George H. Beaton

Iron needs during pregnancy: do we need to rethink our targets?

This paper argues that current estimates of the need for absorbed iron, estimates of iron absorption, and hence estimates of iron requirements for pregnant women greatly depend on what is determined as the desirable or target hemoglobin concentration (goal). The existing goal appears to be based on the maximal hemoglobin concentration that can be achieved with iron supplementation of well-nourished women; this is a situation that can be expected to minimize iron absorption efficiency. I am unaware of attempts to define hemoglobin or anemia goals based on functional criteria (health of infant or mother). The current approach may seriously overestimate iron need and discourage food-based programs; furthermore, it may declare operational iron supplementation programs to be failures when, in fact, many programs may be successful in preventing functional effects of iron deficiency anemia. This is illustrated with data from a completed comparative study of daily and weekly iron supplementation. The final plea is to set aside existing traditions and, instead, attempt to develop functional criteria for anemia and establish functional goals of hemoglobin concentrations to be achieved during pregnancy.

Conceptual and methodological issues regarding the epidemiology of iron deficiency and their implications for studies of the functional consequences of iron deficiency.

This paper reviews the measures of iron status (hemoglobin, hematocrit, mean corpuscular hemoglobin concentration, mean cell volume, free erythrocyte protoporphyrin, serum iron, transferrin saturation, and serum ferritin) that are potentially available for inclusion in field studies of the relationship between iron and mental performance. The characteristics of these measures (sensitivity to iron status, specificity to iron, and diurnal and day-to-day variability) are reviewed and the implications of choice of variable for the design, analysis, and interpretation of studies are discussed. Brief consideration is given to the question of confounding variables and to sources of both false-positive and false-negative conclusions. The explicit message of the paper is that there is no perfect choice of measure of iron status but, given explicit definition of the research question, there are preferred choices that can most effectively combine the choice of variable and the design of the study.

ESTIMATING NUTRIENT DEFICIENCIES IN A POPULATION FROM DIETARY RECORDS: THE USE OF PROBABILITY ANALYSES

Abstract The objective of this report is to describe a probability approach, and to compare approaches, to evaluating dietary intake data. The nutrient intake data used were calculated from seven-day food records obtained from 83 Ontario teenagers and the adequacy of the estimated nutrient intakes was assessed by three approaches. First, mean nutrient intakes were compared to the recommended daily nutrient intakes (RDNI). Second, the proportion of the population not meeting the RDNI was calculated. Third, the distribution of nutrient intakes below the RDNI was determined, and combined with probability statistics to calculate the number of subjects likely to have intakes below their own individual requirements. This latter approach recognizes that the RDNI overestimates the nutrient requirement of almost all individuals in the population. The first approach was found to underestimate, whereas the second approach overestimated, possible problems. The third analysis appears to predict an incidence of nutrient inadequacy which is more in agreement with biochemical evidence. Therefore. given an adequate estimate of usual daily nutrient intakes of the individual, dietary data may be effectively used to identify nutrient problems in a population.

The Raymond Pearl memorial lecture, 1990: Nutrition research in human biology: Changing perspectives and interpretations

This paper addresses emerging concepts in the interpretation of anthropometric and dietary data. In the area of anthropometry, it argues the need for conceptualizations and constructs that recognize (1) the existence of a finite age range in which failing to grow is an active process followed by conversion to a state of having failed to grow; (2) the specific and nonspecific nature of anthropometric indices depending upon what is being marked; (3) the implication of secular trends in the interpretation of anthropometry; and (4) the need to move between consideration of individuals and populations. The implications of these for interpretation are illustrated. In the area of interpretation of dietary data, the main issues addressed relate to the conceptualization of needs of individuals and the aggregate needs of a population in the definition, description, and interpretation of “requirements.” In both areas, the core issue is the need for constructs that help address and interpret variability—variability of growth, variability of environmental constraints, variability of intake, and variability of needs and responses.

Urea formation in the pregnant rat.

Abstract Pregnant rats exhibit a smaller elevation of blood urea following the intraperitoneal injection of either alanine or casein hydrolyzate than do nonpregnant controls. This is interpreted as further evidence of a decrease in urea formation in pregnancy. The pregnant rats showed a greater and more prolonged elevation of blood urea following the administration of urea than did nonpregnant controls; this could explain the lack of a decrease in the fasting blood urea during gestation in the rat. Data obtained from pregnant rats after the surgical removal of the fetuses suggest that the low blood amino nitrogen during pregnancy is due to a withdrawal of amino acids into the fetal circulation.

Effect of anterior pituitary growth hormone on certain liver enzymes.

Summary In the adult male rat, an acute dosage of anterior pituitary growth hormone caused significant depressions in the rate of urea formation by liver slices, in liver arginase activity, and in liver alanine-glutamic transaminase activity but did not alter liver aspartic-glutamic transaminase activity. None of these effects were observed in young male rats, and in such animals, a significant elevation in liver alanine-glutamic transaminase activity was noted.

Nutritional Needs During the First Year of Life: Some Concepts and Perspectives

This article reviews some of the recent changes in thinking that are reflected in two reports (Recommended Nutrient Intakes for Canadians and the FAO/WHO/UNU Report on Energy and Protein Requirements) concerning nutrient requirements for infants below one year of age. The author illustrates the concepts underlying the published requirement estimates and hence some of the principles that should underlie the interpretation and application of the estimates.

Assessment of Vitamin B6 Nutriture in Pregnancy in the Rat.

Summary The response of several parameters of vit B6 nutriture (erythrocyte GPT and GOT, hepatic GPT and GOT, and xanthurenic acid excretion following a tryptophan load) to dosages of vit B6 ranging from 15 to 400 μg pyridoxine. HCl daily has been determined in pregnant and nonpregnant rats. All parameters except erythrocyte GPT appeared to be markedly affected by the state of pregnancy per se. Erythrocyte GPT was the most sensitive to the wide range of vit B6 doses employed. Erythrocyte GPT appears to be well suited for use as a parameter for the study of vit B6 requirements in pregnancy.

Fortification of Foods with Nutrients

Of all the foods consumed by man, none except human milk will give him complete nourishment, and then only during the first few months of life. In common with other animals, man is nourished by a variety of foods selected from the plants and animals present in his environment. While each of these foods usually contains small to large amounts of the 50 or more nutrients required for human nutrition, none can supply all these nutrients in correct proportions to meet the daily needs of human beings. The term fortification is used to describe the process by which nutrients are added to foods to maintain and improve the nutritional quality of diets (Table I). These nutrients may be added as concentrates, as extracts, or as synthetic compounds. The fortification of foods has often been described (1–4).

Perspectives and Priorities in Food and Nutrition Planning

I have taken this opportunity to challenge a trend that I have seen in recent meetings toward the promotion of a holistic, but perhaps impractical, approach to food and nutrition policy planning and implementation. While I support the development of modeling as an approach to the conceptualization of the problems and interactions, it would appear that the data requirements of the integrated nutrition policy approach exceed our present capabilities. I fear that this can result in inactivity at a time when we cannot afford inactivity--inactivity consequent to delay for data collection, or inactivity consequent to a belief that because comprehensive planning is not yet feasible, there is no point in doing any systematic planning. The precision of the definition of the nutrition problem is a function of the stage of development of the operational planning process. Let us not advocate the collection of data we are not equipped or prepared to interpret and use. In many areas of the world, relatively simple information, often already available, can define the nutrition problem with sufficient precision to permit program development within the individual sectors of government. Surely that must be our immediate goal.