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Biomedical subjects

A M Prentice

Publications and source records attributed to A M Prentice.

At least 127 records · Page 7Linked to original sources
PubMed1991

Longitudinal assessment of the components of energy balance in well-nourished lactating women.

The mechanisms by which well-nourished women meet the additional energy costs of lactation were studied by measuring energy intake (EI), basal metabolic rate (BMR), total energy expenditure by doubly labeled water (TEE), physical activity plus thermogenesis (TEE-BMR), changes in body fat stores, and milk energy transfer. Ten women were studied at 36 wk gestation; 4, 8, and 12 wk lactation (L4, L8, L12); and when nonpregnant and nonlactating (NPNL) after weaning. At L4, L8, and L12 the energy transferred in milk averaged 2245, 2225, and 2217 kJ/d with an additional 445 kj/d (106 kcal/d) estimated as being necessary for synthesis. EI was 1360, 1740, and 1275 kJ/d higher than the NPNL values, representing 56% of the costs of lactation. The remaining 44% was met by a reduction in TEE (-945, -688, and -826 kJ/d vs NPNL) caused largely by a reduction in physical activity because BMR was essentially unchanged (+29, -12, and -218 kJ/d). The energy-balancing strategies adopted by different women varied markedly.

Basal Metabolism↗
PubMed1991

Can maternal dietary supplements help in preventing infant malnutrition?

Many nutritional intervention programmes throughout the world have targeted food supplements towards women during the "at risk" periods of pregnancy and lactation. Some of these programmes, together with a number of small-scale scientific studies, have attempted to evaluate the efficacy of supplementation in terms of birth outcome or lactational performance. After reviewing the available evidence it is concluded: (a) that supplementation during late pregnancy can have a significant beneficial effect on birthweight in women who are genuinely "at risk" due to an inadequate home diet; (b) that statistical projections would predict that the increase in birthweight should be accompanied by a significant decrease in neonatal mortality; (c) that supplementation during lactation is most unlikely to increase breast-milk output or significantly improve its composition except perhaps in extremely malnourished women. Since pregnant women form a small and easily identifiable target group, and since the potential benefits of extra food may be substantial, it is recommended that future efforts are focussed in this direction. Large-scale effectiveness and cost-benefit trials are required with neonatal mortality as the primary outcome.

Developing Countries↗
PubMed1991

Free-living energy expenditure measured by two independent techniques in pregnant and nonpregnant Gambian women.

Free-living energy expenditure (EE) was assessed in 37 young pregnant Gambian women at the 12th (n = 11, 53.5 +/- 1.7 kg), 24th (n = 14, 54.7 +/- 2.1 kg), and 36th (n = 12, 65.0 +/- 2.6 kg) wk of pregnancy and was compared with nonpregnant nonlactating (NPNL) control women (n = 12, 50.3 +/- 1.6 kg). The following two methods were used to assess EE: 1) the heart rate (HR) method using individual regression lines (HR vs EE) established at different activity levels in a respiration chamber and 2) the doubly labeled water (2H2(18)O) method in a subgroup of 25 pregnant and 7 control women. With the HR method the EE during the agricultural rainy season was found to be 2,408 +/- 87, 2,293 +/- 122, and 2,782 +/- 130 kcal/day at 12, 24, and 36 wk of gestation and were not significantly different from the control group (2,502 +/- 133 kcal/day). These findings were confirmed by the 2H2(18)O measurements, which failed to show any effect of pregnancy on EE. Expressed per unit body weight, the free-living EE was found to be lower (P less than 0.01 with 2H2(18)O method) at 36 wk of gestation than in the NPNL group. It is concluded that, in these Gambian women, energy-sparing mechanisms that contribute to meet the additional energy stress of gestation are operating during pregnancy (e.g., diminished spontaneous physical activity).

Adolescent↗
PubMed1991

Critical evaluation of energy intake data using fundamental principles of energy physiology: 1. Derivation of cut-off limits to identify under-recording.

This paper uses fundamental principles of energy physiology to define minimum cut-off limits for energy intake below which a person of a given sex, age and body weight could not live a normal life-style. These have been derived from whole-body calorimeter and doubly-labelled water measurements in a wide range of healthy adults after due statistical allowance for intra- and interindividual variance. The tabulated cut-off limits, which depend on sample size and duration of measurements, identify minimum plausible levels of energy expenditure expressed as a multiple of basal metabolic rate (BMR). CUT-OFF 1 tests whether reported energy intake measurements can be representative of long-term habitual intake. It is set at 1.35 x BMR for cases where BMR has been measured rather than predicted. CUT-OFF 2 tests whether reported energy intakes are a plausible measure of the food consumed during the actual measurement period, and is always more liberal than CUT-OFF 1 since it has to allow for the known measurement imprecision arising from the high level of day-to-day variability in food intake. The cut-off limits can be used to evaluate energy intake data. Results falling below these limits must be recognized as being incompatible with long-term maintenance of energy balance and therefore with long-term survival.

Adult↗
PubMed1991

Critical evaluation of energy intake data using fundamental principles of energy physiology: 2. Evaluating the results of published surveys.

The fundamental principles of energy physiology were used to evaluate the validity of reported energy intake (EI) in 37 published dietary studies of adults providing 68 subgroups when classified according to sex and dietary method. EI was expressed as a multiple of BMR estimated using the reported heights and weights of the study populations (EI:BMR(est)). This ratio was compared with a study-specific cut-off value representing the lowest value for EI:BMR(est) that could, within defined bounds of statistical probability, reflect the habitual energy expenditure of a sedentary life-style. Mean EI:BMR(est) was 1.43 (0.19) compared with an expected requirement of 1.55. In 46 out of the 68 groups (68%), EI:BMR(est) was below the study-specific cut-off value. EI:BMR(est) was 1.37 (SD = 0.13) for women and 1.50 (SD = 0.16) for men (P less than 0.001). This could reflect either better reporting by men or a more active life-style. When categorized according to dietary assessment method, 64%, 88% and 25% of results fell below the acceptable cut-off value for studies by diet records, diet recall and diet history, respectively. These data indicate that dietary assessment methods have a strong bias towards underestimation of habitual energy intake.

Adolescent↗
PubMed1991

Effects of weight cycling caused by intermittent dieting on metabolic rate and body composition in obese women.

The effects of repeated periods of weight loss and regain on metabolic rate and body composition were investigated in 11 obese women (mean weight 81.98 kg, height 1.61 m, body mass index 31.44 kg/m2) studied for 18 weeks through three consecutive cycles of 2 weeks dieting followed by 4 weeks ad libitum eating. Weight loss was achieved by a very low energy diet (1861 kJ/day). Basal metabolic rate (BMR) was measured by whole-body indirect calorimetry and body composition by a variety of standard in vivo methods. During the three diet periods mean weight losses were 4.44, 3.29 and 2.98 kg although the mean overall weight loss from week 0 to 18 was only 5.93 kg. The proportion of weight lost as fat was estimated as between 67 and 105 per cent of the weight lost depending on the body composition methodology employed. Absolute BMR decreased in response to dieting by 545, 285 and 286 kJ/day. When corrected for body weight and FFM only the decreases in the first diet period were significant (P less than 0.05 and P less than 0.001 respectively). BMR had returned to normal following each 4-week ad libitum period and by the end of the study absolute BMR and BMR/kg FFM had not changed significantly, despite a significant loss of weight. Consequently BMR/kg was increased (P less than 0.01), indicative of the loss of adipose tissue. We have found no evidence in this group of obese women that weight cycling leads to a progressive decrease in BMR or increase in the proportion of body fat.

Adipose Tissue↗
PubMed1990

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.

Adolescent↗
PubMed1990

Simultaneous measurement of free-living energy expenditure by the doubly labeled water method and heart-rate monitoring.

Total energy expenditure (TEE) was measured simultaneously in 14 free-living adults over 15 d by the doubly labeled water (DLW) method and for 2-4 separate days by heart-rate (HR) monitoring. Individual curves for HR vs oxygen consumption (VO2) were obtained and an HR (FLEX HR: 97 +/- 8 beats/min, range 84-113 beats/min) that discriminated between rest and activity was identified. Calibration curves were used to assign an energy value to daytime HR above FLEX HR. Below FLEX HR energy expenditure was taken as resting metabolism. Sleeping energy expenditure was assumed to be equal to basal metabolic rate. Average HR TEE (12.99 +/- 3.83 MJ/d) and average DLW TEE (12.89 +/- 3.80 MJ/d) were similar. HR TEE discrepancies ranged from -22.2% to +52.1%, with nine values lying within +/- 10% of DLW TEE estimates. The FLEX HR method provides a close estimation of the TEE of population groups. However, an increased number of sampling days may improve the precision of individual estimates of TEE.

Activities of Daily Living↗
PubMed1990

Residual effect of graded levels of exercise on metabolic rate.

The hypothesis that exercise induces a residual effect on metabolic rate only when the intensity exceeds a certain threshold was tested by studying 10 healthy, untrained adults performing graded levels of bicycle ergometry on five separate occasions. The exercise consisted of four 30-min periods at intensities ranging from 0 to 100 Watts. Energy expenditure was measured by continuous indirect whole-body calorimetry. The highest level of exercise increased 24-h energy expenditure by 34 per cent. Food intake was modified for each measurement in order to maintain energy balance. Sleeping and basal metabolic rates on the night following exercise were raised even at low intensities of exercise. There was an almost linear dose-response relationship and no evidence of a threshold. However, the effect was small, amounting to only 5.8 per cent overnight and 3.9 per cent in the morning following 2 h exercise at over 60 per cent VO2 max during the preceding day. This suggests that the residual energy expenditure incurred after moderate levels of exercise is unlikely to be a very useful adjunct to slimming regimes.

Adult↗
PubMed1989

Energy-sparing adaptations in human pregnancy assessed by whole-body calorimetry.

The hypothesis that the energy cost of human pregnancy can be minimized by energy-sparing metabolic adaptations was tested using serial 24 h whole-body calorimetry. Eight healthy, well-nourished women were studied prepregnant and at 6, 12, 18, 24, 30 and 36 weeks gestation. Basal metabolic rate (BMR) showed highly characteristic changes within each subject and large inter-individual differences (F 3.5, P less than 0.01). Some subjects showed a highly significant depression of metabolism up to 24 weeks gestation in support of the initial hypothesis. At 36 weeks BMR ranged from +8.6 to +35.4% relative to the prepregnant baseline. This wide variability was not explained by differences in the amount of lean tissue gained. Women displaying the energy-sparing suppression of BMR tended to be thin, suggesting that changes in metabolism may be responsive to initial energy status (delta BMR v. prepregnant body fat: r 0.84, P less than 0.005). Changes in 24 h energy expenditure closely paralleled changes in BMR (r 0.98, P less than 0.001), since the energy cost of minor voluntary activity and thermogenesis remained very constant within each individual. Pregnancy decreased the net cost of weight-dependent and weight-independent standard exercises when expressed per kg body-weight: stepping -10 (SD 2)%, P less than 0.001 at 18-36 weeks, cycling -26 (SD 7)%, P less than 0.01 at 12-36 weeks. The average integrated maintenance costs of pregnancy matched previous group estimates from well-nourished women, but individual estimates ranged from -16 to +276 MJ (coefficient of variation 93%). This high level of variability has important implications for the prescription of incremental energy intakes during pregnancy. It may also have had evolutionary significance.

Adaptation, Physiological↗
PubMed1989

Energy expenditure of Gambian women during peak agricultural activity measured by the doubly-labelled water method.

The doubly-labelled water (2H218O) method was used to measure total energy expenditure (TEE) in ten non-pregnant, non-lactating (NPNL), six pregnant (P) and fourteen lactating (L) women in a rural Gambian community. Measurements were made on free-living subjects at a period of peak energetic stress when high agricultural work loads coincided with a hungary season to induce moderately severe negative energy balance. TEE averaged 10.42 (SD 2.08) MJ/d, equivalent to 1.95 (SD 0.38) times resting metabolic rate (RMR). The energy cost of physical activity plus thermogenesis, derived as TEE-RMR, averaged 4.94 (SD 1.96) MJ/d. Expressed per kg body-weight (103 kJ/kg per d) this component of expenditure was 2.5 times greater than comparative values from inactive, affluent women studied previously (39 kJ/kg per d). Estimated energy intake (EI) in a subset of the women (n 13) was only 4.80 (SD 1.58) MJ/d, yielding an apparent deficit of 6.08 MJ/d between EI and TEE. Weight changes suggested that endogenous fat oxidation accounted for only about 0.85 MJ/d, leaving an unexplained difference of over 5 MJ/d. Critical analysis of possible errors suggests that the new doubly-labelled water method has provided the most reliable estimates and that the estimates of EI were substantially in error. This finding has important consequences for other food intake studies.

Adult↗
PubMed1989

The effect of exercise and improved physical fitness on basal metabolic rate.

1. The suggestion that there is a sustained enhancement in metabolic rate after exercise was investigated during the course of a study in which six normal-weight volunteers (three men, three women) took part in a 9-week training programme. Baseline values were assessed in a 3-5 week control period of minimal activity before training. At the end of the study the subjects were capable of running for 1 h/d, 5 d/week. 2. Throughout the entire study the subjects were maintained on a constant diet. Measurement of energy expenditure by the doubly-labelled water (2H2(18)O) method showed that the subjects had an energy imbalance of +3% in the control and -20% at the end of the training period. The subjects were in positive (1.1 (SE 0.2) g) nitrogen balance in the second week of the control, and in negative (-0.6 (SE 0.3) g) N balance in the last week of the exercise period. 3. Over the course of the study maximum oxygen consumption (VO2max) and high-density-lipoprotein-cholesterol levels increased by 30%. Heart rate at rest and when performing a standard step test fell significantly. 4. Body composition was assessed weekly by 40K counting and skinfold thickness measurements, in addition to 2H2 dilution at the beginning and end of the study. Fat-free mass was apparently gained in the early phases of the study, but there was lack of agreement between the different methods of assessing body composition. Changes in body-weight were not significant. 5. Basal metabolic rate (BMR), overnight metabolic rate (OMR) and sleeping metabolic rate (SMR) were measured on three occasions: in the control period, and the beginning and end of the training periods. Average BMR in the control period was 5.91 (SE 0.39) MJ/24 h and was not changed with activity. There were no changes in OMR (5.71 (SE 0.27) MJ/24 h in the control) nor in SMR (5.18 (SE 0.27) MJ/24 h in the control), nor in BMR, OMR or SMR when expressed per kg body-weight, or per kg fat-free mass. 6. These results do not support the suggestions that there is a sustained increase in BMR following exercise that can usefully assist in weight-loss programmes.

Adult↗
PubMed1989

The use of heart rate monitoring in the estimation of energy expenditure: a validation study using indirect whole-body calorimetry.

1. A modified heart rate (HR) method for predicting total energy expenditure (TEE) was cross-validated against whole-body calorimetry (CAL). Minute-by-minute HR was converted to energy expenditure (EE) using individual calibration curves when HR exceeded a pre-determined 'FLEX' value designed to discriminate periods of activity. ('FLEX' HR was defined as the mean of the highest HR during rest and the lowest HR during the lightest imposed exercise.) Sedentary EE (below FLEX) was calculated as the mean EE during lying down, sitting and standing at rest. Sleeping EE was calculated as basal metabolic rate (BMR) predicted from standard equations. 2. Calibration curves of oxygen consumption v. HR for different postures at rest and during exercise were obtained for twenty healthy subjects (eleven male, nine female); mean r 0.941 (SD 0.04). The mean FLEX HR for men and women were 86 (SD 10) and 96 (SD 6) beats/min respectively. 3. Simultaneous measurements of HR and EE were made during 21 h continuous CAL, which included 4 x 30 min imposed exercise (cycling, rowing, stepping, jogging). HR exceeded FLEX for a mean of 98 (SD 41) min. Mean TEE by CAL (TEE.CAL) was 8063 (SD 1445) kJ. 4. The HR method yielded a mean non-significant underestimate in TEE (TEE.HR) of 1.2 (SD 6.2)% (range -11.4 to +10.6%). Regression of TEE.HR (Y) v. TEE.CAL (X) yielded Y = 0.868 X + 927 kJ, r 0.943, SE of the estimate 458 kJ, n 20. 5. The satisfactory predictive power and low cost of the method makes it suitable for many field and epidemiological applications.

Adolescent↗
PubMed1989

Is severe wasting in elderly mental patients caused by an excessive energy requirement?

Many chronically ill mental patients show rapid and severe weight loss leading to severe nutritional debilitation. Excessive energy requirements secondary to hypermetabolism or hyperactivity have been proposed as the cause. This hypothesis was tested using the new doubly-labelled water (2H218O) technique to obtain accurate estimates of total energy expenditure (TEE) in 14 such patients. Mean TEE was very low (6.1 +/- 1.3 MJ/day). None of the subjects was in significant negative energy balance when studied. Mean resting metabolic rate (RMR) was lower than predicted from standard equations based on healthy elderly subjects. The energy cost of physical activity plus thermogenesis was also low (1.7 +/- 0.9 MJ/day) in all except one subject. The data refute the initial hypothesis and suggest that negative energy balance may be episodic, perhaps during periods of infection and subsequent recovery.

Aged↗
PubMed1988

Are current dietary guidelines for young children a prescription for overfeeding?

New estimates for the energy requirements of young children have been derived by combining the energy deposited during growth with measurements of total energy expenditure obtained by use of the new doubly-labelled water (2H2(18)O) method in 355 healthy infants aged 0-3 years. The resultant values of 110, 95, 85, 83, 83, 84, and 85 kcal/kg/day at 1, 3, 6, 9, 12, 24, and 36 months, respectively, are substantially lower than current Department of Health and Social Security and FAO/WHO/UNU recommended dietary allowances. Evidence from diet surveys suggests that changes in infant feeding practices are largely responsible for the apparent reduction in energy requirements. Dietary guidelines may need to be reappraised, to avoid overfeeding of infants.

Age Factors↗