Body composition and energy intake: do overweight women overeat and underreport?

The relationship between energy consumption and body composition was evaluated in 63 women by use of energy-intake values that were precisely measured in a metabolic unit and corrected for deviations from energy balance. Energy requirement for the maintenance of body weight was not significantly correlated with adiposity expressed as percent body fat. However, energy requirement was positively associated with lean mass (p less than 0.0001) whereas fat mass added no predictive value to the same multivariate regression equation. Self-reported energy intake (before the experiments) was not correlated with lean mass and was underestimated by lean subjects at least as much as by obese subjects. Discrepant findings in the literature concerning relationships between obesity and energy intake may be explained by reporting error and by the relative lean mass of obese vs nonobese women but not by systematic underreporting unique to obese subjects.

Accuracy of heart-rate monitoring and activity diaries for estimating energy expenditure

The accuracy of heart-rate monitoring and activity diaries for measuring energy expenditure in free-living individuals was studied in 12 women. Estimates of energy expenditure were calculated from heart-rate monitoring by use of four different prediction equations to describe the relationship between heart rate and energy expenditure. Estimates of energy expenditure from activity diaries were calculated using both individually measured and published values for the energy cost of activities. Energy intake adjusted for changes in body-energy stores was used as a reference. Heart-rate monitoring overestimated group energy expenditure from 2 to 9% and the errors in estimating individual energy expenditure ranged from -53 to 67%. Activity diaries underestimated group energy expenditure by 2-6% and the errors in estimating individual energy expenditure ranged from -39 to 56%. Heart-rate monitoring and activity diaries may prove useful for estimating the energy expenditure of groups but not individuals.

Iron deficiency anemia and steady-state work performance at high altitude

Thirty-seven young adult male highland residents at 3,600-4,100 m in La Paz, Bolivia, performed short-duration cycle ergometry at 60, 80, and 100% of maximal voluntary O2 consumption (VO2max). Three groups of subjects representing the high-altitude population mean hemoglobin (Hb), the 10th percentile Hb, and below the 1st percentile were examined to test the hypothesis that the relationship of exercise performance to Hb concentration is similar to those relationships established at low altitude. Anemic individuals (n = 8) had 23% lower voluntary VO2max and 28% lower maximal work loads compared with controls (n = 17) or marginally anemic subjects (n = 12) although the relationship of VO2 to work load was similar. Anemic individuals maintained significantly higher arterial O2 partial pressures and Hb saturations during heavy exercise (90 +/- 0.5 vs. 85 +/- 0.6%) in conjunction with a greater heart rate up to maximal effort. A significantly decreased erythrocyte 2,3-diphosphoglycerate (2,3-DPG)-to-Hb molar ratio (0.70 +/- 0.04 vs. 1.12 +/- 0.06), suggestive of a left-shifted dissociation curve in anemics, is in contrast to the expected right-shifted curve. Moderate anemics were similar to controls. Anemic individuals did not differ in arterial lactate concentration from controls at absolute work loads; anemics had significantly lower arterial lactate concentrations at maximal effort than controls with no differences in the work load-to-lactate relationship. In conclusion, O2 transport during exercise at high altitude seems unaffected by the Hb concentrations as low as the 10th percentile of the population mean.(ABSTRACT TRUNCATED AT 250 WORDS)

On the factors which contribute to thinning of the villous membrane in human placentae at high altitude. II. An increase in the degree of peripheralization of fetal capillaries

The contribution made by fetal capillary peripheralization to the thinning of the villous membrane seen in human placentae from high-altitude pregnancies is examined by stereological methods. Variables characterizing the shape of the villous core and the spatial relationships between trophoblast and capillaries are quantified. They shed light on the relative importance of dynamic versus mechanistic processes of villous membrane attenuation. Highland villi differ from lowland villi in several ways. On average, they possess a thinner barrier due to closer approximation of capillaries to overlying trophoblast; in consequence, the villous core is more irregular in outline and its surface (that of the inner aspect of the trophoblast) exceeds in area that of the outer aspect of the trophoblast. These results suggest that the dynamic process (protoplasmic streaming within syncytiotrophoblast) cannot alone explain thinning of the villous membrane. A mechanistic process (capillary peripheralization and obtrusion into the trophoblastic epithelium) is sufficient to account for the differences observed, although the possibility that both processes operate concurrently cannot be discounted. This report completes a study into factors contributing to villous membrane thinning at high altitude.

On the factors which contribute to thinning of the villous membrane in human placentae at high altitude. I. Thinning and regional variation in thickness of trophoblast

Sections of human term placentae delivered at low and high altitude to indigenous and non-indigenous populations in Bolivia were analysed by stereological methods. Estimates were obtained of the arithmetic and harmonic mean thicknesses of villous membrane and of trophoblast. These values were then used to derive indices of thickness variation. No significant ethnic, sex or interaction effects were found. At high altitude, the villous membrane was significantly more variable in thickness owing to a lower harmonic mean but the same arithmetic mean thickness. Alterations in the arithmetic and harmonic mean thicknesses of the trophoblast contributed to the thinning of the villous membrane. The trophoblast was thinner and more irregular in thickness at high altitude. These findings are discussed in the context of placental diffusing capacity and the possible mechanisms for formation of vasculosyncytial membranes.

Morphometric studies on villi in human term placentae and the effects of altitude, ethnic grouping and sex of newborn

Stereological methods were used to test whether or not altitudinal, ethnic and sex differences in birthweight in Bolivia are associated with differences in placental morphology. Estimates of the volumes, surface areas, lengths and diameters of villi and of fetal capillaries were obtained by analysing paraffin sections of tissue. The average highland placenta contains villi of smaller overall volume, surface area and length. These villi possess a less voluminous fetal vascular space, and the capillaries are smaller in mean diameter. The average Amerindian placenta has longer but thinner capillaries than the average placenta delivered by non-indigenous women. Altitude and ethnic grouping interact to have an effect on total villous length, whilst ethnic grouping and sex interact to influence fetal capillary length. These structural differences are discussed in the context of their likely impact on placental functioning, notably on exchange by passive diffusion.

Variation in early neonatal mortality for different types of fetal growth retardation

Birth and first-48-hr death records were analyzed for 10,024 liveborn infants in Mexico City and 12,786 liveborn infants in Santa Cruz, Bolivia. The objective of the analysis was to characterize the early postnatal mortality rates for different types of fetal growth retardation and prematurity. Infants who were delivered prior to 37 weeks of gestation had 23-100 times the mortality risk of infants born at full term and normal weight. Light-for-gestational-age infants (birth weight less than 2,900 g) were further divided into proportionately growth-retarded with normal Rohrer's index (weight/height) and disproportionately growth-retarded with low Rohrer's index. The proportionately growth-retarded infant had nearly twice the mortality of the full-term, appropriate-weight infants, whereas the disproportionately growth-retarded infants had 2.9-5.7 times the mortality rate of the full-term, appropriate-weight infants. There were some differences between samples in mortality rates and prevalence of the different classes of small infants, but the pattern of mortality within samples was consistent between samples.

The volumetric composition of human term placentae: altitudinal, ethnic and sex differences in Bolivia

Point counting volumetry has been used to decide whether or not altitudinal, ethnic and sex differences in birth weight in Bolivia are accompanied by changes in placental composition. Sixty eight placentae from healthy, term pregnancies were sampled from populations of Amerindian and non-Indian women living in Santa Cruz (400 m) and La Paz (3600 m). Altitudinal reductions in birth weight were not accompanied by significant alterations in placental weight yet highland placentae were substantially different in histological composition. On average, the highland placenta had a more voluminous intervillous space but reduced volumes of villi, juxtavillous fibrin and non-parenchyma. Whilst Amerindian newborn were heavier, placental weights were similar in both ethnic groups. However, the Amerindian placenta tended to possess more trophoblast and more villous stroma than its non-Indian counterpart. No sex differences were detected save for an interaction effect on fibrin which involved altitude, ethnic group and sex. Findings are discussed in the context of known morphometric and physiological differences between placentae in different experimental groups, notably in other types of pregnancy associated with reduced fetal growth.

Functional anemia of complicated protein-energy malnutrition at high altitude

The effect of severe protein-energy malnutrition (PEM) on erythropoiesis in children living in the highlands of Bolivia, altitude 3700 m, was studied. Forty percent reduced hemoglobin concentrations, significantly lower arterial oxygen tensions, and a right-shifted, oxygen-dissociation curve were observed compared to high-altitude controls. Serum and erythrocyte folate concentrations were 44% and 82%, respectively, of control values. Low initial transferrin saturation decreased significantly during the 10-wk refeeding period. Thus, iron and folate deficiency contributed significantly to the poor red cell response. Results suggest that the anemia associated with severe PEM has a more significant impact on oxygen transport at high altitude than at sea level and requires an adaptive response in the oxygen-dissociation curve to satisfy tissue-oxygen demands. Furthermore, marginal iron and folate status and an inflammatory block of iron supply may limit the reestablishment of a normal tissue mass during refeeding.

Hematologic evidence of fetal hypoxia among newborn infants at high altitude in Bolivia

The reduced birth weight widely reported for high-altitude infants has been attributed to intrauterine hypoxia. This assertion may be tested by comparing hematologic values of high-altitude and low-altitude newborn infants, since the human fetus can respond to intrauterine hypoxia with enhanced erythropoiesis. This report presents cord blood values of term Bolivian infants classified by altitude, ethnic group, and parity: 105 from La Paz (3600 m) and 46 from Santa Cruz (400 m). Hematocrit, hemoglobin concentration, and the proportion of hemoglobin F are higher among newborn infants at high altitude. Ethnic group and parity interact with altitude in effect on hematocrit and hemoglobin concentration. Gestational age, birth weight, maternal hematologic variables, and socioeconomic indicators are not significantly associated with cord blood values. The high-altitude newborn infant displays evidence of enhanced erythropoiesis, which supports the suggestion that the high-altitude fetus experiences a greater degree of hypoxia in utero than does the low-altitude fetus.

Combined effects of exercise and restriction of energy intake on moderately obese women

The current study was designed to assess the contribution of dietary-induced weight reduction on improvements in functional capacity in moderate obesity. Twelve females (means age = 29 yr, means fat percentage = 37%) served as subjects for the study. Subjects trained on a cycle ergometer 30 min.day-1, six day.wk-1 for three or six weeks at 75 to 85 per cent of maximum heart rate (HR max). Improvements in maximal oxygen uptake (delta VO2 max I.min-1) and functional capacity (delta VO2 max ml.kg-1 min-1) were compared in an attempt to separate out training and dietary effects respectively. Measurements were also taken on both the cycle ergometer and treadmill to test for any specificity of training effects. Changes in body composition were assessed by densitometry. Following three weeks of training, there was an average increase in VO2 max ml.kg-1 min-1 on the cycle ergometer and the treadmill of 14 and 19 per cent respectively. By six weeks, this had increased to 18 and 26 per cent respectively. The contribution of weight reduction to the improvements in functional capacity was calculated to range from 20 to 33 per cent. Thus, both energy restriction and exercise training appear to be effective means of improving functional capacity in moderately obese women.

The effects of exposure misclassification on estimates of relative risk

In epidemiologic studies, individuals may be misclassified with respect to exposure to a risk factor for disease. Such misclassification causes the relative risk of disease associated with the exposure in the population to be biased toward the null value. Here, a formula is derived for the apparent relative risk under misclassification (R) as a function of the sensitivity (U) and specificity (V) of the test for exposure and of the true relative risk (R) and true prevalence of exposure (P(E] in the population. The relative influence of U and V on the bias in R depends both on R and on P(E), with U tending to be more influential at higher values of P(E). When there is misclassification of exposure, variation in P(E) may bias comparisons of relative risk between groups or exposures, either by producing spurious differences or by masking true differences, and may generate spurious trends associated with a third variable such as age. Because the possible effects of misclassification of exposure on relative risk are complex and not easily generalized, the potential degree of bias should be evaluated individually in each situation.

Microscopical morphology of the human placenta and its effects on oxygen diffusion: a morphometric model

A combination of stereological and physicochemical data was used to estimate the oxygen-diffusing capacity of the human term placenta. The effects on this morphometric diffusing capacity of isolated changes in placental structure were investigated by permitting volumes, surface areas and harmonic mean diffusion distances to deviate from normal baseline (term) values. Diffusion performance could be monitored effectively by estimating only three structural quantities. The most influential variable was the harmonic mean thickness of the villous membrane followed by the surface areas of villi and of fetal capillaries. Blood space volumes and plasma diffusion distances had negligible effects on diffusing capacity. Conclusions are discussed in the context of published findings on changes in placental anatomy which occur during gestation, abnormal pregnancies and pregnancies at high altitude.

Distribution of hemoglobin and functional consequences of anemia in adult males at high altitude

In order to assess better the normal hemoglobin (Hb) range among adult males at high altitude, a hematological survey was completed in La Paz, Bolivia (3700 m). Two statistical methodologies were utilized to identify the anemic and polycythemic contributions to the Hb distribution of normal healthy men (n = 526). The Hb of normal men has a Gaussian distribution with mean and SD of 18.8 +/- 1.4 g/dl. Cutoff levels of 15.8 and 22.0 g/dl Hb were selected to identify the anemic and polycythemic subpopulations. Iron status in this high altitude population is similar to that of low altitude populations, and iron deficiency is the cause of most anemia found. An exercise test on a subsample of 56 men was utilized to validate the anemia cutoff level. Anemics as identified by the 15.8 g/dl Hb level showed a significant reduction in aerobic capacity as measured by PWC150 and estimated VO2max.

Stereological studies on the true thickness of the villous membrane in human term placentae: a study of placentae from high-altitude pregnancies

Stereological principles were used to calculate functionally significant dimensions of the human villous membrane, its arithmetic mean thickness (Ta) and its harmonic mean thickness (Th). The former is proportional to tissue mass and oxygen consumption, the latter to diffusional resistance. For a group of 15 term placentae from uncomplicated pregnancies at high altitude, the average values were Ta = 4.44 micron, Th = 3.56 micron and Ta/Th = 1.26. The latter figure provides a useful quantitative expression for the efficiency of the membrane in gas and metabolite diffusion. It implies that vasculosyncytial membranes and syncytial knots decrease resistance to diffusion by 26 per cent, compared with that of a membrane with uniform thickness throughout. The methods are simple to apply and provide better estimates of true thickness than do measurements confined to thin sections.

Structure-function correlation in the human placenta: the morphometric diffusing capacity for oxygen at full term

A combination of stereology and physiology is used to estimate the morphometric diffusing capacity for oxygen of the normal human placenta at term. The morphometric diffusing capacity is found to be higher than published values determined by physiological methods. The most likely explanation for this discrepancy is that physiological values are too low because of the effects of shunts, placental oxygen consumption and uneven diffusion:perfusion ratios. Despite the discrepancy, morphometry of histological sections offers a valuable and practicable alternative for comparing the functional potential of the placenta in different species, during normal gestation, disease, experimental treatment and environmental hypoxic stress.

Work performance of high-altitude Aymara males

The sample for this study consisted of 28 Aymara males between the ages of 15 and 43 years. The subjects were rural high-altitude natives who were temporarily working as porters in La Paz, Bolivia (3700 m). Mean VO2max was 46 X 5 ml/kg/min. There was a significant negative relationship between VO2max and age in adult porters . However, there was also a significant positive relationship between maximal work output and age and a significant negative relationship between VO2 during submaximal exercise and age. Relative work intensity (VO2/VO2max) during submaximal exercise did not change significantly with age. Thus, even though VO2max decreased significantly with age, these data suggest that there may not be a substantial decrease with age in the adaptive status of these men. Minimal support was found for the hypothesis that chest size in Andean highlanders influences the effectiveness of the oxygen transport system.

Anthropometric survey of high-altitude Bolivian porters

This paper presents the results of an anthropometric survey of 138 rural Aymaran high-altitude males who were working as porters in La Paz, Bolivia (3700 m). All subjects were measured for stature, weight, upper arm circumference, and triceps skinfolds. The body size and composition of the porters were then compared to an Aymaran rural population from the Bolivian highlands, and urban mestizo labourers from La Paz. The porters were smaller than the urban sample, but appeared to be generally representative of rural Aymaran natives with respect to body size and composition, and nutritional status. It is suggested that towards one extreme of nutritional variability, some degree of undernutrition may be indicated, which should be considered in future studies of adaptation to hypoxia among these Andean highlanders.

Effects of exercise on riboflavin requirements of young women

The riboflavin requirement of young women during periods of sedentary living and exercise was determined during a 12-wk metabolic study. The study was divided into a 6-wk no exercise period followed by a 6-wk exercise period in which subjects jogged around a track for 20 to 50 min/day. Twelve subjects, aged 19 to 27 yr, were fed a basic diet containing 0.6 mg riboflavin/1000 kcal of intake. Riboflavin intake was increased by 0.2 mg/1000 kcal increments by provision of riboflavin in a glucose polymer mixture. Linear regression analysis was used to estimate the riboflavin intake required for an erythrocyte glutathione reductase activity coefficient of 1.25 during both the no exercise and exercise periods. Individual riboflavin requirements ranged from 0.62 to 1.21 mg/1000 kcal before exercise and 0.63 to 1.4 mg/1000 kcal during the exercise periods. Riboflavin requirement could not be related to the kilocalorie intake or lean body mass of the subjects. It is concluded that healthy young women require more riboflavin to achieve biochemical normality than the 1980 Recommended Dietary Allowances and that exercise increases riboflavin requirements.