adenoma, after adjustment for potential dietary and non-dietary risk factors. Participants in the highest quintile of dietary fibre intake had a 27% (95% CI 14-38, p(trend)=0.002) lower risk of adenoma than those in the lowest quintile. The inverse association was strongest for fibre from grains and cereals and from fruits. Risks were similar for advanced and non-advanced adenoma. Risk of rectal adenoma was not significantly associated with fibre intake. INTERPRETATION: Dietary fibre, particularly from grains, cereals, and fruits, was associated with decreased risk of distal colon adenoma.

Adenoma↗

PubMed2003

Comparison of estimated renal net acid excretion from dietary intake and body size with urine pH.

OBJECTIVE: The aim of this study was to examine whether estimated net acid excretion (NAE) from two dietary assessment instruments can predict urine pH in healthy volunteers. DESIGN: The Observing Protein and Energy Nutrition (OPEN) study, which was designed to assess dietary measurement error, included men and women aged 40 to 69 years. Participants were asked to complete two food frequency questionnaires (FFQs) and two 24-hour recalls at approximately three-month intervals, and to return two 24-hour urine samples during the same period. NAE was estimated using a previously described equation. The estimates obtained from the different dietary assessment measures were correlated with actual urine pH. SUBJECTS/SETTING: Four hundred eighty-four subjects were enrolled in the OPEN study. All participants were included in this study on urine pH, given that they had all completed at least one dietary assessment and one urine sample. The study took place in Montgomery County, MD, between September 1999 and March 2000. RESULTS: Correlation coefficients between NAE estimates using the FFQ data and the average of two urine pH measures were -0.34 and -0.39 for women and men, respectively. Removing within-person variance in the urine pH levels resulted in a deattenuated overall correlation of -0.50 for the FFQ. Correlations between the 24-hour recall estimates of NAE were -0.41 and -0.32 for women and men, respectively. For the 24-hour recalls, the deattenuated overall correlation was -0.50. APPLICATION/CONCLUSIONS: Our findings suggest that FFQs provide adequate dietary data to estimate renal NAE and could be used as a surrogate for urinary pH levels in large epidemiologic studies.

Acids↗

PubMed2003

A comparison of a food frequency questionnaire with a 24-hour recall for use in an epidemiological cohort study: results from the biomarker-based Observing Protein and Energy Nutrition (OPEN) study.

BACKGROUND: Most large cohort studies have used a food frequency questionnaire (FFQ) for assessing dietary intake. Several biomarker studies, however, have cast doubt on whether the FFQ has sufficient precision to allow detection of moderate but important diet-disease associations. We use data from the Observing Protein and Energy Nutrition (OPEN) study to compare the performance of a FFQ with that of a 24-hour recall (24HR). METHODS: The OPEN study included 484 healthy volunteer participants (261 men, 223 women) from Montgomery County, Maryland, aged 40-69. Each participant was asked to complete a FFQ and 24HR on two occasions 3 months apart, and a doubly labelled water (DLW) assessment and two 24-hour urine collections during the 2 weeks after the first FFQ and 24HR assessment. For both the FFQ and 24HR and for both men and women, we calculated attenuation factors for absolute energy, absolute protein, and protein density. RESULTS: For absolute energy and protein, a single FFQ's attenuation factor is 0.04-0.16. Repeat administrations lead to little improvement (0.08-0.19). Attenuation factors for a single 24HR are 0.10-0.20, but four repeats would yield attenuations of 0.20-0.37. For protein density a single FFQ has an attenuation of 0.3-0.4; for a single 24HR the attenuation factor is 0.15-0.25 but would increase to 0.35-0.50 with four repeats. CONCLUSIONS: Because of severe attenuation, the FFQ cannot be recommended as an instrument for evaluating relations between absolute intake of energy or protein and disease. Although this attenuation is lessened in analyses of energy-adjusted protein, it remains substantial for both FFQ and multiple 24HR. The utility of either of these instruments for detecting important but moderate relative risks (between 1.5 and 2.0), even for energy-adjusted dietary factors, is questionable.

Adult↗

PubMed2002

Cognitive research enhances accuracy of food frequency questionnaire reports: results of an experimental validation study.

OBJECTIVE: To test whether changing a food frequency questionnaire (FFQ) on the basis of cognitive theory and testing results in greater accuracy. Accuracy was examined for 4 design issues: a) Grouping: asking about foods in a single vs multiple separate questions; b) different forms of a food: asking consumption frequency of each form of a food (eg, skim, 2%, whole milk) vs a nesting approach--asking frequency of the main food (eg, milk) and proportion of times each form was consumed; c) additions (eg, sugar to coffee): asking independent of the main food vs nested under the main foods; d) units: asking frequency and portion size vs frequency of units (eg, cups of coffee). DESIGN: Participants in two randomly assigned groups completed 30 consecutive daily food reports (DFRs), followed by 1 of 2 FFQs that asked about foods consumed in the past month. One was a new, cognitively-based National Cancer Institute (NCI) Diet History Questionnaire; the other was the 1992 NCI-Block Health Habits and History Questionnaire. SUBJECTS/SETTING: 623 participants, age range 25 to 70 years, from metropolitan Washington, DC. Statistical analyses performed Accuracy was assessed by comparing DFR and FFQ responses using categorical (percent agreement) and continuous (rank order correlation, discrepancy scores) agreement statistics. RESULTS: Grouping: accuracy was greater using separate questions. Different forms of food: accuracy was greater using nesting. Additions: neither approach was consistently superior; accuracy of the addition report was affected by accuracy of the main food report. Units: both approaches were similarly accurate. CONCLUSIONS: Accuracy of FFQ reporting can be improved by restructuring questions based on cognitive theory and testing.

Adult↗

PubMed2002

Changes in vegetable and fruit consumption and awareness among US adults: results of the 1991 and 1997 5 A Day for Better Health Program surveys.

OBJECTIVE: The purpose of this study is to assess population-based changes in vegetable and fruit consumption and psychosocial correlates. DESIGN: Two nationally representative random digit dial surveys conducted in 1991 and 1997; respondents were queried regarding consumption of and attitudes and knowledge about vegetables and fruit. SUBJECTS/SETTING: Respondents were 2,755 and 2,544 adults (in 1991 and 1997, respectively) older than 18 years. STATISTICAL ANALYSIS PERFORMED: Vegetable and fruit consumption and message awareness were measured using weighted-only and regression model-adjusted analyses to assess changes. RESULTS: Mean vegetable and fruit consumption was significantly (P=.007) higher in 1997 than in 1991 using weighted-only analyses, but remained significant only for Hispanic (P=.03) and nonsmoker (P=.004) subgroups when adjusted for demographic shifts. Significantly higher percentages were found in the model-adjusted analyses for those consuming 5 or more (daily servings (23.4% to 25.8%), message awareness (7.7% to 19.2%), and knowledge of the 5 A Day Program (2.0% to 17.8%). APPLICATIONS/CONCLUSIONS: A significantly positive change in vegetable and fruit consumption occurred between 1991 and 1997 according to traditional methods of survey data analysis, but null findings resulted when the data were adjusted for demographic shifts. Nutrition professionals should continue targeting specific demographic subgroups with tailored interventions to move all Americans toward achievement of dietary guidelines for vegetable and fruit consumption.

Adult↗

PubMed2002

Fruit and vegetable assessment: performance of 2 new short instruments and a food frequency questionnaire.

OBJECTIVE: To evaluate the ability of 2 new short assessment instruments and a food frequency questionnaire (FFQ) to measure intake of fruit and vegetables. The "All-Day" screener asks frequency and portion size questions about 9 food items. The "By-Meal" screener is similar, except that it asks about 2 of those 9 food items in terms of mealtime. DESIGN: Survey participants completed 4 telephone-administered 24-hour dietary recalls over 1 year, a self-administered FFQ 1 to 2 months later, and 1 of 2 self-administered screeners after an additional 7 months. SUBJECTS/SETTING: Participating were 202 men and 260 women aged 20 to 70 years living throughout the United States. STATISTICAL ANALYSES: Fruit and vegetable intakes measured by each screener and the FFQ were compared with true usual intake based on a measurement error model with 24-hour dietary recalls as the reference instrument. RESULTS: Estimates of median daily servings of fruit and vegetables were as follows: For men: True intake (5.8) vs All-Day screener (5.0), By-Meal screener (5.5), and FFQ (6.6); for women: true intake (4.2) vs All-Day screener (5.0), By-Meal screener (5.4), and FFQ (6.2). Estimated correlations between the test instruments and true intake were as follows: For men: All-Day screener (0.66), By-Meal screener (0.67), FFQ (0.68); for women: All-Day screener (0.51), By-Meal screener (0.53), and FFQ (0.54). APPLICATIONS/CONCLUSIONS: Both screeners might be useful to estimate median intakes of fruit and vegetable servings in US populations, but they might be less useful in accurately ranking individuals. More research is needed before using the screeners in ethnic or low-literacy populations.

Adult↗

PubMed2002

Fruit and vegetable intakes and the risk of colorectal cancer in the Breast Cancer Detection Demonstration Project follow-up cohort.

BACKGROUND: Recent findings have cast doubt on the hypothesis that high intakes of fruit and vegetables are associated with a reduced risk of colorectal cancer. OBJECTIVE: In a large prospective cohort of women, we examined the association between fruit and vegetable intakes and colorectal cancer. DESIGN: Between 1987 and 1989, 45490 women with no history of colorectal cancer satisfactorily completed a 62-item Block-National Cancer Institute food-frequency questionnaire. During 386142 person-years of follow-up, 314 women reported incident colorectal cancer, searches of the National Death Index identified an additional 106 colorectal cancers, and a match with state registries identified another 65 colorectal cancers for a total of 485 cases. We used Cox proportional hazards regression analysis to estimate the relative risks (RRs) and 95% CIs in both energy-adjusted and fully adjusted models. RESULTS: In models using the multivariate nutrient-density model of energy adjustment, RRs for increasing quintile of fruit consumption indicated no significant association with colorectal cancer [RR (95% CI)]: 1.00 (reference), 0.94 (0.70, 1.26), 0.85 (0.63, 1.15), 1.07 (0.81, 1.42), and 1.09 (0.82, 1.44). For vegetable consumption, there was also no significant association in the multivariate nutrient-density model with increasing quintiles of consumption: 1.00 (reference), 0.77 (0.58, 1.02), 0.83 (0.63, 1.10), 0.90 (0.69, 1.19), and 0.92 (0.70, 1.22). Additionally, 3 alternative models of energy adjustment showed no significant association between increases in vegetable intake and the risk of colorectal cancer. CONCLUSION: Although the limitations of our study design and data merit consideration, this investigation provides little evidence of an association between fruit and vegetable intakes and colorectal cancer.

Cohort Studies↗