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Biomedical subjects

A M Prentice

Publications and source records attributed to A M Prentice.

At least 109 records · Page 6Linked to original sources
PubMed1993

Energy balance in healthy elderly women.

There is a paucity of data on which to base estimates of the energy requirements of the elderly. In general, ageing appears to be associated with a reduction in energy requirement arising from a reduction in physical activity and loss of fat-free mass. The aim of the present study was to measure the total energy expenditure (TEE), basal metabolic rate (BMR), and energy expended on physical activity (calculated as TEE-BMR) in a group of healthy elderly women living in the community in Southampton. Mean rates of TEE (9.21 (SD 1.48) MJ/d) and energy expended on physical activity (4.12 (SD 1.19) MJ/d) were higher than those observed in some studies of younger adults in the UK, and higher than the factors used to estimate the average energy requirement for the elderly. The results suggest that an age-related reduction in energy requirement is not inevitable and support the hypothesis that the effects of ageing on physical activity, body composition, and hence energy requirements, are variable.

Aged↗
PubMed1993

Evidence of energy sparing in Gambian women during pregnancy: a longitudinal study using whole-body calorimetry.

Components of daily energy expenditure were measured serially by whole-body calorimetry in Gambian women before pregnancy and at 6, 12, 18, 24, 30, and 36 wk gestation. Weight gain was (mean +/- SD) 6.8 +/- 2.8 kg, fat deposition was 2.0 +/- 2.5 kg and lean tissue deposition was 5.0 +/- 2.5 kg. Basal metabolic rate (BMR) was depressed during the first 18 wk of gestation, causing total cumulative maintenance costs by week 36 to be 8.4 MJ. Individual responses to pregnancy correlated with changes in body mass (36 wk: delta BMR vs delta weight; r = 0.60, P < 0.01 delta BMR vs delta LBM; r = 0.62, P < 0.01). There was no significant increase in the cost of treadmill exercise (0% slope: F = 0.71, P = 0.64; 5% slope: F = 1.97, P = 0.10), 24-h energy expenditure (F = 0.72, P = 0.64), activity or diet-induced thermogenesis (F = 1.02, P = 0.43), during pregnancy in spite of body weight gain. Total metabolic costs over 36 wk were 144 MJ (fetus 43 MJ, fat deposition 92 MJ, cumulative maintenance costs 8.4 MJ). These were far lower than reported for well-nourished Western populations.

Adipose Tissue↗
PubMed1993

Longitudinal assessment of energy expenditure in pregnancy by the doubly labeled water method.

Twelve women were studied before pregnancy and at 6-wk intervals from 6 to 36 wk gestation. Total energy expenditure (TEE) by the doubly labeled water method, basal metabolic rate (BMR), energy intake, and body composition were assessed on each occasion. There was substantial interindividual variation in the response to pregnancy. Mean total energy costs were as follows: delta BMR 112 +/- 104 MJ (range -53 to 273), delta TEE 243 +/- 279 MJ (range -61 to 869 MJ), and fat deposition 132 +/- 127 MJ (range -99 to 280 MJ). The mean total cost of pregnancy (cumulative TEE above baseline+energy deposited as fat and as products of conception) was 418 +/- 348 MJ (range 34-1192 MJ). This was much higher than current recommendations for incremental energy intakes. Self-recorded incremental intakes (208 +/- 272 MJ) seriously underestimated the additional costs. The variability in response emphasizes the problems in making prescriptive recommendations for individual women, because there is no way of predicting metabolic or behavioral responses to pregnancy.

Adult↗
PubMed1993

Carbohydrate balance and the regulation of day-to-day food intake in humans.

The hypothesis that carbohydrate stores are an important determinant of voluntary food intake was tested by covert dietary manipulation of carbohydrate stores in nine men during 2 d of continuous whole-body calorimetry that provided half-hourly monitoring of energy and fuel balance. On day 1 subjects were fed diets intended to maintain energy balance but containing carbohydrate at either 3% (depletion) or 47% (control) energy. Average carbohydrate balance changed by 153 +/- 42 g (mean +/- SD). Subsequent (day 2) ad libitum food intake from a normal diet of fixed macronutrient composition was identical on the control and depletion protocols: 12.73 +/- 2.24 and 12.72 +/- 2.01 MJ, respectively. The carbohydrate-depletion protocol caused a suppression of carbohydrate oxidation (174 +/- 41 vs 256 +/- 39 g, P < 0.001) and a reciprocal elevation in fat oxidation (120 +/- 11 vs 89 +/- 12 g, P < 0.001). These readjustments in fuel utilization were the primary mechanism for re-establishing carbohydrate balance. This study does not support the hypothesis that the need to maintain specific carbohydrate stores is a determinant of food intake in the short term.

Adult↗
PubMed1993

In vivo measurement of changes in body composition: description of methods and their validation against 12-d continuous whole-body calorimetry.

The accuracy of a variety of in vivo body-composition techniques (densitometry, total body water, skinfold thicknesses, whole-body impedance and resistance, body mass index, and two three-compartment models) was assessed by comparison with fat balance. Three subjects were overfed and three underfed while confined to a 30-m3 whole-body calorimeter continuously for 12 d. Mean weight changes were +2.90 kg during overfeeding and -3.47 kg during underfeeding. The change in fat mass accounted for 37.1% during overfeeding and 59.3% during underfeeding. In comparison with energy and nitrogen balance, a three-compartment model yielded the least bias and greatest precision. The smallest change in fat mass that can be measured by such a method in an individual subject is 1.54 kg (2 SD). Of the prediction techniques considered, skinfold thicknesses or the body-mass-index formula appear to be more precise than estimates based on resistance or impedance.

Adolescent↗
PubMed1993

Non-invasive techniques for assessing carbohydrate flux: I. Measurement of depletion by indirect calorimetry.

Glycogen forms the smallest yet most labile energy substrate store. Therefore studying carbohydrate flux may be crucial to understanding the regulation of energy balance. Indirect calorimetry has been used to measure carbohydrate oxidation overnight and during exercise in nine fasted subjects. Overnight carbohydrate oxidation (averaging 2.85 +/- 0.8 g h-1) was assumed to be derived primarily from hepatic glycogen since subjects were inactive or asleep, and since glucose oxidized after gluconeogenesis from protein is measured as protein oxidation. Lower-limb muscle glycogen stores were depleted by repeated 30-min periods of cycle ergometry at 45% VO2max until exhaustion (8 +/- 1 periods). The carbohydrate oxidation rate decreased as exercise progressed. Quadratic curves yielded a close fit to each individual's exercise carbohydrate depletion data (mean multiple correlation r = 0.9996) and provided excellent inter-subject discrimination. Total (muscle plus liver) glycogen stores prior to exercise were estimated by extrapolation of the depletion curves to zero oxidation rate. This produced an extrapolation of the depletion curves to zero oxidation rate. This produced an estimate (174 +/- 61 g) which compared well with predictions (208 +/- 43 g) based on reference values for muscle mass and initial glycogen content. The results demonstrate that non-invasive estimates of glycogen status can be obtained from accurate respiratory exchange data.

Adult↗
PubMed1993

Non-invasive techniques for assessing carbohydrate flux: II. Measurement of deposition using 13C-glucose.

A non-invasive method for studying the dynamics of post-exercise carbohydrate storage by means of whole-body calorimetry and 13CO2 breath tests is described. Seven untrained glycogen-depleted subjects were offered naturally 13C-labelled high carbohydrate meals (97% by energy) at 30 min intervals for 5 h and asked to consume as much as possible. Mean intake averaged 757 +/- 211 (SD) g. Exogenous carbohydrate oxidation over 16 h calculated from gas exchange and isotope ratio measurements averaged 161 +/- 45 g, and endogenous carbohydrate oxidation averaged 31 +/- 25 g. Net carbohydrate storage, calculated as the difference between amount ingested and oxidized, was 563 g which was more than twice the measured hepatic and muscle carbohydrate oxidized during the depletion phase. After correction for body size the major determinant of glycogen storage was the amount of carbohydrate consumed (r = 0.97, P < 0.001) which in turn was determined by each subject's dietary tolerance. Post-repletion exercises (12 h after last meal) were used to remobilize freshly stored glycogen. 13CO2 enrichments indicated that a substantial part of the new glycogen was derived from the exogenous carbohydrate provided by the repletion meals.

Adult↗
PubMed1993

Techniques for the measurement of human energy expenditure: a practical guide.

We have tried to provide a brief guide to the range of techniques available for assessing energy expenditure in a variety of different settings. It is hoped that this will enable potential users to select an appropriate method for the problem in hand and to be able to trace more detailed reference material, advice or collaboration. The Appendix provides a selection of equipment suppliers known to us. It is not an exhaustive list. Many laboratories which possess some of the more elite techniques are prepared to participate in collaborative studies if approached with a sufficiently novel hypothesis or clinical problem. Since many biological questions will only be solved by harnessing the combined power of several techniques (e.g. whole-body calorimetry and DLW), such collaborative studies are often beneficial.

Calorimetry↗
PubMed1992

Effects of weight cycling on body composition.

It is frequently claimed that weight cycling, or "yo-yo" dieting, causes an inappropriate and permanent loss of lean body mass (LBM). Data are presented from a rural African population that undergoes profound weight cycling caused by an annual hungry season. No detrimental effect on LBM was observed. Data are also presented from an 18-wk prospective study of moderately obese British women who underwent three cycles of VLCD-induced weight loss and subsequent relapse. The proportion of weight lost as LBM was no greater than predicted. A review of the published results from experimental weight cycling in small animals also shows a high level of consensus that cycling does not significantly alter body composition. We conclude that, although weight cycling may affect growth of young animals, metabolic efficiency, and health, these effects are not mediated through permanent alterations in body composition.

Adipose Tissue↗
PubMed1992

Validation of estimates of energy intake by weighed dietary record and diet history in children and adolescents.

Energy intakes assessed by 7-d weighted dietary records (EI-WDRs) and diet histories (EI-DHs) were compared with concurrent estimates of total energy expenditure (TEE) by the doubly labeled water method in 78 subjects aged 3-18 y. EI-WDRs were not obtained from the 3- and 5-y-old subjects. EI-WDRs in the 7- and 9-y-old children were 108 +/- 25% (n = 12) and 97 +/- 15% (n = 12), respectively, of corresponding TEE values showing good agreement. However in the 12-, 15-, and 18-y-old subjects EI-WDR averaged 89 +/- 12% (n = 12), 78 +/- 18% (n = 12), and 73 +/- 25% (n = 10), respectively, of corresponding TEE values. The difference was greater than or equal to 20% in 13 adolescents. Mean EI-DHs were 114 +/- 19% (3 y), 111 +/- 19% (5 y), 111 +/- 23% (7 y), 106 +/- 9% (9 y), 114 +/- 17% (12 y), 101 +/- 21% (15 y), and 98 +/- 21% (18 y) of TEE estimates. Differences were significant in the 3-, 9-, and 12-y-old subjects. Results suggest that 7-d EI-WDRs tend to underestimate food intake of adolescents. Although EI-DHs were biased towards overestimation in most age groups and individual measurements lacked precision, EI-DHs were more representative of habitual intake than were EI-WDRs.

Adolescent↗
PubMed1992

Daily energy expenditure in free-living children: comparison of heart-rate monitoring with the doubly labeled water (2H2(18)O) method.

Total energy expenditure (TEE) was measured simultaneously in 36 free-living children aged 7, 9, 12, and 15 y over 10-15 d by the doubly labeled water (DLW) method and for 2-3 separate days by heart-rate (HR) monitoring. The 95% confidence limits of agreement (mean difference +/- 2SD) were -1.99 to +1.44 MJ/d. HR TEE discrepancies ranged from -16.7% to +18.8% with 23 values lying within +/- 10% of DLW TEE estimates. Boys and girls spent 462 +/- 108 and 318 +/- 120 min/d, respectively, in total physical activity (P less than 0.01). Time spent in moderate and vigorous physical activity (MVPA) was 68 +/- 37 min/d by younger children (7-9 y) and 34 +/- 24 min/d by older children (12-15 y) (P less than 0.001). Younger boys engaged in MVPA (91 +/- 33 min/d) and vigorous physical activity (VPA) (35 +/- 15 min/d) significantly longer than younger girls (MVPA, 39 +/- 16 min/d, P less than 0.001; VPA, 10 +/- 4 min/d, P less than 0.01) as did older boys (MVPA, 52 +/- 21 min/d; VPA, 30 +/- 18 min/d) compared with older girls (MVPA, 15 +/- 10 min/d; VPA, 8 +/- 5 min/d). HR monitoring provides a close estimation of the TEE of population groups and objective assessment of associated patterns of physical activity.

Adolescent↗
PubMed1992

Metabolic response to experimental overfeeding in lean and overweight healthy volunteers.

Possible adaptive mechanisms that may defend against weight gain during periods of excessive energy intake were investigated by overfeeding six lean and three overweight young men by 50% above baseline requirements with a mixed diet for 42 d [6.2 +/- 1.9 MJ/d (mean +/- SD), or a total of 265 +/- 45 MJ]. Mean weight gain was 7.6 +/- 1.6 kg (58 +/- 18% fat). The energy cost of tissue deposition (28.7 +/- 4.4 MJ/kg) matched the theoretical cost (26.0 MJ/kg). Basal metabolic rate (BMR) increased by 0.9 +/- 0.4 MJ/d and daily energy expenditure assessed by whole-body calorimetry (CAL EE) increased by 1.8 +/- 0.5 MJ/d. Total free-living energy expenditure (TEE) measured by doubly labeled water increased by 1.4 +/- 2.0 MJ/d. Activity and thermogenesis (computed as CAL EE--BMR and TEE--BMR) increased by only 0.9 +/- 0.4 and 0.9 +/- 2.1 MJ/d, respectively. All outcomes were consistent with theoretical changes due to the increased fat-free mass, body weight, and energy intake. There was no evidence of any active energy-dissipating mechanisms.

Basal Metabolism↗
PubMed1991

Potential contribution of leisure activity to the energy expenditure patterns of sedentary populations.

Total daily energy expenditure (TEE) by the doubly-labelled (2H218O) water method and basal metabolic rate (BMR) by indirect calorimetry were measured in thirty-two healty free-living adults in Northern Ireland. Habitual physical activity patterns in occupational and discretionary activities were assessed by interview questionnaire. Expressed as a multiple of BMR the TEE values for the sixteen males (1.88 (SD 0.28), range 1.44-2.57) and sixteen females (1.77 (SD 0.16), range 1.50-2.06) were compatible with current Department of Health and Social Security (DHSS; 1979) and Food and Agriculture Organization/World Health Organization/United Nations University (FAO/WHO/UNU; 1985) estimates of energy requirements. The results suggest that discretionary physical activity is now emerging as an equally important determinant of energy expenditure in the UK as the occupational classifications currently used as the basis of DHSS (1979) and FAO/WHO/UNU (1985) recommendations for energy requirements. Therefore, realistically achievable inputs of recreational exercise can have a significant impact in counteracting low levels of energy expenditure which are associated with modern lifestyles and are implicated as a risk factor for coronary heart disease and obesity.

Adult↗
PubMed1991

Effects of dietary supplementation on work performance in Gambian laborers.

The effect of food supplementation on productivity of Gambian subsistence farmers was studied during a natural food shortage induced by the annual hungry season. Sixteen men in two groups matched for weight, height, hemoglobin, and physical-work capacity followed a crossover protocol with 6-wk supplementation and control periods. Productivity was assessed over the final 3 wk of each period by quantifying piece-rate-paid road building. Supplementation comprised an ad libitum supply of highly palatable energy-dense food provided three times daily. Outcome variables were total loads transported, loads per working hour, time per load, total energy expenditure assessed by doubly labeled water and heart-rate monitoring, postwork activity, and anthropometry. Body weight decreased during control periods, indicating a real energy deficit, and increased during supplementation in both groups. Supplementation had no significant impact on productivity variables. Energy-deficient men can maintain maximal productivity over short periods if sufficiently motivated but at the expense of body weight.

Adult↗