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Biomedical subjects

E Ravussin

Publications and source records attributed to E Ravussin.

At least 163 records · Page 9Linked to original sources
PubMed1992

Food intake measured by an automated food-selection system: relationship to energy expenditure.

Measuring food intake in a laboratory usually involves limited food choices. An automated food-selection system with two vending machines containing a large variety of foods was used to measure food intake in 10 male volunteers (31 +/- 6 y, 69.2 +/- 7.1 kg, 18 +/- 7% fat, mean +/- SD) on a metabolic ward. The effect of carbohydrate, fat, and protein intakes on 24-h energy expenditure (24EE) and substrate oxidations was measured in a respiratory chamber during day 4 of weight maintenance and day 7 of ad libitum intake. Ad libitum intake resulted in a 7-d overfeeding of 6468 +/- 3824 kJ/d above weight-maintenance requirements, leading to a 2.3 +/- 1.2-kg gain. The 10,975 +/- 3774 kJ excess energy intake on day 7 of ad libitum intake caused a 1205 +/- 920 kJ/d increase in 24EE (delta 24EE = 0.17 x delta intake - 695; r = 0.71, P less than 0.02). Of the excess carbohydrate intake, 74% was oxidized (r = 0.86, P less than 0.001), whereas excess fat intake was not. Carbohydrate and protein stores are regulated whereas excess fat intake is channeled to fat stores.

Adult↗
PubMed1992

Spontaneous physical activity and obesity: cross-sectional and longitudinal studies in Pima Indians.

Healthy, nondiabetic Pima Indians [103 males, 77 females; 27 +/- 6 (SD) yr, 97 +/- 25 kg, 33 +/- 9% body fat] were studied in a respiratory chamber in which spontaneous physical activity (SPA) was measured by two microwave sensors. SPA, defined as the percentage of time the subjects were active, varied widely from 4.4 to 17.5%. It was higher in males (9.3 +/- 2.0%) than in females (8.6 +/- 2.3%; P less than 0.05) and was not related to body fatness in either sex. However, SPA accounted for a significant portion of the daily energy expenditure (24-h EE) in males (1,389 +/- 423 kJ/day) and females (1,163 +/- 351 kJ/day) and correlated positively with 24-h EE adjusted for differences in fat-free mass, fat mass, age, and sex (r = 0.42, P less than 0.0001). In 88 siblings, family membership accounted for 57% of the variance in SPA (r(i) = 0.57, P less than 0.02). Body composition was reassessed in a subgroup of 123 subjects (65 males, 58 females) 33 +/- 14 mo later. In males only, SPA correlated inversely to the rate of subsequent body weight change (r = -0.25, P less than 0.05) and the rate of fat-mass change (r = -0.35, P less than 0.005). We conclude that spontaneous physical activity is a familial trait that may play a role in the pathogenesis of obesity.

Adult↗
PubMed1992

Concomitant interindividual variation in body temperature and metabolic rate.

There is significant variation in metabolic rate in humans, independent of differences in body size, body composition, age, and gender. Although it has been generally held that the normal human "set-point" body temperature is 37 degrees C, these interindividual variations in metabolic rate also suggest possible variations in body temperature. To examine the possibility of correlations between metabolic rate and body temperature, triplicate measurements of oral temperatures were made before and after measurement of 24-h energy expenditure in a respiratory chamber in 23 Pima Indian men. Fasting oral temperatures varied more between individuals than can be attributed to methodological errors or intraindividual variation. Oral temperatures correlated with sleeping (r = 0.80, P < 0.0001), and 24-h (r = 0.48, P < 0.02) metabolic rates adjusted for differences in body size, body composition, and age. Similarly, in the 32 Caucasian men of the Minnesota Semi-Starvation Study, oral temperature correlated with adjusted metabolic rate, and the interindividual differences in body temperature were maintained throughout semistarvation and refeeding. These results suggest that a low body temperature and a low metabolic rate might be two signs of an obesity-prone syndrome in humans.

Adult↗
PubMed1992

Energy expenditure of elite female runners measured by respiratory chamber and doubly labeled water.

To determine whether female athletes have unusually low energy requirements as suggested by many food intake studies, energy expenditure (EE) and intake were assessed in nine elite distance runners [26 +/- 3 (SD) yr, 53 +/- 4 kg, 12 +/- 3% body fat, and 66 +/- 4 ml.kg-1.min-1 maximal O2 uptake]. Subjects were admitted to a metabolic ward for 40 h during which 24-h sedentary EE was measured in a respiratory chamber. Free-living EE was then assessed by the doubly labeled water method for the next 6 days while the women recorded all food intake, daily body weight, and training mileage (10 +/- 3 miles/day). Energy intakes estimated from free-living EE (2,826 +/- 312 kcal/day) and body weight changes (-84 +/- 71 g/day) averaged 221 +/- 550 kcal/day in excess of those calculated from food records (2,193 +/- 466 kcal/day). The energy cost of training (1,087 +/- 244 kcal/day) was calculated as the difference between free-living EE and 24-h EE in the respiratory chamber (1,681 +/- 84 kcal/day) corrected for the thermic effect of food of the extra energy intake. These data do not support the hypothesis that training as a distance runner results in metabolic adaptations that lower energy requirements in women.

Adaptation, Physiological↗
PubMed1992

Lower sedentary metabolic rate in women compared with men.

Since females have a greater prevalence of obesity compared with males, the question arises whether females have lower metabolic rate than males after adjusting for differences in body weight and composition. 24-h energy expenditure (24EE), basal metabolic rate (BMR), and sleeping metabolic rate (SMR) were measured in a respiratory chamber in 235 healthy, nondiabetic Caucasian subjects (114 males, 121 females). Body composition was determined by hydrodensitometry. 24EE was 124 +/- 38 kcal/d (P less than 0.002) higher in males than females after adjusting for differences in fat-free mass, fat mass, and age. Spontaneous physical activity was not significantly different between males and females. Since adjusted 24EE was 106 +/- 39 kcal/d (P less than 0.01) higher in females during the luteal phase of the menstrual cycle compared with females during the follicular phase, energy expenditure was analyzed in a subset (greater than 50 yr) to minimize the confounding effect of menstrual status. 24EE (160 +/- 66 kcal/d; P less than 0.03), BMR (116 +/- 45; P less than 0.02), and SMR (208 +/- 68 kcal/d; P less than 0.005) were higher in males compared with females of the older subset after adjusting for differences in body composition, age, and activity. In summary, sedentary 24EE is approximately 5-10% lower in females compared with males after adjusting for differences in body composition, age, and activity.

Adult↗
PubMed1992

Resting metabolic rate and body composition of Pima Indian and Caucasian children.

Since a low metabolic rate (for a given body size and body composition) is a risk factor for body weight gain and obesity is prevalent among Pima Indians, we have tested whether Pima Indian children have a low resting metabolic rate (RMR) as compared to Caucasian children. Body composition (bioelectrical resistance) and RMR were measured in 43 Pima Indian children (22 male/21 female, mean +/- s.d. 9.9 +/- 1.1 years) and 42 Caucasian children (21 male/21 female, 9.7 +/- 1.2 years). Pima children were taller (143 +/- 9 vs. 137 +/- 8 cm, P less than 0.001), heavier (48.6 +/- 15.8 vs. 32.9 +/- 7.8 kg, P less than 0.001) and fatter (39 +/- 10 vs. 24 +/- 7% fat, P less than 0.001) than Caucasians. Absolute values of RMR were higher in Pimas than in Caucasians (6234 +/- 1201 vs. 5171 +/- 715 kJ/day, P less than 0.001), but similar when adjusted for differences in body size, body composition and sex. Contrary to our hypothesis, we did not find a decreased RMR in Pima children when compared to Caucasian children. Therefore, the high prevalence of obesity in Pima children at age 10 suggests that excess energy intake and/or low levels of physical activity might be the major aetiological factor. However, this study does not exclude the possibility that a low metabolic rate might be a predisposing factor at an earlier age.

Basal Metabolism↗
PubMed1992

Obesity in Pima Indians. Distribution characteristics and possible thresholds for genetic studies.

We examined distribution characteristics of the body mass index (BMI; weight/height; kg/m2) in a sample of 1128 male and 1372 female Pima Indians aged 15-65 years. We found that women had a higher mean and variance of BMI than men. From commingling analyses, we determined that the distribution of BMI could be accounted for either by a single skewed distribution or by a mixture of multiple normal components. These component distributions may be used to define provisional thresholds in selecting families for genetic studies. To ensure genetic segregation of obesity predisposing genes in Pima families will require that some members have BMIs > or = 40 kg/m2.

Adolescent↗
PubMed1991

Racial differences in the relation between blood pressure and insulin resistance.

BACKGROUND: Insulin resistance and the concomitant compensatory hyperinsulinemia have been implicated in the pathogenesis of hypertension. However, reports on the relation between insulin and blood pressure are inconsistent. This study was designed to investigate the possibility of racial differences in this relation. METHODS: We studied 116 Pima Indians, 53 whites, and 42 blacks who were normotensive and did not have diabetes; the groups were comparable with respect to mean age (29, 30, and 31 years, respectively) and blood pressure (113/70, 111/68, and 113/68 mm Hg, respectively). Insulin resistance was determined by the euglycemic-hyperinsulinemic clamp technique during low-dose (40 mU per square meter of body-surface area per minute) and high-dose (400 mU per square meter per minute) insulin infusions. RESULTS: The Pima Indians had higher fasting plasma insulin concentrations than the whites or blacks (176, 138, and 122 pmol per liter, respectively; P = 0.002) and lower rates of whole-body glucose disposal during both the low-dose (12.7, 17.1, and 19.5 mmol per minute; P less than 0.001) and the high-dose (38.0, 43.1, and 45.7 mmol per minute; P less than 0.001) insulin infusions. After adjustment for age, sex, body weight, and percentage of body fat, mean blood pressure (calculated as 1/3 systolic pressure + 2/3 diastolic pressure) was significantly correlated with the fasting plasma insulin concentration (r = 0.42) and the rate of glucose disposal during the low-dose (r = -0.41) and high-dose (r = -0.49) insulin infusions (P less than 0.01 for each) in whites, but not in Pima Indians (r = -0.06, -0.02, and -0.04, respectively) or blacks (r = -0.10, -0.04, and 0.02, respectively). CONCLUSIONS: The relations between insulinemia, insulin resistance, and blood pressure differ among racial groups and may be mediated by mechanisms active in whites, but not in Pima Indians or blacks.

Adult↗
PubMed1991

Body composition in Pima Indians: validation of bioelectrical resistance.

To assess the validity of bioelectrical resistance (BR) in an obese population, body composition was determined by both hydrostatic weighing and by BR in 156 Pima Indian volunteers representing a wide range of body weight (46.1-202.6 kg) and body composition (11-52% fat). A predictive equation was derived by use of data on height, BR, weight, age, and sex from 130 randomly selected volunteers and was applied to the remaining 26 volunteers. When compared with the manufacturer's software, the new equation increased correlations with hydrostatic weighing for predicting percent body fat and fat-free mass (FFM) from 0.70 to 0.92 and 0.79 to 0.97, respectively. The manufacturer's software underestimated FFM by 5.3 +/- 8.6 kg (P less than 0.05) when compared with FFM derived from hydrostatic weighing whereas the new equation improved the accuracy to -0.1 +/- 3.3 kg (NS). There were no significant effects of fluid intake (700 mL) or breakfast consumption on body composition as determined by BR. BR represents a simple and accurate way to assess body composition in Pima Indians with our newly derived equation.

Adipose Tissue↗
PubMed1991

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.

Adipose Tissue↗
PubMed1991

Energy cost of physical activity on a metabolic ward in relationship to obesity.

The energy cost of physical activity on a metabolic ward was derived from the difference between the energy requirement to maintain body weight on a metabolic ward and sedentary 24-h energy expenditure measured in a respiratory chamber in 56 nondiabetic male subjects. The cost of physical activity was negatively correlated with body weight (r = -0.67, P less than 0.0001) and with percent body fat (r = -0.48, P less than 0.0005). In a subgroup of 15 subjects selected for strict weight stability (rate of daily weight change less than +/- 35 g/d), similar negative correlations were observed between energy cost of activity and body weight (r = -0.61, P less than 0.01) and percent body fat (r = -0.51, P = 0.05). The ratio of active to sedentary energy expenditure, an index of physical activity, was also negatively correlated with body weight and percent body fat (r = -0.74, P less than 0.002 and r = -0.61, P less than 0.02, respectively). These results suggest that heavier subjects on a metabolic ward are less active and expend less energy in physical activity than do lighter subjects.

Adipose Tissue↗
PubMed1991

Studies of the etiology of obesity in Pima Indians.

Studies have been conducted on various metabolic characteristics of lean and obese Pima Indians, including studies of fat-cell morphology, glucose transport, and lipolysis; lipoprotein lipase activities; sodium-potassium ATPase in red cells, adipocytes, and fibroblasts; lipids and lipoprotein metabolism; fatty acid metabolism; and sterol balance. Insulin concentrations, insulin binding, insulin action on glucose disposal, fatty acid metabolism, and islet function were compared in lean and obese individuals, and the relationship between insulin resistance and muscle morphology was explored. To explore potential abnormalities in energy balance, calorie intake and gastric emptying were compared in lean and obese Pimas and measurements of energy expenditure were performed. The data suggest that there are multiple metabolic differences that accompany obesity in Native Americans. A lower metabolic rate was a determinant of future weight gain, and abnormalities in use of free fatty acids and cell insulin action were suggested, which emphasize the need for further studies in these areas.

Adenosine Triphosphatases↗
PubMed1991

Muscle mitochondrial morphology, body composition, and energy expenditure in sedentary individuals.

To investigate whether differences in metabolic rate are related to differences in muscle mitochondrial morphology and/or to differences in in vitro muscle respiration, we studied 17 healthy Caucasians, covering a wide range of body weight and composition [9 males, 8 females; body wt 96 +/- 37 (SD) kg; body fat = 28 +/- 10%]. Central and peripheral mitochondrial volume density (Vmit c and Vmit p, respectively) and the ratio of mitochondrial outer surface to volume of mitochondria (SVmit c in center and SVmit p at periphery) were determined by stereological analyses of transmission electron micrographs from samples of the vastus lateralis. There was no relationship between mitochondrial morphology or muscle respiration and 24-h energy expenditure, basal metabolic rate, or sleeping energy expenditure adjusted for differences in fat-free mass, fat mass, age, and sex. Although total body fat was not associated with muscle cell morphology, central distribution of body fat [waist-to-thigh circumference ratio (W/T)] correlated negatively with Vmit c (r = -0.58, P = 0.01), SVmit c (r = -0.59, P = 0.01), and SVmit p (r = -0.48, P = 0.05). W/T was also negatively related to muscle respiration (r = -0.59, P = 0.01). Despite the lack of relationship between metabolic rate and muscle mitochondrial morphology, central distribution of body fat is associated with lower mitochondrial density and larger mitochondria in skeletal muscle and is associated with a decreased oxidative capacity of muscle.

Adult↗
PubMed1991

Effect of endurance training on sedentary energy expenditure measured in a respiratory chamber.

The effect of endurance training on 24-h energy expenditure (EE), basal metabolic rate (BMR), sleeping metabolic rate (SMR), and the thermic effect of food (TEF) was assessed in a respiratory chamber where only spontaneous physical activity (SPA) was allowed. Results from 20 highly trained male endurance athletes (25 +/- 5 yr, 178 +/- 7 cm, 70 +/- 8 kg body wt, 64 +/- 7 kg fat-free mass) were compared with those of 43 untrained males who were matched for age (28 +/- 6 yr), height (175 +/- 5 cm), weight (73 +/- 13 kg), and fat-free mass (62 +/- 8 kg). Subjects were admitted to a metabolic ward, fed a weight-maintenance diet, and refrained from physical activity for at least 2 days before measurements. No significant differences were found with respect to 24-h EE (2,126 +/- 186 vs. 2,154 +/- 245 kcal), BMR (1,808 +/- 342 vs. 1,709 +/- 329 kcal), SMR (1,523 +/- 120 vs. 1,555 +/- 188 kcal), or TEF (24.9 +/- 9.2 vs. 21.3 +/- 6.7% of ingested calories; these values included the energy cost of arousal) between trained and untrained subjects, respectively, before or after adjusting for differences in body composition. Neither the 24-h respiratory quotient nor the level of SPA differed between the two groups. No relationship was found between maximal aerobic capacity and metabolic rate adjusted for differences in fat-free mass and fat mass. These results do not support an effect of fitness level on EE measured under sedentary conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Energy expenditure by doubly labeled water: validation in lean and obese subjects.

The doubly labeled water (2H2(18)O) method to assess energy expenditure in free-living conditions has been successfully validated against gas exchange measurements in lean healthy volunteers in both sedentary conditions and during sustained heavy exercise. However, no data are available on obese subjects. We therefore compared the 2H2(18)O method with indirect calorimetry (respiratory chamber) in 12 male subjects covering a wide range of body weight and composition (61-190 kg, 7-41% fat). Isotope pool sizes and elimination rates were calculated from 18O and 2H enrichments in baseline urine samples and in 7-h, 11.5-h, and daily postdose urine samples using the multipoint slope/intercept method. Results were corrected for isotopic fractionation. Mean 7-day energy expenditure in the respiratory chamber varied from 1,851 to 4,105 kcal/day. The doubly labeled water method tended to underestimate energy expenditure (-2.5 +/- 5.8%, not equal to 0, range -14 to +4%), with the larger underestimate observed in heavier and fatter subjects (r = -0.82 and -0.68, P less than 0.02, respectively). The underestimation in heavier subjects might be related to larger sequestration of deuterium during fat synthesis. In conclusion, the doubly labeled water method is a suitable and accurate method to measure energy expenditure in free-living conditions but might provide a slightly underestimated figure in fatter subjects.

Adipose Tissue↗
PubMed1991

Ethnic differences in sympathetic nervous system-mediated energy expenditure.

The impact of sympathetic nervous system (SNS) activity on energy expenditure (EE) was evaluated in nondiabetic Caucasian and Pima Indian men while on a weight-maintenance diet using two approaches as follows. 1) The relationship between 24-h EE, measured in a respiratory chamber, and 24-h urinary norepinephrine was studied in 36 Caucasians [32 +/- 8 (SD) yr, 95 +/- 41 kg, 22 +/- 13% fat] and 33 Pimas (29 +/- 6 yr, 103 +/- 28 kg, 30 +/- 9% fat). There was no difference between the two groups in 24-h EE (2,422 vs. 2,523 kcal/24 h) and in urinary norepinephrine (28 vs. 31 micrograms/24 h), even after adjusting for body size and composition. Twenty-four-hour EE correlated significantly with 24-h urinary norepinephrine in Caucasians (r = 0.78, P less than 0.001) but not in Pimas (r = 0.03), independent of fat-free mass (FFM), fat mass, and age. 2) The effect of beta-adrenoceptor blockade with propranolol (120 micrograms/kg FFM bolus and 1.2 micrograms.kg FFM-1.min-1 for 45 min) on the resting metabolic rate (RMR) was evaluated in 36 Caucasians (30 +/- 6 yr, 103 +/- 36 kg, 25 +/- 11% fat) and 32 Pimas (28 +/- 6 yr, 100 +/- 34 kg, 27 +/- 10% fat). The RMR was similar in the two groups (2,052 vs. 1,973 kcal/24 h) even after adjustment for FFM, fat mass, and age and dropped significantly after propranolol infusion in Caucasians (-3.9%, P less than 0.001) but not in Pimas (-0.8%, P = 0.07).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1991

Insulin resistance associated with lower rates of weight gain in Pima Indians.

UNLABELLED: Insulin resistance is commonly associated with obesity and noninsulin-dependent diabetes. Whereas it predicts the development of diabetes, its effect on body weight change is unknown. We measured glucose disposal rates at submaximally- and maximally-stimulating insulin concentrations in 192 nondiabetic Pima Indians and followed their weight change over 3.5 +/- 1.8 y (mean +/- SD). RESULTS: (a) Insulin-resistant subjects gained less weight than insulin-sensitive subjects (3.1 vs. 7.6 kg, P less than 0.0001). (b) The percent weight change per year correlated with glucose disposal at submaximally-(r = 0.19, P less than 0.01) and maximally-stimulating (r = 0.34, P less than 0.0001) insulin concentrations independent of sex, age, initial weight, and 24-h energy expenditure; the correlations were stronger for glucose oxidation than for glucose storage. (c) Weight gain was associated with an increase in insulin resistance more than four times that predicted from the cross-sectional data. We conclude that insulin resistance is associated with a reduced risk of weight gain in nondiabetic Pima Indians.

Adolescent↗