Validation with biological markers for food intake of a dietary assessment method used by Swedish women with three different dietary preferences.

OBJECTIVES: To validate a dietary assessment method, a 4-day food record together with a duplicate portion technique, with biological markers for food intake.
DESIGN: Four days of duplicate portions were collected in parallel with food recording. A 24-h urine sample and the faeces corresponding to the food intake (using a coloured marker) were collected. Completeness of urine and faeces collections was assessed using para-aminobenzoic acid (PABA) in urine and cadmium in faeces, respectively. Biomarkers of food intake (energy, protein, fibre, sodium, potassium, calcium) were measured in urine and faeces.
SETTING: Swedish west coast.
SUBJECTS: Non-smoking Swedish women, 20-50 years of age, consuming a mixed diet (n = 34), a mixed diet rich in shellfish (n = 17) or a vegetarian/high-fibre diet (n = 23).
RESULTS: The average ratio (food intake according to the dietary assessment methods/ biological marker) for protein, sodium, potassium and calcium was 0.86. This indicates an underestimation of the food intake by approximately 15%. The ratio of stated fibre intake to biological marker was 1.20 for the mixed diet and the vegetarian diet group, indicating an overestimation by approximately 20%.
CONCLUSIONS: The underestimation of the intake of protein, sodium, potassium and calcium by all three groups and the overestimation of the fibre intake by two groups indicate that underreporting is selective to certain nutrients and foods and to various groups of people. The two dependent dietary assessment methods were equally good in measuring protein intake, which indicates that the women recorded what they actually duplicated.