Abstract:
It is now widely recognized that reported energy intakes in dietary surveys underestimate usual
energy intake (Black et al., 1993). During this study specific subject characteristics contributing to
underreporting and the possible association between the metabolic syndrome and underreporting
were investigated.
A multi-disciplinary cross-sectional case-control study was carried out with 115 apparently healthy
Caucasian women. The POWIRS II (Profiles of Obese Women Suffering from the Insulin
Resistance Syndrome) study was performed in the Metabolic Unit of the North-West University,
Potchefstroom, South Africa. Here, dietary intake was measured using the quantitative food
frequency questionnaire (QFFQ). The ratio of energy intake (El) to basal metabolic rate (BMR) was
calculated from the reported El and BMR estimated using equations. Underreporters (URs) were
identified using the Goldberg equation, which compares El with energy expenditure (EE), both
expressed as multiples of the BMR. URs had reported El <1.27 x BMR, non-URs ≥1.27 x BMR.
Total energy expenditure (TEE) was calculated (n=115) and measured in a subgroup (n=63) by
using the Actical accelerometer. Physical activity was also divided into three groups by using the
Yale physical activity questionnaire.
Most of the women were overweight (45.8%) and 29.2% were obese but only 20 subjects
presented with the metabolic syndrome. The prevalence of underreporting women with a food
intake level (FIL; reported El divided by estimated BMR) below 1.27 was relatively low (21%).
Overreporting (FIL >2.4) was also low (6.7%). The prevalence of metabolic syndrome did not differ
between URs and non-URs (12.5% and 18.7%, respectively). Most subjects were younger than 35
years (mean=33.2), highly educated and received a high monthly income. The subjects fell mostly
into the low activity category. URs had a statistically significantly (p<0.05) higher percentage El
from fat but lower from carbohydrates (37.4% and 42.g0h, respectively) when compared to non-URs
(33.5% and 47%; respectively). The mean intakes of most micronutrients were statistically
significantly lower in the URs. However, expressed per energy unit, intakes of URs were
significantly higher for potassium, selenium and vitamin E. When the food group intakes of URs
and non-URs were compared no significant differences were found. Measured TEE was
significantly higher (p<0.01) in URs and non-URs (1 3 036kJ and 13 805kJ; respectively) compared
to calculated TEE (10 105.8kJ and 10 220.3kJ; respectively). Measured TEE was also significantly
higher than reported El (p<0.01). No specific subject characteristics were related to
underreporting. Considering the low reported El compared to the measured TEE, the cut off values
to identify URs might have been too low.
