W A Coward

Accuracy of weighed dietary records in studies of diet and health.

OBJECTIVE--To provide an independent evaluation of seven day weighed dietary records, which are currently accepted as the most accurate technique for assessing habitual dietary intake in studies investigating the links between diet and health. DESIGN--Subjects who had previously participated in the Northern Ireland diet and health study were reselected by stratified random sampling to represent the range of energy intakes in the study as assessed by the seven day weighed dietary record. SETTING--Northern Ireland. SUBJECTS--31 Free living adults (16 men and 15 women). MAIN OUTCOME MEASURES--Energy intake as measured by the seven day weighed dietary record and total energy expenditure estimated concurrently by the doubly labelled water technique. RESULTS--Average recorded energy intakes were significantly lower than measured expenditure in the group overall (9.66 MJ/day v 12.15 MJ/day, 95% confidence interval 1.45 to 3.53 MJ/day). Among those in the upper third of energy intakes the mean (SE) ratio of intake to expenditure was close to 1.0, indicating accurate records (men 1.01 (0.11), women 0.96 (0.08]. In the middle and lower thirds the ratios for men were only 0.74 (0.05) and 0.70 (0.07) respectively and for women 0.89 (0.07) and 0.61 (0.07). CONCLUSIONS--These results show a serious bias in reporting habitual energy intake. If substantiated they may have wide implications for the interpretation of many nutritional studies.

Helicobacter pylori Colonization in Early Life

Helicobacter pylori infection is a major cause of upper gastrointestinal disease throughout the world. Colonization begins in childhood, although little is known about its age of onset, rate, or mode of colonization. Our aim was to identify the age of acquisition of H. pylori colonization in Gambian children. A cohort of 248 Gambian children aged 3 to 45 months was studied at intervals of 3 months for 2 years, using the 13C-urea breath test, specific IgM and specific IgG serology. The prevalence of positive breath tests rose from 19% at 3 months of age to 84% by age 30 months. Elevated specific IgG and IgM antibody levels were associated with positive breath tests, although there was discrepancy between breath test results and serology, particularly IgG serology, during the 1st year of life. Neither IgG nor IgM serology could be validated as reliable diagnostic tools for infant H. pylori colonization compared with the 13C-urea breath test. Reversion to negative breath test, in association with declining specific antibody levels, occurred in 48/248 (20%) of children. On the assumption that the 13C-urea breath test is a reliable index of H. pylori colonization, we conclude that the infection is extremely common from an early age in Gambian children. Transient colonization may occur. Previous studies relying on serodiagnosis may have significantly underestimated the true early prevalence of colonization in the developing world, where the target age for intervention studies is probably early infancy.

Energy and fat intake in obese and lean children at varying risk of obesity.

OBJECTIVE: This study compared lean children at high risk (HR) and low risk (LR) of obesity and obese children (OB) to assess the relationship between their energy (EI) and fat intake and adiposity.DESIGN: Cross-sectional study of energy and fat intake in children, using 7-day weighed intakes validated by doubly labelled water (DLW) energy expenditure.SUBJECTS: A total of 114 pre-pubertal children, 50 HR (mean±s.d., 6.7±0.6 y, 25.7±4.8 kg, 21.3±6.6% body fat), 50 LR (mean±s.d., 6.6±0.8 y, 23.6±3.7 kg, 18.9±5.7% body fat) and 14 OB (mean±s.d., 6.8±1.0 y, 37.7±5.3 kg, 34.8±5.6% body fat).MEASUREMENTS: Body fatness was measured using deuterium dilution, total energy expenditure (TEE) by DLW and dietary intake using 7-day weighed records.RESULTS: EI was 98% of TEE in LR children, 95% in HR children and 86% in OB children. Although EI was similar in each group (LR, 7.03±1.26 MJ/day; HR, 7.30±1.46 MJ/day; OB, 7.55±1.67 MJ/day), obese children consumed more fat in absolute (g) and relative (percentage energy) terms than LR children (LR, 68±13 g, 36.4±4.2%; OB, 80±25 g, 39.5±4.6%; P<0.05). There was a significant linear trend towards increasing fat intake (percentage energy) with increasing risk of obesity (P<0.05). While HR children were heavier and fatter than LR children (P<0.05), their EI and fat intake were not significantly greater (HR, 73±17 g, 37.3±4.4%). Dietary fat intake (percentage energy) was weakly but significantly related to body fatness (r2=0.05, P=0.02) by step-wise regression. Since energy from fat was the only macronutrient that was a significant predictor of body fatness, results were therefore analysed using quartiles of fat intake (percentage energy) as cut-offs. When grouped in this way children with the lowest intakes were leaner than those with the highest intakes (19.5±7.5 vs 24.9±9.4% body fatness; P<0.05). There was a significant trend for increasing fatness as fat intake increased (P<0.05).CONCLUSION: Fat intake is related to body fatness in childhood.

Interpreting the 13C-urea breath test among a large population of young children from a developing country.

The 13C-urea breath test is a noninvasive tool for the diagnosis of gastric Helicobacter pylori infection. However, it has not been validated in young children from the developing world, where infection is very common. 13C urea breath tests were performed on 1532 occasions on 247 Gambian infants and children aged from 3 to 48 mo. The means and variances of the separate sub-populations of 13C enrichment results contained within the overall dataset were estimated by a Genstat procedure using the EM algorithm, thereby identifying a cut-off value to discriminate positive from negative results. To illustrate the appropriateness of this calculated cut-off value, 13C urea breath tests were performed upon a small group of 14 patients aged 6 to 28 mo undergoing diagnostic upper endoscopy. Fixed gastric antral biopsies were examined to identify H. pylori. Two sub-populations were identified within the large dataset. A cut-off value of 5.47 δ‰ relative to Pee Dee Belemnite limestone above baseline at 30 min identified 95% of the normally distributed negative sub-population and 99.4% of the log normal distributed positive sub-population. Comparison with endoscopic data confirmed that this cut-off value was appropriate for this population, as 7/7 children without H. pylori on their gastric biopsies had negative urea breath tests, and 6/7 children with gastric H. pylori colonization had positive urea breath tests. These findings confirm the value of the urea breath test as a diagnostic tool in young children from developing countries. They also offer a way to calculate the most appropriate cut-off value for use in different populations and the likelihood that it will correctly assign any value into the appropriate sub-population, without the need for endoscopy.

Starch Digestion in Young Children with Cystic Fibrosis Measured Using a 13C Breath Test

ABSTRACT: The study was designed to evaluate a non-invasive breath test using naturally 13C-rich corn (maize) as substrate to provide quantitative information about the digestion of starch by children in health and disease. The variability of background 13C:12C of young British children was investigated by collecting breath samples over 6 h from 17 healthy children, 6–35 mo old, and from seven children with cystic fibrosis, 25–48 mo old, in their homes. Background 13C enrichment was —26.6 and —25.4 d per mil in the healthy and cystic fibrosis groups, respectively (p <0.01), and varied little during the day (SD = 0.4 ± per mil). Eight healthy children and five with cystic fibrosis were given a test breakfast of corn starch cooked in milk with sugar. The cystic fibrosis group repeated the test with the addition of an enzyme supplement containing α-amylase. Subjects accepted variable amounts of starch (range 0.2–2.8 g/kg body wt). The percentage of ingested 13C recovered during the 6 h after the meal increased with age in the healthy children (range 15–53%). Three children with cystic fibrosis had negligible 13C recoveries, and the other two had lower recoveries than expected for their age. The addition of enzymes did not consistently improve 13C recovery. We conclude that the 13C breath test based on corn has potential for investigating starch digestion in young children. Initial results suggest that starch digestion is impaired in some children with cystic fibrosis and that enzyme supplements do not improve digestion consistently or completely.

Dose-response relationship between fat ingestion and oxidation: quantitative estimation using whole-body calorimetry and 13C isotope ratio mass spectrometry.

Objective: To determine dose-dependent relationship between ingested fat and its oxidation in the immediate post-prandial period in humans.Design: Subjects were randomly selected for the study at the Dunn Clinical Nutrition Centre, Cambridge, UK. Subjects ingested naturally enriched 13C corn-oil doses (range 20–140 g) in a whole-body indirect calorimeter, and were studied for 8 h. Ingested fat oxidation was estimated from the subjects breath 13C enrichment and total carbon dioxide production. Total fat and carbohydrate oxidation were estimated from non-protein oxygen and carbon dioxide exchanges. Endogenous fat oxidation was estimated as the difference between total fat and ingested fat oxidation.Results: The amount of fat dose oxidized was nonlinearly related to the amount ingested. On average, 25.6±2.7% of the mean fat dose was oxidized. A significant (r=−0.72, P<0.001) inverse correlation was found between the amount of fat dose and the proportion oxidized. Endogenous carbohydrate oxidation was negatively and significantly correlated to fat dose oxidized (r=−0.61, P<0.01), but it was not correlated to endogenous fat oxidation.Conclusions: There was a nonlinear relationship between amount of fat dose and its quantity that was oxidized in the immediate post-prandial period. The inverse relationship between the size of the fat load and the proportion that was oxidized post-prandially implies increased dietary fat storage beyond about 50 g in a normal resting adult. This has important implications for 13CO2-based studies.Sponsorship: This study was funded by the Nestle Foundation, Switzerland and the British Medical Research Council, UK.European Journal of Clinical Nutrition (2001) 55, 10–18

Energy Balance in Pregnancy and Lactation

The challenges of maintaining energy balance during human reproduction, and the various strategies which women adopt in order to achieve this, have been the topic of many previous reviews within this series of symposia (Prentice & Prentice, 1990; Coward et al., 1992; Forsum et al., 1992; Brown & Dewey, 1992) and elsewhere (eg Prentice & Whitehead, 1987; Durnin, 1987b). These have revealed an impressive level of knowledge regarding some of the fundamental issues such as changes in basal metabolic rate and in fat deposition, but a full interpretation has been constrained by the inability to measure all of the components of a woman’s daily energy budget. Recent methodological developments have removed this constraint.

Calcium intake of rural Gambian infants: a quantitative study of the relative contributions of breast milk and complementary foods at 3 and 12 months of age

BACKGROUND/OBJECTIVES:There is a paucity of information from developing countries on total calcium intake during infancy, and potential consequences for growth and bone development.DESIGN:Observational longitudinal study of rural Gambian infants (13 males and 17 females) at 3 and 12 months of age.SUBJECTS/METHODS:Breast-milk intake and calcium concentration, weighed dietary intake, anthropometry, midshaft radius bone mineral content (BMC) and bone width (BW).RESULTS:At 3 and 12 months (mean±s.d.) calcium intake from breast milk was 179±53 and 117±38, and from other foods 12±38 and 73±105 mg/day. There was no difference in total calcium intake; 94% and 62% of calcium came from breast milk. At 3 and 12 months, weight s.d.-scores were −0.441±1.07 and −1.967±1.06; length s.d.-scores were −0.511±1.04 and −1.469±1.13. Breast-milk calcium intake positively predicted weight (P=0.0002, P⩽0.0001) and length (P=0.056, P=0.001). These relationships were not independent of breast-milk intake, which positively predicted weight (P⩽0.002) and length (P=0.06, P=0.004). At 3, but not 12 months, weight and length correlated with total calcium intake. There were no relationships between total calcium intake and breast-milk intake with BW or BMC.CONCLUSION:The combination of low calcium intake from breast milk and complementary foods resulted in a low total calcium intake close to the estimated biological requirement for bone mineral accretion. Relationships between calcium intake and growth were largely accounted for by breast-milk intake, suggesting that low calcium intake per se was not the limiting factor in the poor growth. These findings have potential implications for deriving calcium requirements in developing countries.

Validity of published prediction equations for body composition in high altitude Bolivian Aymara as evaluated by doubly labeled water

Total body water (TBW), fat‐free mass (FFM), and fat as a percentage of body weight (fat%) were estimated by the doubly labeled water (DLW) technique in 23 healthy rural Bolivian subjects of a typical herding community of the high Andes. Using these values as the frame of reference, validation tests of several prediction equations for TBW and body density were made. Estimated values and errors for TBW, FFM, and fat% varied greatly with prediction equation. Among the prediction equations tested, however, three, Mellits and Cheek (1970; M&C), Durnin and Womersley (1974; D&W) and Conlisk et al. (1992; CNL), had a smaller bias and higher precision than others. Compared to the DLW method, the prediction errors of these equations for FFM and fat% as evaluated by the mean bias and the 95% limits of agreement were −0.7 ± 4.5 kg and 1.5 ± 10% (M&C), 0.9 ± 3.6 kg and −2.1 ± 8.5% (D&W), and 1.1 ± 3.6 kg and −2.7 ± 9.3% (CNL). For most practical purposes, these prediction errors for FFM as percentage of body weight may not be very important, but the errors in fat% may be serious. The interpretation of predicted data thus needs caution. In spite of differences in ethnic background and age range between the subjects and the samples on which the equations were developed, it is interesting that regression equations based on U.S., British and Guatemalan subjects also predicted the body composition of native Bolivian subjects with unexpectedly high precision. Am. J. Hum. Biol. 10:371–384, 1998.

Prediction of total body water and fatness from anthropometry: Importance of skinfold measurements

Prediction equations for total body water (TBW) generally use weight and height as predictors, but their ability may be limited because they implicitly assume a constancy of TBW among individuals of similar body size. The objective of this study was to evaluate the relative importance of anthropometric dimensions in predicting TBW and body composition. TBW determined by doubly labeled water (DLW) dilution techniques was used as the frame of reference in 23 healthy Aymara subjects, 4–65 years, in a rural community of the Bolivian Andes. Predictive performances of anthropometric variables for TBW were examined with multiple regression analyses. The generated equations were tested for cross‐validity, using published data for U.S. adults. The resulting errors were compared with those of the published prediction equations of Mellits and Cheek (M&C) and Durnin and Womersley (D&W). The simplified prediction equation using weight and the triceps skinfold (Eq‐A1:R2 = 0.989, SEE = 1.041 L) and that using weight and the triceps and subscapular skinfolds (Eq‐A2: R2 = 0.990, SEE = 1.020 L) had better R2 and smaller SEE than those using any combination of variables, weight, height, age, and sex. In the cross‐validation sample, Eq‐A1 and Eq‐A2 demonstrated higher precision than the D&W and M&C equations. Evaluated by the method of Bland and Altman (mean difference ± 2SD), prediction errors for fat mass and fat percent were 0.2 ± 2.8 kg and 0.4 ± 5.2% in Eq‐A2, 1.1 ± 3.5 kg, and 1.8 ± 6.1% in Eq‐A1, −2.4 ± 3.6 kg and −3.4 ± 5.1% in D&W, and −2.3 ± 7.6 kg and −2.6 ± 10.3% in M&C. Significant underestimation of fat mass and sex differences in the biases were observed with D&W and M&C (P < 0.05), but not with Eq‐A2. By including skinfold measurements, a single prediction equation for TBW was valid for males and females across different population samples.