Janet C. King

Physiology of pregnancy and nutrient metabolism

Pregnancy consists of a series of small, continuous physiologic adjustments that affect the metabolism of all nutrients. The adjustments undoubtedly vary widely from woman to woman depending on her prepregnancy nutrition, genetic determinants of fetal size, and maternal lifestyle behavior. Studies of protein and energy metabolism illustrate the potential of adjusting the use of those nutrients to conserve a fetal supply. Adjustments in the metabolism of nitrogenous compounds are in place by the second quarter of pregnancy. During the last quarter of pregnancy, when fetal demands are greatest, those adjustments allow a positive nitrogen retention. The energy requirement of basal metabolism is influenced by maternal prepregnant nutrition and by fetal size. If maternal energy reserves are low at conception, the basal metabolic rate is down-regulated to conserve energy. Also, women having larger babies tend to have greater increases in their basal metabolic rate and lower rates of maternal energy storage. Changes in maternal food and physical activity behaviors during gestation may augment the physiologic adjustments. However, the substantial variability in food intakes and physical activity makes it difficult to show those changes. Thresholds in the capacity to adjust nutrient use to the amount supplied exist for all nutrients. When intakes fall below the threshold, fetal growth and development is affected more than is maternal health. Efforts to achieve good maternal nutritional status preconception as well as throughout gestation best assure a good milieu for fetal growth and development.

Energy requirements during pregnancy and lactation

OBJECTIVE To estimate the energy requirements of pregnant and lactating women consistent with optimal pregnancy outcome and adequate milk production. DESIGN Total energy cost of pregnancy was estimated using the factorial approach from pregnancy-induced increments in basal metabolic rate measured by respiratory calorimetry or from increments in total energy expenditure measured by the doubly labelled water method, plus energy deposition attributed to protein and fat accretion during pregnancy. SETTING Database on changes in basal metabolic rate and total energy expenditure during pregnancy, and increments in protein based on measurements of total body potassium, and fat derived from multi-compartment body composition models was compiled. Energy requirements during lactation were derived from rates of milk production, energy density of human milk, and energy mobilisation from tissues. SUBJECTS Healthy pregnant and lactating women. RESULTS The estimated total cost of pregnancy for women with a mean gestational weight gain of 12.0 kg, was 321 or 325 MJ, distributed as 375, 1200, 1950 kJ day(-1), for the first, second and third trimesters, respectively. For exclusive breastfeeding, the energy cost of lactation was 2.62 MJ day(-1) based on a mean milk production of 749 g day(-1), energy density of milk of 2.8 kJ g(-1), and energetic efficiency of 0.80. In well-nourished women, this may be subsidised by energy mobilisation from tissues on the order of 0.72 MJ day(-1), resulting in a net increment of 1.9 MJ day(-1) over non-pregnant, non-lactating energy requirements. CONCLUSIONS Recommendations for energy intake of pregnant and lactating women should be updated based on recently available data.

Popular Diets: Correlation to Health, Nutrition, and Obesity

OBJECTIVE To examine the association between a range of health and nutrition indicators and popular diets. DESIGN The Continuing Survey of Food Intake by Individuals (CSFII) 1994-1996 data were used to examine the relationship between prototype popular diets and diet quality as measured by the healthy eating index (HEI), consumption patterns, and body mass index (BMI). The prototype diets included vegetarian (no meat, poultry, or fish on day of survey) and non-vegetarian. The nonvegetarian group was further subdivided into low carbohydrate (less than 30% of energy from carbohydrate), medium (30% to 55%), and high (greater than 55% of energy). Within the high carbohydrate group, participants were classified as having Pyramid or non-Pyramid eating patterns. The Pyramid group was defined as 30% or less of energy from fat and at least one serving from the five major food groups in the USDA Food Guide Pyramid. Finally, the non-Pyramid group was further subdivided into low fat (less than 15% of energy from fat) and moderate fat (15% to 30% of energy from fat). In addition, a review of the published scientific literature was conducted; all studies identified were included in the review. SUBJECTS 10,014 adults, aged 19 years and older, from the 1994-1996 CSFII were included in the analyses of extant data. More than 200 individual studies were included in the review of the literature. RESULTS Analyses of the CSFII indicate that diet quality as measured by HEI was highest for the high carbohydrate Pyramid group (82.9) and lowest for the low carbohydrate group (44.6). Energy intakes were low for the vegetarians (1,606 kcals) and high carbohydrate/low fat group (1360 kcals). BMIs were lowest for women in the vegetarian group (24.6) and the high carbohydrate/low fat group (24.4); for men, the lowest BMIs were observed for vegetarians (25.2) and the high carbohydrate Pyramid group (25.2). Review of the literature suggests that weight loss is independent of diet composition. Energy restriction is the key variable associated with weight reduction in the short term. CONCLUSIONS Diets that are high in carbohydrate and low to moderate in fat tend to be lower in energy. The lowest energy intakes were observed for those on a vegetarian diet. The diet quality as measured by HEI was highest for the high carbohydrate groups and lowest for the low carbohydrate groups. The BMIs were significantly lower for men and women on the high carbohydrate diet; the highest BMIs were noted for those on a low carbohydrate diet.

Use of Serum Zinc Concentration as an Indicator of Population Zinc Status

Assessing the prevalence and severity of zinc deficiency in populations is critical to determine the need for and appropriate targeting of zinc intervention programs and to assess their effectiveness for improving the health and well-being of high-risk populations. However, there is very little information on the zinc status of populations worldwide due to the lack of consensus on appropriate biochemical indicators of zinc status. The objective of this review was to evaluate the use of serum zinc concentration as an indicator of population zinc status. We have reviewed the response of serum zinc concentration to dietary zinc restriction and zinc supplementation. In addition, we completed pooled analyses of nine zinc intervention trials in young children to assess the relations between serum zinc concentration of individuals before treatment and their responses to zinc supplementation. Also, in updated combined analyses of previously published data, we investigated the relation between the mean initial serum zinc concentration of a study population and their mean growth responses to zinc supplementation in randomized intervention trials among children. The results from depletion/repletion studies indicate that serum zinc concentrations respond appreciably to severe dietary zinc restriction, although there is considerable interindividual variation in these responses. There is also clear evidence that both individual and population mean serum zinc concentrations increase consistently during zinc supplementation, regardless of the initial level of serum zinc concentration. By contrast, an individuals serum zinc concentration does not reliably predict that persons response to zinc supplementation. Serum zinc concentration can be considered a useful biomarker of a populations risk of zinc deficiency and response to zinc interventions, although it may not be a reliable indicator of individual zinc status.

Effects of nandrolone decanoate therapy in borderline hypogonadal men with HIV-associated weight loss.

Serum testosterone concentrations are frequently in the low-normal range (lowest quartile, <500 ng/dl) in men with AIDS-wasting syndrome (AWS) and in other chronic wasting disorders. The response of patients in this group to androgen treatment has not been determined, however. Eighteen men with AWS (mean +/- standard error [SE]: 87% +/- 1% usual body weight; CD4 count 90 +/- 24) and borderline low serum testosterone concentrations (382 +/- 33 ng/dl) completed a 21-day placebo-controlled inpatient metabolic ward study comparing intramuscular (i.m.) placebo (n = 7) with low-dose (65 mg/week; n = 4) and high-dose (200 mg/week; n = 7) nandrolone decanoate, a testosterone analogue. Nitrogen balance, stable isotope-mass spectrometric measurement of de novo lipogenesis (DNL), resting energy expenditure, and gonadal hormone levels were measured. Both low-dose and high-dose nandrolone resulted in significant nitrogen retention (33-52 g nitrogen/14 days, representing gains of 0.5 to 0.9 kg lean tissue/week) compared with placebo (loss of 11 g nitrogen/week). This was reflected biochemically in a borderline significant reduction of high DNL (p < .06). Serum testosterone and gonadotropins were suppressed whereas resting energy expenditure was unchanged by nandrolone treatment. In 10 study subjects completing a 12-week open-label follow-up phase, body weight increased by 4.9 +/- 1.2 kg, including 3.1 +/- 0.5 kg lean body mass, and treadmill exercise performance also improved. In summary, nandrolone decanoate therapy in the absence of an exercise program in borderline hypogonadal men with AWS caused substantial nitrogen retention compared with placebo, similar in extent to the nitrogen retention previously achieved with recombinant growth hormone. It is reasonable to expand the criteria for androgen treatment in AWS to include at least patients in the lowest quartile of serum testosterone.

Effects of maternal zinc supplementation on pregnancy and lactation outcomes.

Observational studies in human populations suggest that maternal zinc deficiency during pregnancy may cause adverse pregnancy outcomes for the mother and fetus. Therefore, we reviewed the current evidence from studies of zinc supplementation, with or without other micronutrients, during pregnancy and lactation to assess its impact on maternal, fetal, and infant health. A meta-analysis of supplementation trials indicates a 14% reduction in premature delivery among zinc-supplemented women. Most studies found no significant impact of maternal zinc supplementation on infant birthweight, but a subset of studies conducted in underweight or zinc-deficient women suggests that there may be a positive effect of zinc supplementation in such women. However, the number of relevant studies is limited, and more information is needed to confirm these observations. The results for other pregnancy outcomes are inconsistent, and the number of available studies is small. Likewise, the impact of maternal zinc supplementation during pregnancy on infant postnatal growth and risk of infection is variable, and few studies are available. Thus, more research will be needed to allow definitive conclusions to be drawn, especially for the second half of infancy and later childhood. Studies found no adverse effects of maternal zinc supplementation on iron status during pregnancy. More information is required on other potential adverse effects, particularly with regard to a possible modifying effect of preexisting maternal zinc status. In view of the possible benefits of zinc supplementation for reducing the risk of premature delivery, the possible positive impact of zinc supplementation on infant birthweight among undernourished women, and the lack of reported adverse effects, zinc should be included in maternal supplements given during pregnancy in populations at risk for zinc deficiency.

Nutrient regulation during pregnancy, lactation, and infant growth

Almost every aspect of energy and nutrient metabolism is altered by hormonal and other physiological changes during pregnancy and lactation. While it is evident that hormonal adjustments affect nutrient requirements, these are rarely considered when nutrient recommen- dations are made for pregnant or lactating women, and often neglected during evaluation of nutritional status. In addition, changes in nutrient metabolism during the stages of pregnancy and oflactation are usually considered separately, while in reality events during pregnancy can have a major influence on nutritional status and nutrient requirements during lactation. The purpose of this volume is to describe changes in the metabolism of important nutrients during pregnancy and lactation, including the physiological basis for these changes and their implications for nutrient requirements and assessment. Authors have considered such issues as inter-relationships between endocrine changes and nutrient metabolism at the tissue, cellular and molecular level; alterations in nutrient binding proteins; the efficiency of nutrient absorp- tion and retention; and the impact on maternal as well as fetal nutritional status. Another unique aspect of this book is the focus on pregnancy and lactation as a continuum.

Zinc homeostasis in pediatric critical illness.

Objective: We explored the hypothesis that marked decline in plasma zinc concentrations among critically ill children is related to shifts in metallothionein expression and inflammation. Design: Prospective pilot study. Setting: Intensive care unit of tertiary care children’s hospital. Patients: All children (<18 yrs) with unadjusted Pediatric Risk of Mortality III score >5 or at least one organ failure admitted to the pediatric intensive care unit from March through August 2006 were eligible for enrollment. Interventions: After consent, blood samples were collected on days 1 and 3 of illness and analyzed for serum chemistries, plasma zinc and copper levels, metallothionein isoform expression, and cytokine levels. Measurements and Main Results: Twenty patients were enrolled, with median age of 2.9 yrs (interquartile range, 0.7–10.1). Male to female ratio was 1.2:1. All patients had low zinc levels (mean, 0.43; range, 0.26–0.66 &mgr;g/dL) on day 1 of pediatric intensive care unit admission, and remained low (mean, 0.51; range, 0.26–0.81 &mgr;g/dL) on day 3, even when corrected for hypoalbuminemia. In comparison, serum copper levels were normal. On day 1, there was a positive correlation between zinc levels and expression of MT-1A (p < 0.01), MT-1G (p = 0.02), and MT-1H (p = 0.03). Plasma zinc levels correlated inversely with C-reactive protein levels (r = −.75, p = 0.01) and interleukin-6 levels (r = −.53, p = 0.04) on day 3. On day 3, patients with two or more organ failures had significantly lower plasma zinc concentrations compared with patients with ≤1 organ failure (p = 0.03). Conclusions: Plasma zinc concentrations are low in critically ill children. Plasma zinc correlated with measures of inflammation (C-reactive protein and interleukin-6) on day 3; low plasma zinc concentrations were associated with the degree of organ failure on day 3. These data serve as the basis for a larger study of shifts in plasma zinc concentrations in critically children to potentially identify patients who might benefit from zinc supplementation.

Nutritional Concerns During Adolescence

Adolescent food habits often run counter to the special nutritional needs of this age group. Suggestions for nutrient supplements are offered, with particular emphasis on fulfilling the unique needs of the obese, athletic, or pregnant teenager.

Efficacy of a group‐based dietary intervention for limiting gestational weight gain among obese women: A randomized trial

Observational studies suggest that minimal gestational weight gain (GWG) may optimize pregnancy outcomes for obese women. This trial tested the efficacy of a group‐based weight management intervention for limiting GWG among obese women.