Interpretation Of Dietary Data Research Articles

A Prospective Cohort Study of Substitutions of Poultry, Red Meat or Lean Fish with Fatty Fish and the Risk of Incident Peripheral Arterial Disease in Men

Introduction - The evidence regarding potential associations between intake of fish, poultry, red meat and the risk of peripheral arterial disease (PAD) is limited. Analysis and interpretation of dietary data are difficult. First, most foods are eaten together with foods characteristic for the dish and secondly, increased consumption of one food type is typically accompanied by a lower intake of other food types. To account for this we used the substitution approach in which we compare individuals with different food patterns corresponding to replacing one food item with another. The aims of this study were to examine associations for substitutions of poultry, red meat and lean fish with fatty fish and the risk of PAD. We hypothesised that a higher intake of fatty fish and a concomitant lower intake of other meat products was associated with a lower risk of PAD. Methods - We conducted a prospective cohort study based on data from the Diet, Cancer and Health cohort initiated in 1993 to 1997. At baseline, middle-aged men filled in a lifestyle questionnaire and a validated 192-item semi-quantitative food frequency questionnaire about their usual diet the year before. During follow-up, we identified participants with validated diagnoses of peripheral arterial disease with ankle-brachial index below 90% or toe-brachial index below 70%. Data were analysed using multivariable Cox regression models. Substitutions of 150 g/week of either poultry, processed red meat, unprocessed red meat or lean fish with 150 g/week of fatty fish were explored. Results - After relevant exclusions and follow-up for a median of 13.6 years, 546 eligible PAD cases were identified in the cohort of 25,725 men. In multivariable analyses including adjustment for established lifestyle risk factors for PAD, the HR of replacing poultry with fatty fish was 0.93 (95% CI 0.77-1.11), while the HRs of incident PAD after replacing either unprocessed or processed red meat with fatty fish were 0.88 (95% CI 0.76-1.03) and 0.85 (95% CI 0.73-1.00), respectively. When substituting lean fish with fatty fish the HR of PAD was 0.89 (95% CI 0.72-1.11). The associations were all in the same direction, however not statistically significant.Table 1Substitution between 150 g per week of different meat and the risk of peripheral arterial diseaseSubstitution between food groups per 150 g/weekHR∗95% CIHR∗∗95% CIFatty fish instead of poultry1.00(0.83-1.21)0.93(0.77-1.11)Fatty fish instead of unprocessed red meat0.85(0.73-0.99)0.88(0.76-1.03)Fatty fish instead of processed red meat0.76(0.65-0.89)0.85(0.73-1.00)Fatty fish instead of lean fish0.85(0.69-1.06)0.89(0.72-1.11)*Model 1A: Crude analysis adjusted for age and energy intake.**Model 1B: As model 1A with additional adjustment for traditional risk factors including educational level, BMI, waist circumference, physical activity, alcohol intake and smoking. Open table in a new tab *Model 1A: Crude analysis adjusted for age and energy intake. **Model 1B: As model 1A with additional adjustment for traditional risk factors including educational level, BMI, waist circumference, physical activity, alcohol intake and smoking. Conclusion - This study suggested that substituting meat products and lean fish with fatty fish might be associated with a lower risk of incident PAD, however not statistically significant.

Interpretation of data on dietary intake.

Although this discussion has focused on the interpretation of dietary data, assuming that it is representative of actual and usual intake and that the nutrient analysis based on it involved the use of up-to-date food composition tables, the readers should be sensitive to other potential sources of error or bias in obtaining information on food and/or nutrient intake. These include errors due to irregularity of food consumption, under- or overreporting of intake, errors in reporting either the amount or the description of the food consumed, recording errors on the part of the interviewer or coding errors on the part of the coder, limitations in the tables of food composition due to missing data for certain nutrients in certain foods or to biologic variability in the same foods from different sources or in those marketed under different conditions, imputed values, the unknown composition of formulated foods or foods prepared from home or commercial recipes, differences in bioavailability of nutrients as a function of the diet, or the use of abridged tables of food composition. In spite of the many unresolved issues relating to dietary standards and the interpretation of dietary intake data, we are still able to make a reasonable assessment of dietary adequacy of groups and individuals with our current system, which is viewed as a unique federal resource. It is hoped that the eventual passage of the National Nutrition Monitoring and Related Research Act will provide both the impetus and the resources to permit us to develop a more sophisticated system for assessing both food intake and nutritional status.

Primary dietary prevention: Is the fiber story over?

Colorectal cancer is a major cause of morbidity in developed countries, and epidemiological and experimental research suggests that environmental factors, particularly diet, may play a key etiologic role. Among the various dietary factors that have been proposed to affect the risk and progression of colon cancer, dietary fiber has been of greatest interest, due to the effects of fiber on the function of the large bowel. Dietary fiber is a heterogeneous group of compounds, consisting of the remnants of plant cells resistant to hydrolysis by human alimentary enzymes. Several case-control studies and a few cohort studies have linked higher fiber intake to reduced risk for colorectal cancer, although the results of these observational studies have been inconsistent. In the large European Prospective Investigation into Cancer and Nutrition observational study, higher dietary fiber from foods was associated with an estimated 25% reduction in risk for large bowel cancer. However, no significant relationship between fiber intake (or major food sources of fiber) and risk for colorectal cancer was observed in a recently reported large pooled analysis of several cohort studies. Well-known limitations of observational studies, particularly relating to the collection and interpretation of dietary data, constrain conclusions from these studies. To date, intervention studies testing the relationship between dietary fiber and colon cancer have focused on whether fiber supplementation or diet modification can affect the risk for adenoma recurrence and growth in individuals with a history of adenomatous polyps. In four of these intervention studies, subjects in the intervention arm were prescribed dietary fiber supplements, and beneficial effects on adenoma recurrence were not observed over 3-5 years of follow-up. In a large randomized U.S. study, the Polyp Prevention Trial, the effect of prescribing diet modification (increased fiber and reduced fat intakes) was tested, and no effects on adenoma recurrence were observed, although dietary biomarker data suggest that the change in dietary intakes in the intervention arm was not substantial. The effect of increased dietary fiber intake on risk for colorectal cancer has not been adequately addressed in studies conducted to date. Longer-term trials and higher levels of fi- ber intake are strategies that have been suggested to increase knowledge in this area. Also, laboratory and clinical studies that continue to provide insight into biological mechanisms may help to better target intervention efforts.

The influence of survey duration on estimates of food intakes--relevance for food-based dietary guidelines.

Development of food-based dietary guidelines relies on correct identification and interpretation of current dietary intake patterns. The process involves assessing which foods discriminate between those with desirable and undesirable intakes of particular nutrients. It is therefore important that those involved in this task are aware of any source of variability in the underlying food consumption data that cannot be attributed to true differences between individuals. A short survey duration can introduce a high degree of within-person variation and not reflect usual or more long-term food or nutrient intakes. As survey duration increases, the % consumers identified by a survey increases and the intakes among consumers only decrease while the total population intakes do not change. A short survey duration may also lead to misclassification of individuals into high and low consumers. Survey duration is therefore an issue that should be considered in the interpretation of dietary data when developing food-based dietary guidelines.

Under- and overreporting of energy intake related to weight status and lifestyle in a nationwide sample

Desire for weight change and level of dietary consciousness may severely bias reported food intake in dietary surveys. We evaluated to what degree under- and overreporting of energy intake (EI) was related to lifestyle, sociodemographic variables, and attitudes about body weight and diet in a nationwide dietary survey. Data were gathered by a self-administered quantitative food-frequency questionnaire distributed to a representative sample of men and women aged 16-79 y in Norway, of whom 3144 subjects(63%) responded. Reported EI was related to estimated basal metabolic rate (BMR) based on self-reported body weight, age, and sex. An EI:BMR <1.35 was considered to represent underreporting and an EI:BMR > 2.4 as overreporting of EI. Fewer men than women underreported EI (38% compared with 45%). The fraction of overreporters did not differ significantly between sexes (7% of the men compared with 5% of the women). A large proportion of underreporters was obese (9%) and wanted to reduce their weight (41%). Few overreporters were obese and 12% wanted to increase their weight. Underreporters consumed fewer foods rich in fat and sugar than did the other subjects. Multiple regression analysis showed that desire for weight change and physical activity score were significantly correlated with both EI and EI:BMR when adjusted for sociodemographic and lifestyle variables. Our findings indicated that attitudes about one’s own body weight influenced reported EI. These attitudes are important in the interpretation of dietary data because many of the subjects (>30%) wanted to change their body weight. Am J Clin Nutr 1998;68:266–74.

Assessing the nation’s diet: Limitations of the fool frequency questionnaire

Assessment of the diet of the US population is important for nutrition monitoring and policy-making and for planning health promotion and disease prevention activities. Accurate information about food and nutrient intake is critical to monitoring the dietary and nutritional status of the general population and subgroups at nutritional risk. The selection and proper use of dietary methods to measure intake and the appropriate interpretation of dietary data are central to the assessment of the population's dietary intake

Guidelines for use of dietary intake data

This article presents the guidelines from the report of the ad hoc Expert Panel on Guidelines for Use of Dietary Intake Data. The report was prepared under terms of a contract with the Life Sciences Research Office of the Federation of American Societies for Experimental Biology to provide the Food and Drug Administration with a working reference for evaluating dietary intake data. The guidelines represent the Expert Panel's conclusions on appropriate ways to interpret dietary data relating to (a) prevalence of consumption of particular levels of foods or food components, (b) comparisons of intake of different groups within the U.S. population, (c) time trends in consumption of foods or food components, and (d) relationships of intake of a food or food component to a given health outcome. The guidelines address general issues concerning dietary data collection and statistical concerns as well as specific issues important in interpretation of dietary data. J Am Diet Assoc 88:1258, 1988.

Some difficulties inherent in the interpretation of dietary data from free-living populations

Isocaloric adjustments of diet in metabolic experiments tend to induce negative correlations. In free-living populations, on the other hand, the absolute amounts of major nutrients consumed are positively correlated with total calorie intake and with each other. In general, these positive correlations are fairly strong. Relative amounts of nutrients consumed tend to be weakly and negatively correlated with total calories and each other. Because of these intercorrelations conclusions drawn from cross-sectional population data are ambiguous, at best, and misleading, at worst. Beyond that, the correlation between the intakes of specific nutrients with total calorie intake introduces the possibility that dietary variables may to some degree be surrogates of some nondietary variables; in particular, of physical activity. Unless the questions being asked in population studies are precisely formulated, with a careful consideration of the biological issues and the statistical limitations, biased conclusions are likely to result.