Methodologic issues for pooling dietary data

Evaluating energy intake measurement in free-living subjects: when to record and for how long?

OBJECTIVE

To nutritionally analyse mean energy intake (EI) from different 3 d intervals within a 7 d recording period and to evaluate the seasonal effect on energy and nutrient intake.

DESIGN

Cross-sectional study of dietary intake collected with 7 d food diaries.

SETTING

Aberdeen, north-east Scotland, UK, between 2002 and 2004.

SUBJECTS

Participants from two long-term trials were pooled. These trials, investigating genetic and environmental influences on body weight, were the Genotyping And Phenotyping (GAP) study and a cohort observational study, Rowett Assessment of Childhood Appetite and metaboLism (RASCAL). There were 260 Caucasian adults, BMI range 16.7-49.3 kg/m2, age range 21-64 years.

RESULTS

Mean EI for Wednesday, Friday and Saturday had the closest approximation to the 7 d mean (0.1 % overestimate). A gender x season interaction (P = 0.019) with a different intake pattern for females and males was observed. For females, lower mean (se) EI was recorded in summer (8117 (610) kJ) and autumn (7941 (699) kJ) compared with spring (8929 (979) kJ) and winter (8132 (1041) kJ). For males, higher mean (se) EI was recorded in summer (10 420 (736) kJ) and autumn (10 490 (1041) kJ) compared with spring (9319 (1441) kJ) and winter (9103 (1505) kJ).

CONCLUSIONS

The study results indicate that 3 d weighed intakes recorded from Wednesday, Friday and Saturday are most representative of 7 d habitual intake in free-living subjects. They also indicate that seasonality has a limited effect on EI and no effect on macronutrient intake.

Relative validity of a semiquantitative food frequency questionnaire designed for schoolchildren in western Greece

Background

The use of food frequency questionnaires (FFQs) has become increasingly important in epidemiologic studies. During the past few decades, a wide variety of nutritional studies have used the semiquantitative FFQ as a tool for assessing and evaluating dietary intake. One of the main concerns in a dietary analysis is the validity of the collected dietary data.

Methods

This paper discusses several methodological and statistical issues related to the validation of a semiquantitative FFQ. This questionnaire was used to assess the nutritional habits of schoolchildren in western Greece. For validation purposes, we selected 200 schoolchildren and contacted their respective parents. We evaluated the relative validity of 400 FFQs (200 children's FFQs and 200 parents' FFQs).

Results

The correlations between the children's and the parents' questionnaire responses showed that the questionnaire we designed was appropriate for fulfilling the purposes of our study and in ranking subjects according to food group intake.

Conclusion

Our study shows that the semiquantitative FFQ provides a reasonably reliable measure of dietary intake and corroborates the relative validity of our questionnaire.

Relationship between nutritional habits adopted by ulcerative colitis relevant to cancer development patients at clinical remission stages and molecular-genetic parameters

UC (ulcerative colitis) patients have an increased risk of developing colorectal cancer compared with the normal population. The cause underlying this higher risk is not fully defined but includes nutritional and environmental factors concomitant with genetic alterations. We aimed to evaluate genetic stability in the colonic tissue of UC patients in clinical remission compared with the healthy population, and to establish a possible correlation between nutritional habits and these molecular assessments. UC patients (n 42) and healthy controls (n 37) participated in the study. All participants were histopathologically and medically diagnosed. Participants completed five separate 7 d dietary records, food-frequency questionnaires and validated 24 h recalls for nutritional assessment. The extent of chromosome 17 loss and the calculated chromosome index was determined in colon tissue biopsies by fluorescence in situ hybridisation. Correlations between the molecular and nutritional assessments were performed using Pearson's correlation coefficients. Significant differences in the nutritional intake of total fat (65 (SD 15) v. 89 (SD 25) g), cholesterol (330 (SD 168) v. 464 (SD 177) mg), dietary fibre (32 (SD 4.7) v. 9 (SD 4) g), vitamin A (1009 (SD 209) v. 506 (SD 204) microg), vitamin C (308 (SD 108) v. 72 (SD 53) mg) and folic acid (412 (SD 89 microg) v. 187 (SD 107)) were recorded for UC patients compared with controls. Significant correlations were found for the consumption of different food groups and the chromosome index for chromosome 17. The results of our study suggest that the nutritional habits adopted by UC patients during clinical remission may affect key cellular components of the colonic tissue, inducing a high degree of aneuploidy and genetic instability, and probably affecting the development of colon cancer.

European Prospective Investigation into Cancer and Nutrition (EPIC) calibration study: rationale, design and population characteristics

The European Prospective Investigation into Cancer and Nutrition (EPIC), which covers a large cohort of half a million men and women from 23 European centres in 10 Western European countries, was designed to study the relationship between diet and the risk of chronic diseases, particularly cancer. Information on usual individual dietary intake was assessed using different validated dietary assessment methods across participating countries. In order to adjust for possible systematic over- or underestimation in dietary intake measurements and correct for attenuation bias in relative risk estimates, a calibration approach was developed. This approach involved an additional dietary assessment common across study populations to re-express individual dietary intakes according to the same reference scale. A single 24-hour diet recall was therefore collected, as the EPIC reference calibration method, from a stratified random sample of 36 900 subjects from the entire EPIC cohort, using a software program (EPIC-SOFT) specifically designed to standardise the dietary measurements across study populations. This paper describes the design and populations of the calibration sub-studies set up in the EPIC centres. In addition, to assess whether the calibration sub-samples were representative of the entire group of EPIC cohorts, a series of subjects' characteristics known possibly to influence dietary intakes was compared in both population groups. This was the first time that calibration sub-studies had been set up in a large multi-centre European study. These studies showed that, despite certain inherent methodological and logistic constraints, a study design such as this one works relatively well in practice. The average response in the calibration study was 78.3% and ranged from 46.5% to 92.5%. The calibration population differed slightly from the overall cohort but the differences were small for most characteristics and centres. The overall results suggest that, after adjustment for age, dietary intakes estimated from calibration samples can reasonably be interpreted as representative of the main cohorts in most of the EPIC centres.

Vitamins in Spanish food patterns: the eVe Study

OBJECTIVE

To describe vitamin intakes in Spanish food patterns, identify groups at risk for inadequacy and determine conditioning factors that may influence this situation.

DESIGN

Pooled-analysis of eight cross-sectional regional nutrition surveys.

SUBJECTS

Ten thousand two hundred and eight free-living subjects (4728 men, 5480 women) aged 25-60 years. Respondents of population nutritional surveys carried out in eight Spanish regions (Alicante, Andalucia, Balearic Islands, Canary Islands, Catalunya, Galicia, Madrid and Basque Country) from 1990 to 1998. The samples were pooled together and weighted to build a national random sample.

METHODS

Dietary assessment by means of repeated 24-hour recall using photograph models to estimate portion size. Adjusted data for intra-individual variation were used to estimate the prevalence of inadequate intake. A Diet Quality Score (DQS) was computed considering the risk for inadequate intake for folate, vitamin C, vitamin A and vitamin E. DQS scores vary between 0 (good) and 4 (very poor). Influence of lifestyle (smoking, alcohol consumption and physical activity) was considered as well.

RESULTS

Inadequate intakes (<2/3 Recommended Dietary Intake) were estimated in more than 10% of the sample for riboflavin (in men), folate (in women), vitamin C, vitamin A, vitamin D and vitamin E. More than 35% of the sample had diets classified as poor quality or very poor quality. Factors identified to have an influence on a poor-quality diet were old age, low education level and low socio-economical level. A sedentary lifestyle, smoking, usual consumption of alcohol and being overweight were conditioning factors for a poor-quality diet as well.

CONCLUSION

Results from The eVe Study suggest that a high proportion of the Spanish population has inadequate intakes for at least one nutrient and nearly 50% should adjust their usual food pattern towards a more nutrient-dense, healthier diet.