A method to assess energy expenditure in children and adults.

More than 30 different methods have been used to assess physical activity. These methods can be grouped into seven major categories: calorimetry, job classification, survey procedures, physiological markers, behavioral observation, mechanical and electronic monitors, and dietary measures. No single instrument fulfills the criteria of being valid, reliable, and practical while not affecting behavior. The instruments that are very precise tend to be impractical on a population basis. Surveys are the most practical approach in large-scale studies, although little is known about their reliability and validity. Studies employing objective monitoring through heart rate, movement sensors, and doubly labeled water procedures appear promising, but are still experimental and costly. Despite the difficulty of measurement, relatively strong association has been found between physical activity and health, suggesting that, with improvements in assessment techniques, even stronger associations should be seen.

Assessment of physical activity in epidemiologic research: problems and prospects.

Under-reporting of food intake is one of the fundamental obstacles preventing the collection of accurate habitual dietary intake data. The prevalence of under-reporting in large nutritional surveys ranges from 18 to 54% of the whole sample, but can be as high as 70% in particular subgroups. This wide variation between studies is partly due to different criteria used to identify under-reporters and also to non-uniformity of under-reporting across populations. The most consistent differences found are between men and women and between groups differing in body mass index. Women are more likely to under-report than men, and under-reporting is more common among overweight and obese individuals. Other associated characteristics, for which there is less consistent evidence, include age, smoking habits, level of education, social class, physical activity and dietary restraint. Determining whether under-reporting is specific to macronutrients or food is problematic, as most methods identify only low energy intakes. Studies that have attempted to measure under-reporting specific to macronutrients express nutrients as percentage of energy and have tended to find carbohydrate under-reported and protein over-reported. However, care must be taken when interpreting these results, especially when data are expressed as percentages. A logical conclusion is that food items with a negative health image (e.g. cakes, sweets, confectionery) are more likely to be under-reported, whereas those with a positive health image are more likely to be over-reported (e.g. fruits and vegetables). This also suggests that dietary fat is likely to be under-reported. However, it is necessary to distinguish between under-reporting and genuine under-eating for the duration of data collection. The key to understanding this problem, but one that has been widely neglected, concerns the processes that cause people to under-report their food intakes. The little work that has been done has simply confirmed the complexity of this issue. The importance of obtaining accurate estimates of habitual dietary intakes so as to assess health correlates of food consumption can be contrasted with the poor quality of data collected. This phenomenon should be considered a priority research area. Moreover, misreporting is not simply a nutritionist's problem, but requires a multidisciplinary approach (including psychology, sociology and physiology) to advance the understanding of under-reporting in dietary intake studies.

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Assessing dietary intake : Who, what and why of under-reporting

▪Objectives:To determine whether relative vitamin D deficiency during the winter months contributes to age-related bone loss and whether rates of change in hard- and soft-tissue mass vary ...

Effect of Vitamin D Supplementation on Wintertime and Overall Bone Loss in Healthy Postmenopausal Women

Development of the doubly-labeled water method has made it possible to test the validity of dietary intake instruments for the measurement of energy intake. Comparisons of measured energy expenditure with energy intake from either weighed or estimated dietary records against energy expenditure have indicated that obese subjects, female endurance athletes, and adolescents underestimate habitual and actual energy intake. Individual underestimates of 50% are not uncommon. Even in non-obese adults, where bias is minimal, the standard deviation for individual errors in energy intake approaches 20%. Two investigations of the validity of self-reported dietary records for measuring change in dietary intake also indicate large underestimates of the actual change. Because of bias and imprecision, self-reported energy intakes should be interpreted with caution unless independent methods of assessing their validity are included in the experimental design.

M J Stock

Papers

The measurement of food and energy intake in man-an evaluation of some techniques.

The measurement of daily energy expenditure--an evaluation of some techniques.

A longitudinal study of body weight and body fat changes in Antarctica.