Energy expenditure at rest and during sleep in children with Prader-Willi syndrome is explained by body composition

BACKGROUND: Obesity in Prader-Willi syndrome (PWS) seems to be related to a low basal metabolic rate (BMR). In addition, abnormal sleep patterns reported in PWS might affect sleeping metabolic rate (SMR). OBJECTIVE: Our objective was to assess BMR and SMR adjusted for fat-free mass in young PWS patients. DESIGN: Subjects were 17 PWS patients (10 females and 7 males aged 7.5-19.8 y) and 17 obese control subjects matched for sex and bone age. SMR was measured in a respiratory chamber, BMR with a ventilated-hood system, and body composition by deuterium dilution. RESULTS: BMR and SMR were significantly lower in the PWS group than in the control group (5.36 +/- 1.18 and 4.62 +/- 1.08 MJ/d compared with 6.38 +/- 1.55 and 5.60 +/- 1.52 MJ/d, respectively; P < 0.05). When fat-free mass was included in the analysis, multiple regression showed no differences in BMR and SMR between groups. When weight was included in the analysis instead of fat-free mass, SMR was lower in the PWS group. Fat-free mass was lower in the PWS group both as an absolute value and when adjusted for height. CONCLUSION: BMR and SMR are low in young patients with PWS because of a low fat-free mass.     

Effects of familial predisposition to obesity on energy expenditure in multiethnic prepubertal girls

BACKGROUND: The prevalence of childhood obesity is increasing and the causes of this are unknown. OBJECTIVE: The objective of this study was to determine whether energy expenditure (EE), measured by 24-h calorimetry and doubly labeled water, differed in normal-weight-for-height, multiethnic prepubertal girls with or without a familial predisposition to obesity. DESIGN: Normal-weight, prepubertal white (n = 52), African American (n = 30), and Hispanic (n = 19) girls with a mean (+/-SD) age of 8.5 +/- 0.4 y were studied according to parental leanness and overweight or obesity. The girls were grouped according to whether they had 2 lean parents (n = 30), 2 obese parents (n = 27), or 1 lean and 1 obese parent (n = 44). Basal metabolic rate (BMR), sleeping metabolic rate (SMR), 24-h EE, respiratory quotient, heart rate, and activity were measured by 24-h room calorimetry; free-living total EE (TEE), activity-related EE (AEE), and physical activity level were measured by doubly labeled water. EE was standardized by fat-free mass (FFM). RESULTS: There were no significant differences among familial groups in weight, height, fat mass, FFM, or percentage body fat. African American girls had a higher FFM than did white or Hispanic girls (P < 0.05). BMR, SMR, 24-h EE, respiratory quotient, heart rate, and activity levels were not significantly different among familial groups. Additionally, there were no significant familial group differences in TEE, AEE, or physical activity level. However, BMR, SMR, and TEE were lower in African American girls than in white girls (P < 0.05). CONCLUSION: There was no significant difference in EE between normal-weight, multiethnic prepubertal girls predisposed to obesity and those not predisposed to obesity.     

The difference between the basal metabolic rate and the sleeping metabolic rate in Japanese

Previous studies have demonstrated the difference between the basal metabolic rate (BMR) and the sleeping metabolic rate (SMR): however, the difference in the Japanese population has not yet been explored. This study examined the relationship between the BMR and SMR in ninety-four healthy Japanese subjects (37 males and 57 females, 39 +/- 12 y of age and 22.0 +/- 7.4% body fat) in a respiratory chamber. The SMR was significantly lower than the BMR (1416 +/- 245 vs. 1492 +/- 256 kcal/d): however, there was a highly significant correlation between the two (r = 0.867; p < 0.001). The ratio of SMR/BMR largely varied among individuals (0.95 +/-0.08, 8.4% of the coefficient of variation). The ratio was significantly lower in males than in females (0.93 +/- 0.10 vs. 0.97 +/- 0.06, p < 0.05). None of the anthropometric measures (age, weight, body mass index, body surface area or percent body fat) correlated with the ratio. These results showed that SMR was 95%, of BMR on average in a healthy Japanese group. However, when applied over a longer time period (24 h or more), the difference tends to become negligible for most analyses in a group. Although the difference between SMR and BMR will induce a 5% gap of physical activity level defined as the total energy expenditure divided by the BMR or SMR, this factor seems to have little practical importance in epidemiological research.     

Metabolic rate and substrate oxidation of young males with obesity at the different sleep stages

ObjectiveInsufficient and poor-quality sleep among young adults is closely related to obesity and may impact metabolic processes. The mobilization and use of endogenous substrates during sleep, especially fat oxidation, is essential for energy metabolism. This study investigated whether there are differences in sleep structure, metabolic rate, substrate oxidation, and the respiratory quotient (RQ) between young males with normal weight and obesity according to sleep stages and overnight sleep.MethodsFifteen young males with normal weight and fifteen with obesity posited electrodes of polysomnography (PSG) and slept in the metabolic chamber for estimation of sleep structure, sleep metabolic rate (SMR), carbohydrate oxidation (CHOO), fat oxidation (FATO), and RQ. Fat-free mass (FFM) was measured by bioelectrical impedance analysis.ResultsThe sleep period time (p = 0.038) and total sleep time (p = 0.032) were significantly shorter in the obesity group than in the normal-weight group. The obesity group also had a longer sleep latency (p = 0.034) and more sleep-turning events (p = 0.018). CHOO/FFM and the RQ were higher in the obesity group while FATO/FFM was significantly higher in the normal-weight group. FATO/FFM was also higher in the normal-weight group in each sleep stage whereas the RQ was higher in the obesity group (p < 0.05).ConclusionsYoung males with obesity showed lower fat oxidation and more dominant carbohydrate-derived fuel oxidation than normal-weight during sleep and experienced shorter sleep periods and total sleep time.     

Aging and energy expenditure

Whether sedentary energy expenditure is normal or lower in elderly people has not yet been clearly established. Twenty-four-hour energy expenditure (24EE) and its different components were measured by use of a respiratory chamber in elderly (17 male, 21 female; 71 +/- 6 y, mean +/- SD; 71.2 +/- 13.5 kg; 32 +/- 8% fat) and young (33 male, 31 female; 24 +/- 4 y; 84.5 +/- 23.1 kg; 25 +/- 13% fat) subjects. The elderly subjects had lower mean height (P less than 0.001), weight (P less than 0.01), and fat-free mass (P less than 0.001) but higher percent body fat (P less than 0.01) than did the young adults. Absolute 24EE, basal metabolic rate (BMR), and sleeping metabolic rate were significantly lower (P less than 0.01) in the elderly subjects than in the young subjects. However, after differences in fat-free mass, fat mass, and sex were adjusted for, only BMR was found to be lower in the elderly subjects (P less than 0.01). Despite a reduced adjusted BMR in older subjects, sedentary 24EE was decreased only in proportion to their reduced body size, suggesting that the lower energy intake reported in elderly people might be mainly related to lower physical activity in free-living conditions.     

Energy metabolism in African Americans: potential risk factors for obesity.

BACKGROUND: Recent reports have identified a lower resting metabolic rate in African Americans than in whites, but most studies included only females and used short-term measurements with ventilated-hood systems. OBJECTIVE: Our objective was to compare 24-h measurements of energy metabolism between African American and white women and men using a respiratory chamber. DESIGN: Thirty-eight African American (x +/- SD: 32 +/- 7 y of age, 24 +/- 10% body fat) and 288 white (31 +/- 7 y of age, 26 +/- 12% body fat) subjects spent 24 h in a respiratory chamber for measurement of 24-h energy expenditure (24EE), sleeping metabolic rate (SMR), 24-h respiratory quotient (24RQ), and substrate oxidation rates. RESULTS: After adjustment for sex, age, and body composition (by hydrodensitometry), African Americans had lower SMR (-301 +/- 105 kJ/d; P < 0.01) and higher 24RQ (0.014 +/- 0.004; P < 0.001) than whites, whereas 24EE was similar. A sex-specific analysis, using a subset of 38 whites with an equal sex distribution and similar age and body weight, revealed that African American women had lower SMR (-442 +/- 182 kJ/d; P < 0.05) and lower 24EE (-580 +/- 232 kJ/d; P < 0.05), but similar 24RQ values compared with white women. African American men tended to have lower SMRs than white men (-355 +/- 188 kJ/d; P = 0. 07), but had higher 24RQ values, accounting for a 992 +/- 327-kJ/d lower 24-h fat oxidation rate (P < 0.005). CONCLUSIONS: These data not only confirm the findings of a lower metabolic rate in African American than in white women, but also suggest that fat oxidation is lower in African American men than in white men.     

Interindividual variability in sleeping metabolic rate in Japanese subjects

INTRODUCTION: Basal metabolic rate (BMR) or sleeping metabolic rate (SMR) is the largest component of total energy expenditure (EE). An accurate prediction of BMR or SMR is needed to accurately predict total EE or physical activity EE for each individual. However, large variability in BMR and SMR has been reported. OBJECTIVES: This study was designed to develop prediction equations using body size measurements for the estimation of both SMR and BMR and to compare the prediction errors with those in previous reports. METHODS: We measured body size, height, weight and body composition (fat mass and fat-free mass) from skinfold thickness in adult Japanese men (n=71) and women (n=66). SMR was determined as the sum of EE during 8 h of sleep (SMR-8h) and minimum EE during 3 consecutive hours of sleep (SMR-3h) measured using two open-circuit indirect human calorimeters. BMR was determined using a human calorimeter or a mask and Douglas bag. RESULTS: The study population ranged widely in age. The SMR/BMR ratio was 1.01+/-0.09 (range 0.82-1.42) for SMR-8h and 0.94+/-0.07 (range 0.77-1.23) for SMR-3h. The prediction equations for SMR accounted for a 3-5% larger variance with 2-3% smaller standard error of estimate (SEE) than the prediction equations for BMR. DISCUSSION: SMR can be predicted more accurately than previously reported, which indicates that SMR interindividual variability is smaller than expected, at least for Japanese subjects. The prediction equations for SMR are preferable to those for BMR because the former exhibits a smaller prediction error than the latter.     

Comprehensive assessment of the components of energy expenditure in infants using a new infant respiratory chamber.

BACKGROUND: Current methods for energy expenditure (EE) measurements in term infants do not include simultaneous measurements of basal and sleeping metabolic rates (BMR and SMR) or a measure of physical activity (PA). Furthermore, prediction equations for calculating EE are not appropriate for use in infants with metabolic disorders. OBJECTIVE: To develop and utilize a new infant respiratory chamber for simultaneous measurements of EE (kJ/d), preprandial BMR (kJ/d), SMR (kJ/d) and an index of PA (oscillations/min/kg body weight) in infants with a variety of metabolic disorders, for up to four hours in a hospital setting, while allowing parental interaction in a comfortable environment. METHODS: We obtained simultaneous measurements of EE, BMR, SMR and PA in 21 infants (66+/-73 days of age, 4.5+/-1.7 kg body weight, 55+/-8 cm in length and 16+/-7% body fat) using our new infant respiratory chamber. Six of these infants were healthy, seven had thyroid dysfunction, five were HIV-exposed, one had AIDS, one had intrauterine and postnatal growth retardation and one was a hypothermic preterm infant. Energy expenditure, BMR and SMR were extrapolated for 24 hours. Body composition was estimated by skin-fold thickness, using age-appropriate formulae. Basal metabolic rate obtained with the infant respiratory chamber was compared to BMR that was calculated using the appropriate World Health Organization (WHO) equations. RESULTS: In all infants both extrapolated 24-hour EE and BMR correlated with fat-free mass (r = 0.89, p<0.01 and r = 0.88, p<0.01 respectively). Twenty-four hour EE also correlated with PA (r = 0.52, p<0.05). The HIV-exposed infants had higher BMR (p<0.05) than that calculated by the appropriate WHO equation. We found that the caloric requirements for the infant with growth retardation were underestimated based on the infant's weight and age. CONCLUSIONS: The infant respiratory chamber can measure all of the main components of EE. Some of the results obtained differed significantly from those obtained by the WHO equations; therefore, the new infant respiratory chamber is necessary for estimating EE in infants with metabolic and growth disorders.     

Low plasma leptin concentration and low rates of fat oxidation in weight-stable post-obese subjects

OBJECTIVE: A low resting metabolic rate for a given body size and composition, a low rate of fat oxidation, low levels of physical activity, and low plasma leptin concentrations are all risk factors for body weight gain. The aim of the present investigation was to compare resting metabolic rate (RMR), respiratory quotient (RQ), levels of physical activity, and plasma leptin concentrations in eight post-obese adults (2 males and 6 females; 48.9 +/- 12.2 years; body mass index [BMI]: 24.5 +/- 1.0 kg/m2; body fat 33 +/- 5%; mean +/- SD) who lost 27.1 +/- 21.3 kg (16 to 79 kg) and had maintained this weight loss for > or =2 months (2 to 9 months) to eight age- and BMI-matched control never-obese subjects (1 male and 7 females; 49.1 +/- 5.2 years; BMI 24.4 +/- 1.0 kg/m2; body fat 33 +/- 7%). RESEARCH METHODS AND PROCEDURES: Following 3 days of weight maintenance diet (50% carbohydrate and 30% fat), RMR and RQ were measured after a 10-hour fast using indirect calorimetry and plasma leptin concentrations were measured using radioimmunoassay. Levels of physical activity were estimated using an accelerometer over a 48-hour period in free living conditions. RESULTS: After adjustment for fat mass and fat-free mass, post-obese subjects had, compared with controls, similar levels of physical activity (4185 +/- 205 vs. 4295 +/- 204 counts) and similar RMR (1383 +/- 268 vs. 1430 +/- 104 kcal/day) but higher RQ (0.86 +/- 0.04 vs. 0.81 +/- 0.03, p < 0.05). Leptin concentration correlated positively with percent body fat (r = 0.57, p < 0.05) and, after adjusting for fat mass and fat-free mass, was lower in post-obese than in control subjects (4.5 +/- 2.1 vs. 11.6 +/- 7.9 ng/mL, p < 0.05). DISCUSSION: The low fat oxidation and low plasma leptin concentrations observed in post-obese individuals may, in part, explain their propensity to relapse.     

Obese Japanese adults with type 2 diabetes have higher basal metabolic rates than non-diabetic adults

Several cross-sectional studies in Pima Indians and Caucasians have indicated that obese individuals with type 2 diabetes have a higher basal metabolic rate (BMR) than healthy, obese individuals. However, no study has investigated this comparison in Japanese subjects, who are known to be susceptible to type 2 diabetes due to genetic characteristics. Thirty obese Japanese adults with pre-type 2 diabetes (n=7) or type 2 diabetes (n=13) or without diabetes (n=10) participated in this study. BMR was measured using indirect calorimetry. The relationships between residual BMR (calculated as measured BMR minus BMR adjusted for fat-free mass, fat mass, age, and sex) and biomarkers including fasting glucose, glycosylated hemoglobin (HbA(1c)), fasting insulin, homeostasis model assessment of insulin resistance (HOMA-R), triglycerides, and free fatty acids were examined using Pearson's correlation. BMR in diabetic subjects adjusted for fat-free mass, fat mass, age, and sex was 7.1% higher than in non-diabetic subjects. BMR in diabetic subjects was also significantly (p<0.05) higher than in non-diabetic subjects. There was a significant correlation between residual BMR and fasting glucose (r=0.391, p=0.032). These results indicate that in the Japanese population, obese subjects with type 2 diabetes have higher BMR compared with obese non-diabetic subjects. The fasting glucose level may contribute to these differences.     

医学生在校3年体质量和体脂及体型的变化

目的 了解医学生在校期间体质量、体脂和体型的变化,为管理体质量促进健康提供科学依据。方法 跟踪100名医学生(男生44名,女生56名),分别于大学二年级和五年级下学期初,测量体质量、身高、腰围、体脂肪量、去脂量和体脂率。结果 3年间男生体质量、体质指数、腰围、体脂量、去脂量、体脂率分别增加4.46 kg、1.35 kg/m2、4.33 cm、2.48 kg、1.98 kg,2.57%, 而女生腰围增加0.78 cm,去脂量减少0.8 kg。男生79.5%体质量增加,平均增加5.9 kg;女生仅46.4%体质量增加,平均增加3.25 kg,女生41.1%体质量降低,平均降低2.73 kg。3年间男生体型构成比发生明显变化(P<0.05),中心型肥胖前期率和中心型肥胖率分别增加18.2%和4.5% 。腰围变化与体质量变化、体脂率变化呈显著正相关(P<0.01)。结论 医学生在校后期,男生体质量和中心型肥胖明显增加,是体质量管理的重点对象。     

Energy metabolism and requirements in different ethnic groups

Some studies on energy metabolism of men and women in Third World countries suggested that their basal metabolic rate (BMR) is lower compared to BMRs of people in Northern European and American countries. It is, however, not clear whether this results from ethnic factors, climate or adaptation to, for instance, a low energy intake. A study on energy requirements of people from Third World countries has therefore been performed. People with different ethnic backgrounds participated; they were divided into four ethnic groups: 8 African males, 7 Asian males of Mongolian origin (Asian-M), 8 Asian males of Caucasian origin (Asian-C) and 7 European males, who formed the control group. The participants from outside Europe had spent at least 3 months in the Netherlands. All participants consumed a diet (12 per cent of energy from protein, 22 per cent from fat and 66 per cent from carbohydrate) during 8 d. The dietary energy given to each individual was estimated to maintain energy equilibrium during the experiment. The last 3 nights and 2 days were spent in an indirect whole-body calorimeter. Two 24-h energy expenditure (24hEE) measurements were performed on each subject. The environmental temperature inside the calorimeter was 22.0-24.5 degrees C. Physical activity was light, mainly sedentary, with 75 min bicycling at 15 W. The Asian subjects had a significantly lower body weight and fat-free mass than the Europeans. Energy requirement (ER), 24hEE and EE during the night (8 h sleep) was lower in the Asian and African subjects compared to the Europeans, but the difference only reached significance for the Asian-C and African males. When ER, 24hEE and EE-night were expressed in relation to body weight and fat-free mass the Asian groups showed a higher ER and higher EE than the Europeans. This result is contrary to findings of others and may be caused eg, by a higher body weight and fat-free mass of the European controls. Comparison of EE-night with BMR estimated from FAO/WHO/UNU equations showed that the EE-night was consistently lower by about 9 per cent. This suggests that EE during the night may not be predicted by the BMR estimated by widely used equations. This study does not give conclusive evidence that an ethnic factor is involved in energy metabolism in humans.     

Resting energy expenditure and substrate utilisation rate in children with constitutional leanness or obesity

BACKGROUND & AIM: The influence of energy expenditure on body weight regulation, in the absence of organic disease, has never been studied in a paediatric population covering a broad range of body weights. The aim of this study was to investigate resting energy metabolism in children with constitutional leanness, normal body weight, or common obesity. METHODS: Fourteen children with constitutional leanness, 16 children with obesity, and controls were studied. Resting energy expenditure and postabsorptive substrate utilisation rate were measured by indirect calorimetry and body composition was assessed from skinfold thicknesses. RESULTS: As compared to the predicted value calculated from the regression equation of resting energy expenditure on fat-free mass in the controls, resting energy expenditure was decreased in lean children (P=0.002), whereas no difference was found in obese children. In obese children and the overall population, fat mass was positively correlated with fat oxidation rate. In each group and in the overall population, fat oxidation rate was positively correlated to resting energy expenditure. CONCLUSIONS: Constitutionally lean children have a low resting metabolic rate, probably adaptive in nature. In obese children, resting energy expenditure is increased in proportion to the fat-free mass, and fat balance is the main determinant of energy balance. These data suggest a constitutional regulation of body weight.     

Relationship between birth weight and body composition, energy metabolism, and sympathetic nervous system activity later in life

OBJECTIVE: Epidemiological studies suggest that high birth weight might be associated with an increased risk of obesity later in life. Programming of metabolic, endocrine, and/or autonomic pathways during intrauterine development has been proposed to explain this association. RESEARCH METHODS AND PROCEDURES: To determine the relationship between birth weight and body composition and energy metabolism later in life, we measured fat mass and fat-free mass (hydrodensitometry or double-energy X-ray absorptiometry), 24-hour energy expenditure, sleeping metabolic rate, and 24-hour respiratory quotient (respiratory chamber) in 272 adult nondiabetic Pima Indians (161 males/ 111 females, age 25 +/- 5 years, mean +/- SD). In these subjects, birth weight varied over a wide range (2,000 to 5,000 g). Individuals known to be offspring of diabetic pregnancies were excluded. In 44 of the 272 subjects, muscle sympathetic nerve activity was assessed by microneurography. RESULTS: Birth weight was positively correlated with adult height (r = 0.20, p < 0.001) and fat-free mass (r = 0.21, p < 0.001), but not with fat mass (r = 0.01, not significant). Sleeping metabolic rate, adjusted for age, sex, fat-free mass, and fat mass, was negatively related to birth weight (r = -0.13, p < 0.05), whereas adjusted 24-hour energy expenditure (r = 0.07, not significant) and 24-hour respiratory quotient (r = -0.09, not significant) were not. There was no relationship between birth weight and muscle sympathetic nerve activity (r = 0.12, not significant, n = 44). DISCUSSION: In Pima Indians who are not offspring of diabetic pregnancies, high birth weight is associated with increased height and lean body mass, but not with increased adiposity later in life. Although high birth weight may be associated with relatively low resting energy expenditure, it is not associated with major abnormalities in 24-hour energy metabolism or with low muscle sympathetic nerve activity later in life.     

Additional anthropometric measures may improve the predictability of basal metabolic rate in adult subjects

BACKGROUND: The most commonly used predictive equation for basal metabolic rate (BMR) is the Schofield equation, which only uses information on body weight, age and sex to derive the prediction. However, because body composition is a key influencing factor, there will be error in calculating an individual's basal requirements based on this prediction. OBJECTIVE: To investigate whether adding additional anthropometric measures to the standard measures can enhance the predictability of BMR and to cross-validate this within a separate subgroup. DESIGN: Cross-sectional study of 150 Caucasian adults from Scotland, with a body mass index range of 16.7-49.3 kg/m(2). All subjects underwent measurement of BMR, body composition, and 148 also had basic skinfold and circumference measures taken. The resultant equation was tested in a subgroup of 39 obese males. RESULTS: The average difference between the predicted (Schofield equation) and measured BMR was 502 kJ/day. There was a slight systematic bias in this error, with the Schofield equation underestimating the lowest values. The average discrepancy between predicted and actual BMR was reduced to 452 kJ/day, with the addition of fat mass, fat-free mass, an overall 10% improvement on the Schofield equation (P=0.054). Using an equation derived from principal components analysis of anthropometry measurements similarly decreased the difference to 458 kJ/day (P=0.039). Testing the equation in a separate group indicated a 33% improvement in predictability of BMR, compared to the Schofield equation. CONCLUSIONS: In the absence of detailed information on body composition, utilizing anthropometric data provides a useful alternative methodology to improve the predictability of BMR beyond that achieved from the standard Schofield prediction equation. This should be confirmed in more individuals, both within the obese and normal weight category.     

Plasma concentrations of free triiodothyronine predict weight change in euthyroid persons

BACKGROUND: Factors that influence energy metabolism and substrate oxidation, such as thyroid hormones (THs), may be important regulators of body weight. OBJECTIVE: We investigated associations of THs cross-sectionally with obesity, energy expenditure, and substrate oxidation and prospectively with weight change. DESIGN: Euthyroid, nondiabetic, healthy, adult Pima Indians (n = 89; 47 M, 42 F) were studied. Percentage body fat (%BF) was measured by using dual-energy X-ray absorptiometry; sleeping metabolic rate (SMR), respiratory quotient, and substrate oxidation rates were measured in a respiratory chamber. Thyroid-stimulating hormone (TSH), free thyroxine (T(4)), free triiodothyronine (T(3)), and leptin concentrations were measured in fasting plasma samples. RESULTS: TSH, but neither free T(3) nor free T(4), was associated with %BF and leptin concentrations (r = 0.27 and 0.29, respectively; both: P 相似文献   

Sleeping metabolic rate in relation to body composition and the menstrual cycle.

The relationship between sleeping metabolic rate (SMR) measured from 0300 to 0600 h in a respiration chamber and body composition was studied in 47 healthy adult subjects (23 men and 24 women). The effect of the menstrual cycle on SMR was examined in 16 of the 24 women. SMR increased in the postovulation phase of the menstrual cycle (estimated as days 18-29 after last menstruation) 7.7% on average (P less than 0.001). A stepwise regression showed that both fat-free mass (FFM), fat mass (FM), and the phase of the menstrual cycle contributed significantly to SMR. After adjustment for FFM and FM, no sex differences in SMR (men vs preovulation women) remained. The inclusion of FM in this model is an improvement that eliminates the sex difference in SMR/FFM that is usually found. A prediction equation is given that explains 85% of the variance in SMR among individuals.     

Limitations and validation of bioelectrical impedance analysis in morbidly obese patients

PURPOSE OF REVIEW: Several factors limit the use of bioelectrical impedance analysis as a valid predictor of the amount of body fat in morbidly obese individuals. The purpose of this review is to examine the theory and assumptions that may limit the use of bioelectrical impedance analysis in such individuals. RECENT FINDINGS: There is currently insufficient validation of bioelectrical impedance analysis equations in obese individuals with body mass indices greater than 34 kg/m. Several factors limit the application of bioelectrical impedance analysis in morbidly obese individuals. Obese individuals have a relatively high amount of extracellular water and total body water, which may overestimate fat-free mass and underestimate fat mass. Central body fat will generally overestimate the percentage of fat-free mass and underestimate the percentage of fat mass in overweight and obese adults with the use of prediction formulas developed in normal weight individuals. SUMMARY: A relatively increased amount of total body water and a relative increase in extracellular water will result in an underestimation of the percentage of body fat and an overestimation of fat-free mass in the morbid obesity state. A different body build disposition (mainly in those with severe abdominal obesity) will result in an overestimation of the percentage of body fat. New equations are needed to validate bioelectrical impedance analysis in morbidly obese patients.     

Resting energy expenditure is not increased in mildly hyperglycaemic obese diabetic patients

Resting energy expenditure (REE) is believed to be increased in type 2 diabetes, an increase that is associated with deteriorating glucose tolerance during its development. Meanwhile, insulin resistance, a state linked to obesity and observed in all type 2 diabetic patients, is associated with reduced REE. Our aim was to compare REE in obese patients with and without diabetes. REE, body composition (total body water, density, percentage fat and fat-free mass: 3-compartment model) and metabolic control were assessed in fifty obese Caucasian patients with diabetes (glycated haemoglobin level 7.6 (SD 1.5) %) and fifty obese patients who were non-diabetic. Despite being more overweight and younger, obese non-diabetic patients had an absolute REE (7.73 (SD 1.44) v. 8.12 (SD 1.37) MJ; P=0.17) and percentage fat-free mass similar to those of obese diabetic patients. Even when adjusted for differences in body composition, REE remained similar in both groups. Furthermore, REE (absolute and adjusted) was unaffected by both glucose level and control (glycated haemoglobin), with fat-free mass being the only determinant of REE. We conclude that REE is not necessarily increased by the presence of diabetes in obese people.     

The relationship between body fat mass and fat-free mass

It has been suggested that there is a curvilinear relationship between lean body or fat-free mass and body fat mass. In order to confirm this relationship, body composition was measured by determining body density and total body water using deuterium-labeled water in subjects varying widely in body fat mass. There were 29 males and 75 females with body mass index ranging from 20 to 66 kg/m2. The relationship between fat-free mass and fat mass appeared to be linear over the range of body fat from 10 to 90 kg: males R2 = 0.67 (p less than 0.0001) and females, R2 = 0.47 (p less than 0.0001). The amount of variance explained was not greater when the log of fat mass was used in place of fat mass alone. Multiple regression analysis demonstrated that the relationship between fat-free mass and fat mass remained significant (p less than 0.001) after adjusting for body height, age, and fat distribution. It is concluded that over the range of body fat extending from 10 to 90 kg there is a positive and linear relationship between fat-free body mass and fat mass.