Publication Details

Charlton, K. E. & Lambert, E. V. 1999, 'Validation of a food frequency questionnaire in older South Africans', SAMJ South African Medical Journal, vol. 89, no. 2, pp. 184-189.


Objectives: To assess the validity of 213-item semi-qualified food frequency questionnaire (FFQ) in estimating habitual energy and protein intake in a sample of older South Africans. Repeatability of the FFQ was assessed by comparison of reported intakes after a 6-month period. Design: Cross-sectional analytic study Methods: Twenty-one subjects were selected from a baseline sample of 200 non-institutional subjects aged 65 years and over in Cape Town, who had previously been randomly selected for a nurtition and health survey using a two-stage cluster design. Reported dietary energy and protein intakes, estimated by means of the FFQ method, were compared with 24-hour energy expenditure, measured by the heart-rate monitoring technique and 24 hour urinary nitrogen excretion, respectively. Results: Spearman correlation coefficients for reported energy intake (using the FFQ) versus measured energy expenditure were 0.31 (P=0.482) and 0.36 (P=0.35) for men and women, respectively. Men tended to underreport energy intake, while women tended systematically to overestimate energy intake by 21% and 25%, respectively. In men, reported protein intake using the FFQ closely matched urinary protein excretion and a good association between the two measures was found (r=0.62; P=0.061). In women, no association was found between reported protein intake and urinary nitrogen excretion. The FFQ resulted in a twofold overestimate of protein intake, based on urinary nitrogen excretion. In women, correlations between 6-month repeated measures of energy and protein intake using the FFQ were 0.69 (P=0.067) and 0.61 (P=0.053), respectively; however a poor between measure association was found in men. Conclusions: The study findings demonstrate that the semi-quantified FFQ method underestimated food energy intake in older men and overestimated both energy and protein intake in older women.