The popular use of epidemiology in nutrition requires that the tools used are accurate. If conclusions are drawn for associations between dietary intake and other variables the whole study is flawed when the results are incorrect.
Estimating under-reporting of energy intake in dietary surveys using an individualised method
Rennie et al British Journal of Nutrition , 2007, 97, 1169-76
This study compares a method of estimating under reporting using individualised estimates of energy requirements, against the Goldberg cut-off method in measuring under reporting of energy intake in the 2000 National Diet and Nutrition Survey and against doubly labelled water measures of Total Energy Expenditure in the National Diet and Nutrition Survey feasibility study.
Assessments of diet in epidemiological studies are usually based on self-report methods but the validity of these methods is dependent on the accuracy with which participants record their dietary intake. The Under-reporting of energy intake by self-reported dietary methods is well recognised. The methods used to estimate under reporting in population-based studies commonly assume a sedentary lifestyle.
This study in a population aged 19-64 years compares estimated under reporting using individualised estimates of energy requirements with a population cut-off based on minimum energy needs. Physical activity diaries and 7d weighed dietary records were completed concurrently. Mean daily energy intake was calculated from the dietary records.
Reported physical activity was used to define each subject’s activity level, and then to calculate estimated energy requirements from published equations. The doubly-label led water) method provides an accurate measure of total energy expenditure
Most commonly, reported dietary intake is expressed as a multiple of BMR estimated from equations and a cut-off applied, below which subjects arc identified as low-energy reporters (Goldberg et al . This is usually applied to individuals, and the Goldberg cut-off technique was devised primarily to define under reporting under reporting in groups level. It is excellent for under reporting in sedentary subjects, but less useful in subjects with higher energy expenditures. This method introduces systematic bias in a mixed population
By the individual method under reporting was approximately 27 % of energy needs in men and 29% in women, with 75% of men and 77% of women classified as under-reporters. Using the population method 80 and 88% were classified as under-reporters respectively. When subjects who reported their eating being affected by dieting or illness during dietary recording were excluded, under reporting was 25 % of energy needs in both sexes. As one would expect under reporting was higher in overweight and obese men and women compared with their lean counterparts Under reporting of energy intake must be considered in dietary surveys.
- Martin Eastwood