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Biomedical subjects

A M Prentice

Publications and source records attributed to A M Prentice.

At least 19 recordsLinked to original sources
PubMed2006

Frequent feeding delays the gastric emptying of a subsequent meal.

To assess the suitability of the 13C-octanoic acid breath test for measuring gastric emptying in circumstances other than the post-absorptive state, a preliminary study was performed where 6 hourly spaced isoenergetic meals preceded the determination of gastric emptying of a subsequent 2 MJ meal. Emptying was measured in three individuals on four separate occasions, with a reproducibility of 8%. A crossover study was then conducted to test the hypothesis that meal frequency can modulate the gastric emptying of a subsequent meal, with the potential to influence appetite regulation. Sixteen subjects were fed to energy balance, receiving food either as 2 isoenergetic meals 3 h apart or 6 isoenergetic meals fed hourly. Gastric emptying of a subsequent 2 MJ meal was investigated. Visual analogue scales were used throughout to assess appetite. The maximum rate of gastric emptying was unchanged but the onset of emptying was delayed by the more frequent feeding pattern. There was no significant difference in subjective appetite before or after the test meal. In conclusion, short-term increases in feeding frequency delayed the gastric emptying of a subsequent meal, but significant effects on post-meal appetite could not be demonstrated.

Adult↗
PubMed2006

Validity of the leg-to-leg bioimpedance to estimate changes in body fat during weight loss and regain in overweight women: a comparison with multi-compartment models.

OBJECTIVES: To investigate changes in body composition and the validity of the leg-to-leg bioimpedance (LTL) method to measure body fat during active weight loss (WL) and weight regain (WR). DESIGN: Longitudinal, 12-week weight loss intervention (3.3-3.8 MJ/day) and subsequent follow-up at 1 year. SUBJECTS: Fifty-eight adult women aged between 24 and 65 years (mean age: 46.8+/-8.9 years) and with a body mass index (BMI) > or =25 kg/m(2) (mean BMI: 31.6+/-2.5 kg/m(2), range=26.0-48.2 kg/m(2)) participated in the study. MEASUREMENTS: Fat mass (FM) was measured at baseline, 12 weeks, 24 weeks and 52 weeks using three- and four-compartment (4-C) models, air displacement plethysmography (ADP), deuterium dilution - total body water (TBW), dual-energy X-ray absorptiometry (DXA), skinfold thickness (SFT), tetrapolar bioelectrical impedance analysis (T-BIA) and LTL. RESULTS: At the end of the weight loss programme, subjects lost 9.9+/-3.5 kg weight (P<0.001) and 7.6+/-0.5 kg fat (P<0.001) but after 1 year they had regained 4.9+/-3.7 kg of weight and 3.7+/-2.9 kg of fat. The 4-C model showed that FM and TBW accounted for 76.2 and 23.6% of the loss in body mass and 81.8 and 17.7% of the tissue accrued during weight regain, respectively. The estimate of body fat change by LTL relative to multi-compartment models (WL(bias+/-2s.d.)=0.51+/-3.26 kg; WR(bias+/-2s.d.)=-0.25+/-2.30 kg) was similar to ADP, DXA and TBW in both phases but it was better than T-BIA (WL(bias+/-2s.d.)=0.17+/-7.90 kg; WR(bias+/-2s.d.)=-0.29+/-7.59 kg) and skinfold thickness (WL(bias+/-2s.d.)=2.68+/-6.68 kg; WR(bias+/-2s.d.)=-0.84+/-3.80 kg). CONCLUSIONS: Weight loss and regain were associated with minimal changes in lean tissue as measured using multi-compartment models. The LTL system is a useful method to measure body composition changes during clinical weight management programmes.

Adipose Tissue↗
PubMed2006

Variability of appetite control mechanisms in response to 9 weeks of progressive overfeeding in humans.

BACKGROUND: The current epidemic of obesity demonstrates that mechanisms for maintaining human energy balance are readily subverted by adverse environmental conditions. The critical elements of this dysregulation are poorly understood. Most previous research into what regulates the intake side of the energy balance equation has been handicapped by the use of short-term within-day experimental tests. OBJECTIVE: We enrolled six non-obese men to a 17-week protocol involving three 21 days periods of progressive overfeeding (+20, +40 and +60%) separated by free diet periods to test for compensatory satiety. RESULTS: Responses to overfeeding differed markedly with evidence of 'compensators' and 'non-compensators', but on average, subsequent food intake was stimulated rather than suppressed after overfeeding in spite of markedly elevated body fat (+13%) and fasting leptin (+116%). DISCUSSION: The inefficient response of in-built appetite control mechanisms emphasizes the need to adopt intentional cognitive restraint in the modern environment when food is plentiful.

Adipose Tissue↗
PubMed2006

A pilot study on body image, attractiveness and body size in Gambians living in an urban community.

OBJECTIVE: We investigated the attitudinal and perceptual components of body image and its link with body mass index (BMI) in a sample of urban Gambians. We also looked at cross-cultural differences in body image and views on attractiveness between Gambians and Americans. METHODS: Four groups of 50 subjects were assessed: men 14- 25y (YM); women 14-25y (YW); men 35-50y (OM); women 35-50y (OW). Socio-economic status, education, healthy lifestyle and western influences were investigated. Height and weight were measured. Body dissatisfaction was assessed with the body dissatisfaction scale of the Eating Disorder Inventory. Perceptions of body image and attractiveness were assessed using the Body Image Assessment for Obesity (BIA-O) and Figure Rating Scale (FRS). RESULTS: Different generations of Gambians had very different perceptions and attitudes towards obesity. Current body size was realistically perceived and largely well tolerated. Older women had a higher body discrepancy (current minus ideal body size) than other groups (p<0.001). Regression analysis showed they were not worried about their body size until they were overweight (BMI=27.8 kg/m2), whilst OM, YM and YW started to be concerned at a BMI respectively of 22.9, 19.8 and 21.5 kg/m2. A cross-cultural comparison using published data on FRS showed that Gambians were more obesity tolerant than black and white Americans. DISCUSSION: The Gambia is a country in the early stage of demographic transitions but in urban areas there is an increase in obesity prevalence. Inherent tensions between the preservation of cultural values and traditional habits, and raising awareness of the risks of obesity, may limit health interventions to prevent weight gain.

Adolescent↗
PubMed2006

Urbanization and obesity in The Gambia: a country in the early stages of the demographic transition.

OBJECTIVE: To investigate the distribution of overweight and obesity and its relationship with socio-economic and behavioural factors in a developing-country population undergoing rapid nutritional transition. DESIGN: Cross-sectional house-to-house survey in urban Gambia. SUBJECTS: Four groups of 50 subjects were sampled as follows: young men (YM, 14-25 years), young women (YW, 14-25 years), older men (OM, 35-50 years) and older women (OW, 35-50 years). MEASUREMENTS: Several socio-economic and behavioural factors were investigated. Composite indices for socio-economic status, education, healthy lifestyle and western influences were created. Body weight, height, waist and hip circumferences were measured and body mass index (BMI) was calculated. Body composition was assessed by leg-to-leg bioimpedance. Overweight was defined as BMI=25.0-29.9 kg/m(2) and obesity as BMI>or=30.0 kg/m(2). RESULTS: There were highly significant gender and age differences in overweight (YM=0%, YW=10%, OM=6% and OW=34%) and obesity (YM=0%, YW=4%, OM=6% and OW=50%). Only 16% of OW were neither overweight nor obese compared to 88% of OM. OW had a higher fat mass percent (38.4%) than other groups, while fat-free mass (kg) was significantly higher in males than females with YW having the lowest value. Young generations were more educated and more influenced by western ideals than OM and OW. Weight gain was not always associated with weight concern and many overweight/obese subjects did not perceive themselves as overweight. CONCLUSION: Social and behavioural changes are already creating a perceptible 'generational gap' among this population undergoing rapid transition. The improved education and current lean status of the younger adults offers opportunities for preventative interventions. These need to be specially targeted at women.

Adolescent↗
PubMed2006

Body fat reference curves for children.

OBJECTIVE: To refine the diagnosis of childhood obesity by creating new sex-specific centile curves for body fat and to base these references on a simple and affordable method that could be widely adopted in clinical practice and surveys. DESIGN: Body fat was measured by bio-impedance in 1985 Caucasian children aged 5-18 years from schools in Southern England. Smoothed centile charts were derived using the LMS method. RESULTS: The new body fat curves reflect the known differences in the development of adiposity between boys and girls. The curves are similar by sex until puberty but then diverge markedly, with males proportionately decreasing body fat and females continuing to gain. These sex differences are not revealed by existing curves based on body mass index. We present charts in which cutoffs to define regions of 'underfat', 'normal', 'overfat' and 'obese' are set at the 2nd, 85th and 95th centiles. These have been designed to yield similar proportions of overweight/overfat and obese children to the IOTF body mass index cutoffs. CONCLUSIONS: Direct assessment of adiposity, the component of overweight that leads to pathology, represents a significant advance over body mass index. Our new charts will be published by the Child Growth Foundation for clinical monitoring of body fat, along with the software to convert individual measurements to Z-scores.

Adiposity↗
PubMed2005

Early programming of adult diseases in resource poor countries.

Considerable evidence now exists to suggest that early exposure to nutritional deprivation can have long term consequences to health, with low birth weight now considered a risk factor for later health outcomes such as coronary heart disease, stroke, type 2 diabetes, and the metabolic syndrome. Of importance, such effects are most exaggerated when faced with over-nutrition in later life, forming the basis for the "thrifty phenotype" hypothesis. The evidence in support of these associations comes largely from retrospective cohort studies in which adult outcomes were correlated with birth weight records. Relatively little data is available from developing countries, where long term record keeping of birth weight data has not been a high priority. Arguably however, such countries are at the greatest risk from the mismatch of early nutritional deprivation and later nutritional affluence. This paper explores the importance of the "developmental origins of health and disease" hypothesis in resource poor countries.

Adult↗
PubMed2004

An evolutionary model of stature, age at first birth and reproductive success in Gambian women.

We have built a model to predict optimal age at first birth for women in a natural fertility population. The only existing fully evolutionary model, based on Ache hunter-gatherers, argues that as women gain weight, their fertility (rate of giving birth) increases-thus age at first birth represents a trade-off between time allocated to weight gain and greater fertility when mature. We identify the life-history implications of female age at first birth in a Gambian population, using uniquely detailed longitudinal data collected from 1950 to date. We use height rather than weight as an indicator of growth as it is more strongly correlated with age at first birth. Stature does not greatly influence fertility in this population but has a significant effect on offspring mortality. We model age at first reproduction as a trade-off between the time spent growing and reduced infant mortality after maturation. Parameters derived from this population are fitted to show that the predicted optimal mean age of first birth, which maximizes reproductive success, is 18 years, very close to that observed. The reaction norm associated with variation in growth rate during childhood also satisfactorily predicts the variation in age at first birth.

Adolescent↗
PubMed2004

Ethnic differences in the relationship between fasting leptin and BMI in children.

OBJECTIVE: To compare the relationship between fasting serum leptin levels and body mass index (BMI) in children from different ethnic groups. SUBJECTS: Children aged 6-10 y from rural Gambia (n=471) and central Italy (n=839). MEASUREMENTS: Anthropometry (z-score of BMI) and fasting serum leptin concentrations. RESULTS: The Italian children had significantly higher mean BMI z-scores than the Gambian children (males: Italy 1.58, Gambia -1.44, P< or =0.0001; females: Italy 1.33, Gambia -1.42, P< or =0.0001) and significantly higher serum leptin concentrations (males: Italy 8.86 ng ml(-1), Gambia 1.78 ng ml(-1), P< or =0.0001; females: Italy 11.31 ng ml(-1), Gambia 2.22 ng ml(-1), P< or =0.0001). A significantly different relationship was observed between z-score of BMI and serum leptin levels in the Gambian and the Italian children for both boys and girls. CONCLUSION: A different relationship exists between z-score of BMI and leptin levels in these two groups of children from very diverse ethnic backgrounds. Future studies using detailed measures of body composition and energy balance are needed to help understand this relationship.

Body Composition↗
PubMed2003

Leptin does not respond to 48 h fat deposition or mobilization in women.

OBJECTIVE: To test the hypothesis that acute responses of plasma leptin concentration to energy balance manipulation are mediated by fat flux. DESIGN: Ten healthy women aged 31-63 y, mass 48-113.5 kg, fat mass 8.5-62.5 kg, were studied for 3 days in a whole-body calorimeter on two occasions. After a control day (D1) during which energy balance was maintained, diet was manipulated to induce fat deposition (FD) or mobilization (FM) of 50 g/day for 2 days (D2 & D3). A difference totalling of 194+/-18.6 g fat was achieved between manipulations without significant effects on carbohydrate or protein balance. Fasting plasma leptin was measured on D2 and D4. RESULTS: After the control day plasma leptin concentration averaged 19.01+/-9.8 ng/ml, and was found to be linearly related to body fat mass. After 2 days manipulation of fat balance, leptin concentrations were 21.4+/-10.3 ng/ml (FD) and 21.2+/-11.3 ng/ml (FM). There was no significant difference between treatments in either control day or postmanipulation leptin concentrations, nor did the treatments induce any differences in glucose or insulin concentration responses. CONCLUSION: Although in states of energy balance leptin concentration is linearly related to fat mass, acute modulation of leptin concentration during energy imbalance is not mediated by fat flux.

Adipose Tissue↗
PubMed2003

Fast foods, energy density and obesity: a possible mechanistic link.

Fast foods are frequently linked to the epidemic of obesity, but there has been very little scientific appraisal of a possible causal role. Here we review a series of studies demonstrating that the energy density of foods is a key determinant of energy intake. These studies show that humans have a weak innate ability to recognise foods with a high energy density and to appropriately down-regulate the bulk of food eaten in order to maintain energy balance. This induces so called 'passive over-consumption'. Composition data from leading fast food company websites are then used to illustrate that most fast foods have an extremely high energy density. At some typical outlets the average energy density of the entire menus is approximately 1100 kJ 100 g(-1). This is 65% higher than the average British diet (approximately 670 kJ 100 g(-1)) and more than twice the energy density of recommended healthy diets (approximately 525 kJ 100 g(-1)). It is 145% higher than traditional African diets (approximately 450 kJ 100 g(-1)) that probably represent the levels against which human weight regulatory mechanisms have evolved. We conclude that the high energy densities of many fast foods challenge human appetite control systems with conditions for which they were never designed. Among regular consumers they are likely to result in the accidental consumption of excess energy and hence to promote weight gain and obesity.

Appetite Regulation↗
PubMed2003

Impact of nutritional status on antibody responses to different vaccines in undernourished Gambian children.

AIM: To test the efficacy of T-cell-dependent and T-cell-independent vaccines in rural Gambian children suffering from a range of energy/protein and micronutrient deficiencies. METHODS: Nutritional status (anthropometry, haemoglobin, plasma leptin and micronutrient status) and response to two vaccinations (23 valent pneumococcal capsular polysaccharide vaccine, Pneumovax and the Human Diploid-Cell Rabies Vaccine) were assessed in 472 children aged 6 1/2 h to 9 1/2 y. RESULTS: Anthropometry and micronutrient status (as z-scores against European reference values) indicated a range from moderate to severe levels of undernutrition [mean (interquartile range): weight-for-age z-score -1.58 (-2.18 to -0.95); height-for-age z-score -0.94 (-1.51 to -0.35); body-mass-index-for-age z-score -1.43 (-2.05 to -0.84); mid-upper arm circumference -1.41 (-1.72 to -1.13); leptin -1.06 (-1.10 to -1.03); haemoglobin (Hb) -0.30 (-1.18 to 0.79); zinc -1.29 (-2.42 to -0.55); vitamin C -0.01 (-1.18 to 1.15); retinol -1.33 (-1.97 to -0.77)]. A seasonal effect was observed in haemoglobin levels and in all micronutrients (with the exception of zinc and retinol) and in the response to vaccination. After adjusting for seasonality, age and gender, no consistent associations were found between any of the measures of nutritional status and the effectiveness of seroconversion to either of the vaccines. CONCLUSION: The successful short-term seroconversion to whole inactivated viral and bacterial polysaccharide vaccines indicates that the processes leading to antibody secretion remain intact over a wide range of single and combined nutrient deficiencies.

Antibody Formation↗
PubMed2003

Birth season and environmental influences on patterns of thymic growth in rural Gambian infants.

AIM: In rural Gambia, birth season predicts infection-related adult mortality. Seasonal factors in early life may programme the immune system, possibly via an effect on thymic development. This study tested whether thymus size in rural Gambian infants is affected by birth season, defined as January-June (harvest, few infections) versus July-December (hungry, high infectious load). METHODS: Thymic volume (thymic index) was assessed sonographically at 1, 8, 24 and 52 wk in 138 singleton infants born over 14 consecutive months. Growth and morbidity were regularly assessed. RESULTS: Mean thymic index increased from 19.9 at 1 wk to 30.9 at 8 wk and 35.7 at 24 wk, then fell to 32.0 at 52 wk. Thymic index was associated with each preceding thymic index up to 24 wk. This tracking persisted after correcting for infant weight and month of measurement (p < 0.01). Thymic index at 1 wk was marginally but non-significantly lower in hungry season births (p = 0.06). Thymic index was lower in hungry season measurements; this effect persisted after adjusting for current weight and infection markers, and was strongest at 8 wk (p = 0.001). CONCLUSION: These results describe a pattern of thymic growth followed by diminution in size. An infant's thymic index tracks despite changes in body weight and season. Thymic index was lower in the hungry season. This appears not to be explained by infection or nutritional status. A possible influence of trophic factors in breast milk merits investigation.

Body Weight↗
PubMed2002

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 +/-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 (r(2)=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.

Anthropometry↗
PubMed2002

Leptin, malnutrition, and immune response in rural Gambian children.

BACKGROUND: The adipocyte derived hormone, leptin, has cytokine like function and may mediate the effects of starvation on immunity. Mice with congenital leptin deficiency (ob/ob) have small hypocellular thymuses and impaired cellular immunity. In humans leptin influences the differentiation of naïve and memory cells in vitro, and genetic leptin deficiency has been associated with an ill defined susceptibility to infection. AIMS: To describe the in vivo relation of leptin and immune function in children. METHODS: Fasting plasma leptin concentrations, immune function (T and B cell mediated vaccine responses and delayed type hypersensitivity), and mucosal function (dual sugar permeability test and salivary sIgA concentrations) were measured in a cohort of 472 moderately undernourished rural Gambian children. RESULTS: Leptin concentrations correlated with body fat assessed by mid upper arm circumference or BMI for age Z scores, and were very low compared to well nourished European norms (males 1.8 v 11.1 ng/ml; females 2.4 v 13.8 ng/ml). No detectable relations were found between leptin concentrations and any of the measures of immune or mucosal function. CONCLUSIONS: The data confirm that leptin acts as a peripheral signal of energy restriction, but do not support an association between fasting plasma leptin levels and immune function in children of this age.

Antibody Formation↗
PubMed2001

Overeating: the health risks.

Overeating is a relative term. It refers to the consumption of an energy intake that is inappropriately large for a given energy expenditure, thus, leading to obesity. There are several key environmental and cultural factors that have converged in the past few decades to markedly increase the risk of both active and passive (inadvertent) overeating. Chief among these are the increased availability and promotion of cheap energy-dense diets (usually high in fat) and the transition toward extremely sedentary lifestyles. The importance of considering these factors together must be stressed. Data ranging from highly controlled metabolic studies to large-scale epidemiological and ecological analysis illustrate the strong interactions between diet and physical activity in relationship to the over-consumption of energy. Overeating of certain specific dietary components may also lead to health risks. Obvious examples are saturated and trans-fatty acids. More recently attention has switched to high glycemic foods and to n-6 fatty acids. Theories that excess consumption of these may be independent risk factors for obesity and ill health remain controversial but merit closer examination and additional research. The main barriers to changing widely prevalent overeating include the following: public and corporate ignorance about the effects of energy-dense diets in inducing passive over-consumption, commercial willfulness concerning energy density and portion sizes, and public ignorance about the profound health effects of inactive lifestyles. These represent key targets for the design of public health initiatives.

Animals↗
PubMed2001

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 20-140g) in a whole-body indirect calorimeter, and were studied for 8 h. Ingested fat oxidation was estimated from the subject's 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.

Adolescent↗