Do we eat less fat, or just report so?

OBJECTIVE: To examine secular trends in diet reporting error.
METHODS: Dietary information was obtained from 228 Danish men and women in 1987-88, and from 122 men and women in 1993-94.
RESULTS: Bias in dietary reporting of energy and protein intake was assessed by comparing reported intake with intake data, estimated from 24 h nitrogen output, validated by administering P-aminobenzoic acid, and estimated 24 h energy expenditure. Total energy was under-reported more than energy from protein at both surveys, suggesting that energy from other nutrients, like fat and/or carbohydrate, must have been under-reported too. There was a greater under-reporting for energy than for protein in 1993-94 (29%) than in 1987-88 (15%). Obesity was positively associated with under-reporting, both in 1987-88 and in 1993-94.
CONCLUSION: The higher macro-nutrient specific error in 1993-94 compared to 1987-88 may reflect a trend to increasingly omitting fat and/or carbohydrate-rich foods in dietary reporting. This may be a consequence of increased awareness of diet intake, which, in turn, may be related to intensified public health campaigns to reduce intake of fat and/or simple carbohydrate. These results may have consequences for our understanding of the apparent decline in dietary fat and associated health benefits.