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Biomedical subjects

S A Jebb

Publications and source records attributed to S A Jebb.

At least 37 records · Page 2Linked to original sources
PubMed2002

Changes in risk factors for cardiovascular disease with body fat loss in obese women.

BACKGROUND: Current guidelines for obesity management emphasize the improvements in health risks associated with weight losses of 5-10% initial weight. However, most of the data is derived from periods of acute weight loss and may not represent the true effect in the longer term or in obese but otherwise healthy individuals. This study examines the temporal changes in risk factors for cardiovascular disease with weight change over 52 weeks. METHODS: In total, 57 overweight women (age 43.7 +/- 9.1 years, mean BMI of 31.7 kg/m2, range 27.2-38.5 kg/m2) with no other significant medical history, entered a milk-based, low-energy weight loss programme for 12 weeks and were then monitored without further intervention until 52 weeks. Weight, fat mass, fasting plasma insulin, lipids and blood pressure were measured at 0, 12, 24 and 52 weeks. RESULTS: The mean weight change in sequential periods was -11.6% (p < 0.0001), +1.1% (p = 0.02) and +5.2% (p < 0.0001). The change from baseline to 1 year being -6.0% (p < 0.0001) an 11% (p < 0.0001) reduction in initial body fat mass. Initial weight loss (0-12 weeks) was positively correlated with greater longer term weight loss (0-52 weeks, r = 0.75, p < 0.0001) and not with weight regain (12-52 weeks, r = 0.14, p = 0.28). Despite significant improvements in insulin sensitivity, lipid profile and blood pressure (BP) with acute weight loss, in the group overall, only benefits in BP were maintained after 52 weeks. However, improvements in insulin sensitivity were sustained in those who maintained more than 5% weight loss, and those with higher baseline metabolic risk had greater benefits with weight loss. Change in waist circumference was better than BMI or fat mass in predicting improvements in metabolic risk in these obese women. CONCLUSIONS: This study suggests, in otherwise apparently healthy obese women, the rationale of targeting individuals most likely to benefit from weight management. Most importantly it highlights the need to focus on achieving initial weight losses of greater than 10% to maintain longer term losses of at least 5% and the associated health benefits.

Adipose Tissue↗
PubMed2001

Partial leptin deficiency and human adiposity.

The adipocyte-derived hormone leptin is crucial for energy homeostasis in mammals; mice and humans without it suffer from a voracious appetite and extreme obesity. The effect on energy balance of variations in plasma leptin above a minimal threshold is uncertain, however, particularly in humans. Here we examine a group of individuals who are genetically partially deficient in leptin, and show that differences in circulating leptin levels within the range found in normal human populations can directly influence the laying down of fat tissue (adiposity).

Adipose Tissue↗
PubMed2001

Beyond body mass index.

Body mass index (BMI) is the cornerstone of the current classification system for obesity and its advantages are widely exploited across disciplines ranging from international surveillance to individual patient assessment. However, like all anthropometric measurements, it is only a surrogate measure of body fatness. Obesity is defined as an excess accumulation of body fat, and it is the amount of this excess fat that correlates with ill-health. We propose therefore that much greater attention should be paid to the development of databases and standards based on the direct measurement of body fat in populations, rather than on surrogate measures. In support of this argument we illustrate a wide range of conditions in which surrogate anthropometric measures (especially BMI) provide misleading information about body fat content. These include: infancy and childhood; ageing; racial differences; athletes; military and civil forces personnel; weight loss with and without exercise; physical training; and special clinical circumstances. We argue that BMI continues to serve well for many purposes, but that the time is now right to initiate a gradual evolution beyond BMI towards standards based on actual measurements of body fat mass.

Adipose Tissue↗
PubMed2000

Overweight and obesity in European children and adolescents.

The conclusions of this mini-workshop are not substantially different from those previously published based on the USA experience [9]. This does not necessarily mean that there are no important differences between Europe and the USA, rather it reflects the paucity of data, especially in Europe. Moreover, European data are dominated by studies in Northern and Western European countries, which are closest in economic terms to the USA. This review has not been able to reflect the position in the less economically advantaged parts of Europe where more substantial differences may occur. Together, these reviews have highlighted the limited and inadequate data available on one of the most important and burgeoning public health problems in the world today. There is an urgent need for more research into the fundamental mechanisms of weight gain and effective interventions if we are to prevent the next generation becoming fatter than their parents.

Adolescent↗
PubMed2000

Evaluation of a new bioelectrical impedance instrument for the prediction of body cell mass independently of height or weight.

The objective of the present study was to evaluate the performance of a new bioelectrical impedance instrument, the Soft Tissue Analyzer (STA), which predicts a subject's body composition. A cross-sectional population study in which the impedance of 205 healthy adult subjects was measured using the STA. Extracellular water (ECW) volume (as a percentage of total body water, TBW) and fat-free mass (FFM) were predicted by both the STA and a compartmental model, and compared according to correlation and limits of agreement analysis, with the equivalent data obtained by independent reference methods of measurement (TBW measured by D(2)O dilution, and FFM measured by dual-energy X-ray absorptiometry). There was a small (2.0 kg) but significant (P < 0.02) difference in mean FFM predicted by the STA, compared with the reference technique in the males, but not in the females (-0.4 kg) or in the combined group (0.8 kg). Both methods were highly correlated. Similarly, small but significant differences for predicted mean ECW volume were observed. The limits of agreement for FFM and ECW were -7.5-9.9 and -4.1-3.0 kg, respectively. Both FFM and ECW (as a percentage of TBW) are well predicted by the STA on a population basis, but the magnitude of the limits of agreement with reference methods may preclude its usefulness for predicting body composition in an individual. In addition, the theoretical basis of an impedance method that does not include a measure of conductor length requires further validation.

Absorptiometry, Photon↗
PubMed2000

Evaluation of the novel Tanita body-fat analyser to measure body composition by comparison with a four-compartment model.

The Tanita body-fat analyser is a novel device to estimate body fat, based on the principles of bioelectrical impedance. It differs from other impedance systems which use surface electrodes in that the subjects stand bare-footed on a metal sole-plate which incorporates the electrodes, hence impedance is measured through the legs and lower trunk. In 104 men and 101 women (16-78 years and BMI 16-41 kg/m2) the mean bias in body-fat mass measured using the Tanita body-fat analyser was 0.8 (2SD 7.9) kg relative to a four-compartment model. This is comparable to the other prediction techniques tested (conventional tetrapolar impedance -1.3 (2SD 6.9) kg, skinfold thicknesses 0.3 (2SD 7.4) kg, and BMI-based formulas -0.2 (2SD 9.0) kg and -0.6 (2SD 8.5) kg), but the agreement was poorer than for 'reference' methods to measure body fat (density 0.2 (2SD 3.7) kg, total body water -0.9 (2SD 3.4) kg and dual-energy X-ray absorptiometry 0.1 (2SD 5.0) kg). The present paper also describes the derivation of a new prediction equation for the calculation of body composition from the Tanita body-fat analyser. The equation incorporates sex, age, and a log-transformation of height, weight and the measured impedance to predict body fat measured by a four-compartment model. This approach is recommended in the derivation of other prediction equations in body composition analysis. Using this novel prediction equation the residual standard deviations were 4.8% for men and 3.3% for women. A similar analysis using data collected with a conventional tetrapolar system yielded residual standard deviations of 4.3% for men and 3.1% for women. This demonstrates that the practical simplicity of the novel Tanita method is not associated with a clinically significant decrement in performance relative to a traditional impedance device.

Absorptiometry, Photon↗
PubMed2000

Methodological approaches to assess body-weight regulation and aetiology of obesity.

Obesity, which is becoming one of the major health hazards in developed and developing societies, results from a long-term positive energy balance. Body-weight regulation and stability depend on an axis with three interrelated components: food intake, energy expenditure and adipogenesis, although there are still many unknown features concerning fuel homeostasis and energy balance. Biochemical processes are interconnected, and a separate consideration of each component is often useful for methodological purposes and to achieve a better understanding of the whole system. Thus, many different experimental approaches can be applied by using laboratory animals, cell culture or human subjects to unravel the molecular mechanisms which participate in body-weight regulation. Thus, both in vitro (cellular and subcellular models) and in vivo methods have dramatically increased our knowledge of weight control. Several strategies in obesity research are reported here, exploiting the opportunities of the molecular era as well as novel whole-body approaches, which will impact on the development of new targets for obesity management and prevention.

Animals↗
PubMed2000

A combined heart rate and movement sensor: proof of concept and preliminary testing study.

OBJECTIVE: Heart rate monitoring has previously been used as a technique for measuring energy expenditure (EE) in field studies. However, the combination of heart rate monitoring with movement sensoring could have theoretical advantages compared to either method used alone. Therefore, this study was undertaken to develop and validate a new combined heart rate monitor and movement sensor instrument (HR+M) for measuring EE. METHODS: The HR+M instrument is a single-piece instrument worn around the chest which records minute-by-minute heart rate and movement. Eight subjects underwent an individual calibration in which EE and heart rate were measured at rest and during a sub-maximal bicycle ergometer test. They then wore the HR+M for 24 hours in a whole-body calorimeter and underwent a standard protocol including periods of physical activity and inactivity. Minute-by-minute heart rate was converted to EE using individual calibration curves with the motion data discriminating between periods of inactivity and activity at low heart rate levels. EE was also calculated using the HRFlex method which relies on heart rate alone. Both estimates of EE were compared to EE measured in the whole-body calorimeter. RESULTS: The mean percentage error of the HR+M method calculating TEE compared with the gold standard of the calorimeter measurement was 0.00% (95% CI of the mean error -0.25, 1. 25). The HRFlex method using the heart rate information alone resulted in a mean percentage error of 16.5% (95% CI of the mean error -0.57, 1.76). CONCLUSIONS: This preliminary test of HR+M demonstrates its ability to estimate EE and the pattern of EE and activity throughout the day. Further validation studies in free-living individuals are necessary. SPONSORSHIP: NJW is an MRC Clinician Scientist Fellow. KLR holds an MRC PhD scholarship.

Adult↗
PubMed2000

Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index.

BACKGROUND: Although international interest in classifying subject health status according to adiposity is increasing, no accepted published ranges of percentage body fat currently exist. Empirically identified limits, population percentiles, and z scores have all been suggested as means of setting percentage body fat guidelines, although each has major limitations. OBJECTIVE: The aim of this study was to examine a potential new approach for developing percentage body fat ranges. The approach taken was to link healthy body mass index (BMI; in kg/m(2)) guidelines established by the National Institutes of Health and the World Health Organization with predicted percentage body fat. DESIGN: Body fat was measured in subjects from 3 ethnic groups (white, African American, and Asian) who were screened and evaluated at 3 universities [Cambridge (United Kingdom), Columbia (United States), and Jikei (Japan)] with use of reference body-composition methods [4-compartment model (4C) at 2 laboratories and dual-energy X-ray absorptiometry (DXA) at all 3 laboratories]. Percentage body fat prediction equations were developed based on BMI and other independent variables. RESULTS: A convenient sample of 1626 adults with BMIs < or =35 was evaluated. Independent percentage body fat predictor variables in multiple regression models included 1/BMI, sex, age, and ethnic group (R: values from 0.74 to 0.92 and SEEs from 2.8 to 5.4% fat). The prediction formulas were then used to prepare provisional healthy percentage body fat ranges based on published BMI limits for underweight (<18.5), overweight (> or =25), and obesity (> or =30). CONCLUSION: This proposed approach and initial findings provide the groundwork and stimulus for establishing international healthy body fat ranges.

Absorptiometry, Photon↗
PubMed2000

Dominant and recessive inheritance of morbid obesity associated with melanocortin 4 receptor deficiency.

Over 20 severely obese subjects in 11 independent kindreds have been reported to have pathogenic heterozygous mutations in the gene encoding the melanocortin 4 receptor (MC4R), making this the most common known monogenic cause of human obesity. To date, the detailed clinical phenotype of this dominantly inherited disorder has not been defined, and no homozygous subjects have been described. We determined the nucleotide sequence of the entire coding region of the MC4R gene in 243 subjects with severe, early-onset obesity. A novel two-base pair GT insertion in codon 279 was found in two unrelated subjects, and four novel missense mutations, N62S, R165Q, V253I, C271Y, and one mutation (T112M) reported previously were found in five subjects. N62S was found in homozygous form in five children with severe obesity from a consanguineous pedigree. All four heterozygous carriers were nonobese. Several features of the phenotype, e.g. hyperphagia, tendency toward tall stature, hyperinsulinemia, and preserved reproductive function, closely resemble those reported previously in Mc4r knock-out mice. In addition, a marked increase in bone mineral density was seen in all affected subjects. In transient transfection assays, the N62S mutant receptor showed a responsiveness to alphaMSH that was intermediate between the wild-type receptor and mutant receptors carrying nonsense and missense mutations associated with dominantly inherited obesity. Thus MC4R mutations result in a syndrome of hyperphagic obesity in humans that can present with either dominant or recessive patterns of inheritance.

Adolescent↗
PubMed1999

The Nutrition Society Medical Lecture. Obesity: from molecules to man.

Obesity is now a major public health problem in both developed and developing countries. In the UK over 16% men and 17.5% women are obese, an increase of more than 100% since 1980. However, interventions to prevent and treat obesity are hampered by an inadequate understanding of the aetiology of this condition. The present paper considers the current state of knowledge regarding the causes of obesity, including some of the genetic, metabolic, behavioural and environmental factors which influence energy balance. The present paper comprises The Nutrition Society Medal Lecture and focuses in particular on the research carried out at the MRC Dunn Nutrition Centre in Cambridge. It argues that despite decades of intensive research there is relatively little evidence of genetic or metabolic defects to explain the majority of cases of human obesity. Instead we must look to behavioural and/or environmental factors which may be underpinning the current epidemic of obesity.

Diet↗
PubMed1999

Contribution of a sedentary lifestyle and inactivity to the etiology of overweight and obesity: current evidence and research issues.

PURPOSE: The etiology of overweight and obesity is clearly multifactorial, but ultimately it is determined by the long-term balance between energy intake and expenditure. This review will consider the effects on body weight and the risk of obesity of sedentary lifestyles, within the context of dietary habits. METHODS: The data from ecological, cross-sectional, and prospective studies that have assessed physical activity and dietary intake and their relationship to body weight were reviewed. RESULTS: Ecological analyses imply that the increase in the prevalence of obesity is more strongly related to lower levels of physical activity than higher energy intakes. However, there is a paucity of pertinent data from cross-sectional or prospective studies. There is some evidence that both a high proportion of dietary fat and low levels of physical activity may increase the likelihood of weight gain. However, even the most comprehensive studies are unable to account for more than a small proportion of the interindividual variance in weight gain, so it is difficult to usefully assess their relative importance. Furthermore, there are insufficient data that pertain to "sedentary lifestyles" to segregate any putative effect from a protective effect of exercise. All the data in this review is NHLBI Evidence category C. CONCLUSIONS: This review provides clear evidence that low levels of physical activity are associated with an increased risk of weight gain and obesity. On balance, the evidence is suggestive of a causal link, but the experimental designs are too weak is provide conclusive evidence. The potential effect of interactions between diet and activity have largely been ignored. To make progress in this area, a number of key issues need to be resolved with regard to the methodology, study design, and statistical analysis of prospective epidemiological studies. In the meantime, data need to be drawn from other sources, particularly those studies designed to elucidate the mechanism of action of diet and physical activity in the etiology of obesity, to establish rational interventions to guide public health policies.

Cross-Sectional Studies↗
PubMed1998

Leptin: physiology and pathophysiology.

The identification and sequencing of the ob gene and its product, leptin, in late 1994 opened new insights in the study of the mechanisms controlling body weight and led to a surge of research activity. During this time, a considerable body of knowledge regarding leptin's actions has been accumulated and the field continues to expand rapidly. Currently there is particular interest in the interaction of leptin with other peripheral and neural mechanisms to regulate body weight, reproduction and immunological response. In this review, we attempt to place the current state of knowledge about leptin in the broader perspective of physiology, including its structural characteristics, receptors, binding proteins, signalling pathways, regulation of adipose tissue expression and production, secretion patterns, clearance mechanisms and functional effects. In addition, leptin's involvement in the pathophysiology of obesity, anorexia nervosa, diabetes mellitus, polycystic ovary syndrome, acquired immunodeficiency syndrome, cancer, nephropathy, thyroid disease, Cushing's syndrome and growth hormone deficiency will be reviewed.

Animals↗
PubMed1997

Longitudinal changes in body composition measured with a variety of methods in patients with AIDS.

We test the hypothesis that human immunodeficiency virus (HIV)-related weight loss is accompanied by inappropriately large losses of fat-free mass (FFM). Our secondary aims were to examine whether FFM increases during weight gain and to compare several techniques for measuring FFM change. FFM was measured at intervals averaging 5 months in 21 AIDS patients by means of skinfold thickness (SF), dual-energy x-ray absorptiometry (DEXA), total body water (TBW), and bioelectrical impedance using the equation of the manufacturer of the equipment (BIA(EZComp)) and a published prediction equation (BIA(Segal)). The FFM content of weight loss was similar for SF (57%), DEXA (60%), TBW (55%) and BIA(EZComp) (65%), but the result from BIA(Segal) (78%) was higher. The results were close to predicted starvation values apart from the results with BIA(Segal), which were significantly higher than predicted values. Weight gain was also composed of a large proportion of FFM. There were large intermethod differences in measurements of absolute FFM, but for measuring changes in FFM, the bias between SF, DEXA, and TBW was minimal. The results of BIA vary with the prediction equation used. In this group of patients with the acquired immune deficiency syndrome (AIDS), weight loss was composed of a large proportion of FFM, but in general this is compatible with undernutrition as the underlying cause and does not support the hypothesis of excessive FFM catabolism in HIV disease. SF, DEXA, TBW, and BIA(Segal) show reasonable agreement for measuring body composition changes. This information should be considered in the design of future intervention studies for HIV-related wasting.

Absorptiometry, Photon↗
PubMed1997

Total energy expenditure in patients with small-cell lung cancer: results of a validated study using the bicarbonate-urea method.

The bicarbonate-urea method for measuring CO2 production was applied to eight free-living patients (mean age, 68 +/- 10 years; mean weight, 69 +/- 10 kg; mean height, 1.65 +/- 0.10 m) with unresectable small-cell lung cancer for a period of 1 day (n = 5) or 2 days (n = 3). The basal metabolic rate (BMR) was measured in all subjects. The technique was first validated against whole-body indirect calorimetry over an additional 24-hour period in five of these subjects. The bicarbonate-urea method predicted net CO2 production to be 102.1% +/- 3.4% of that measured by whole-body indirect calorimetry, and energy expenditure, 101.5% +/- 3.8% of the measured calorimeter value (8.1 +/- 1.6 MJ/d). The 24-hour recovery of label in CO2 excreted by the body was 95.6% +/- 0.5%. In free-living conditions, the bicarbonate-urea method predicted energy expenditure to be 9.0 +/- 2.6 MJ/d. BMR was elevated by a mean of 6% (P < .05) compared with the Schofield standards. The physical activity level ([PAL] the ratio of total energy expenditure [TEE] to BMR) was variable (1.15 to 1.87), but the mean value was only 1.36 +/- 0.22, considerably less than that of moderately active healthy subjects with estimated PAL values of 1.55 (P < .05) to 1.65 (P < .01) and the mean results obtained by doubly labeled water (previous studies) in healthy age- and sex-matched subjects. This is the first time a tracer method for measuring CO2 production and energy expenditure has been validated against whole-body 24-hour indirect calorimetry in patients with lung cancer or a systemic inflammatory reaction. The agreement between the two methods is similar to that observed in normal subjects. This is also the first time a tracer method has been used to measure energy expenditure in free-living patients with lung cancer. The results suggest that TEE and the energy requirements necessary to maintain energy balance were not increased despite basal hypermetabolism, because of the associated decrease in physical activity.

Adult↗