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  • Title: Estimating energy and nutrient intakes in studies of human fertility.
    Author: Ulijaszek SJ.
    Journal: J Biosoc Sci; 1992 Jul; 24(3):335-45. PubMed ID: 1634562.
    Abstract:
    Two methods of dietary recording, the 24-hr recall and the weighed dietary intake methods, are considered appropriate for estimating energy and nutrient intakes in studies of human fertility. The former method gives lower estimates than the latter, although weighed intakes may underestimate true intakes. Examination of food intakes of pregnant, lactating, and non-pregnant, non-lactating New Guinean women shows their diet to be less homogeneous than is generally assumed for groups in developing countries. As a result direct observations of food intake for a limited number of days are not sufficiently accurate for the estimation of intake of most of the nutrients examined. Rather the study design should reflect the variability of intakes of the nutrients and groups under consideration. A group of Ningerum women in Hukim, Papua New Guinea, were observed in order to examine the within-subject and between-subject food intake variance in energy and nutrients. Women were grouped as late pregnant, early lactating, and early pregnant, late lactating, and nonpregnant, nonlactating women. The 2 most common measures of dietary intake are the 24-hour recall and weighed dietary intake. 24-hour recall is appropriate for large sample sizes and must adequately represent all days of the week. Weighed dietary intake is a more accurate tool, but observers may influence the reporting of habitual patterns. Both methods require a specified time frame. Energy and nutrient intake measures are important as proxies for total daily energy expenditure (TEE), which is more difficult to determine. Chronic energy deficiency is an important health factor in pregnant or lactating women in suppressing human reproductive function. Diets tend to be similar between pregnant and nonpregnant women. A brief review of the methods and accuracy of methods of assessing energy and nutrient intakes is presented. There is evidence that dietary recall is always lower than weighed intake, in some cases by 19% and in a few cases by as much as 70%. Standards have been established for estimating baseline energy needs for survival, active, and inactive adults. These standards may not be very accurate at extremes of body weight. The rank of absolute energy intake within groups is not without its accuracy problems also. There are no studies available on nutrient intakes of women in developing countries; the assumption is that dietary intakes are homogeneous from day to day. This study used 5-day weighed dietary intakes on 37 adult females between 18-40 years in May 1984. Food composition tables were from several sources. Water content was estimated from samples of different foods. All were weighed and the basal metabolic rate (BMR) determined. An intake to BMR ratio was calculated and found similar in all 3 groups, between 1.61 and 1.65. The methods of Black et al. and Nelson et al. were used in determining the number of days of diet record for correctly classifying 80% of subjects. The number of days varies between nutrients and physiological state. The result was that a limited number of days does not accurately estimate intake of the nutrients examined. A pilot study design is needed that reflects the variability of intakes of nutrients and groups under consideration, including the possible seasonality of eating patterns.
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