Polysiloxane: potential noncaloric fat substitute; effects on body composition of obese Zucker rats.

Phenylmethylpolysiloxane (PS), a noncaloric, nonabsorbable liquid oil, was studied for effects on body comparison as fat substitute in the diet. Two groups of female obese Zucker rats were fed either a control low-fat (LF) or an experimental diet containing PS (22% wt/wt) incorporated into LF. Two additional groups were fed either PS or cellulose (CE) in diet providing equivalent caloric dilution. Rats on PS lost weight whereas LF control rats gained. Dissectible fat and adipocyte size of PS were smaller than those of LF. Food intake, body water, and adipocyte number did not differ between PS and LF. Body protein on PS increased only in proportion to weight. When both diets were diluted, PS animals lost more weight than CE controls despite similar food intakes, suggesting absorption of calorigenic substances derived from partial digestion of CE but not PS by intestinal microflora. Obese rats did not compensate for caloric dilution with PS.

TOBEC methodology for body composition assessment: a cross-validation study.

The accuracy of prediction equations for estimating lean body mass (LBM) from total-body electrical conductivity (TOBEC) was examined by cross-validation. Two samples of adults, aged 18-35 yr, were drawn from separate geographic locations. LBM was determined by densitometry and TOBEC was measured with TOBEC II instrument. LBM and TOBEC were highly correlated in both samples (r = 0.96 and 0.97). Cross-validation of LBM prediction equations was accomplished by exchanging equations and comparing predicted LBM values. There was a mean difference of 0.974 kg LBM between the two equations (p less than 0.0001). Thus, data from 157 subjects were pooled and one equation was developed that incorporated height (cm), sex (males = 0, females = 1), and the zero-, first-, and second-order Fourier coefficients (FC0, FC1, and FC2) of the TOBEC phase value: LBM, kg = -36.410 + (-1.324 X sex) + (0.01185 X (FC1(0.5)xht)) + (12.347 X FC2(0.5)) + (0.0627 X FC0)-(0.9232 X FC2) This equation, developed from 157 subjects, accounted for 96% of the variability in LBM and had a standard error of estimate of 2.17 kg LBM.

Role of brown adipose tissue in thermogenesis induced by overfeeding a diet containing medium chain triglyceride.

The role of brown adipose tissue in the mechanism of medium chain triglyceride (MCT)-induced thermogenesis was investigated. Under anesthesia, the interscapular brown adipose tissue (IBAT) was excised in male Sprague-Dawley rats, and the animals were fitted with gastrostomy tubes. After a 10-day recovery period, the animals were divided into two groups: one group received a diet containing MCT as 50% of calories, and the other group received an isocaloric diet containing long chain triglyceride (LCT). The diets were fed for 6 wk at a level of calorie intake that was 150% of the ad libitum intake of a parallel control group. During the last week of the study, resting and norepinephrine (NE)-stimulated O2 consumption and CO2 production were measured in a Noyons diaferometer. At the end of 6 wk, the animals were weighed and killed. The individual fat pads were dissected and weighed, and an aliquot of the right retroperitoneal fat pad was used to measure adipocyte size and number. The results showed that body weight and adipocyte size (but not adipocyte number) were significantly smaller in the MCT-fed compared to the LCT-fed animals. Resting as well as maximal NE-stimulated oxygen consumption values were significantly higher in the MCT-fed than the LCT-fed rats. It is concluded that the enhanced thermogenesis induced by MCT persists despite the absence of IBAT and that the phenomenon is likely related to more extensive oxidation of MCT- in contrast to LCT-derived fatty acids, thus leading to increased oxygen consumption, enhanced dissipation of energy as heat and diminished efficiency of weight gain and deposition of body fat.

Naltrexone and human eating behavior: a dose-ranging inpatient trial in moderately obese men.

To investigate the effects of the long-acting opiate antagonist naltrexone on spontaneous human eating behavior, eight moderately obese male paid volunteers were housed in a hospital metabolic unit for 28 days and offered palatable foods ad lib by a platter service method. Under double-blind conditions, equally divided doses of 100, 200 and 300 mg naltrexone, or an acetaminophen placebo, were administered twice daily in tablet form for 3-day periods each, according to a Latin Square design. The doses of naltrexone resulted in decreases of daily caloric intake from placebo level, but these reductions were neither statistically significant nor dose-related. When the averaged effects of the doses were compared to placebo, five subjects showed intake reductions but the overall intake reduction of 301.5 +/- 198.1 kcal/day (mean +/- SEM) was not statistically significant. Naltrexone administration failed to selectively alter intakes of individual meals and snacks or macronutrient consumption patterns. During active drug periods, subjects lost 0.62 +/- 0.22 lb over 3 days, while during the placebo period, subjects gained 0.46 +/- 0.68 lb. However, there was no reliable change of basal metabolic rate as a function of naltrexone administration. The present results, which indicate that naltrexone administration is relatively ineffective in reducing food intake and inducing body weight loss in obese humans, are thus in contrast with reports that administration of opiate antagonist agents promote significant reductions of food intake and attenuations of body weight gain in experimental animals.

Insulin increases body fat despite control of food intake and physical activity.

The effect of experimentally induced hyperinsulinemia on body composition was studied in rats with food intakes precisely controlled by intragastric feeding and physical activity manipulated by sedation with chlordiazepoxide (CDP). Male Sprague-Dawley rats (n = 38) were fitted surgically with gastrostomy tubes. After 8 days the animals were divided into four groups. Group 1 received daily injections of protamine-zinc insulin; group 2 received daily injections of saline; group 3 received the same insulin doses as group 1 plus daily administration of CDP mixed with the diet; group 4 received daily injections of saline plus CDP in the diet. All groups were tubefed identical amounts of semiliquid diet via gastrostomy. Physical activity was measured by electronic monitor. After 4 wk the rats were killed. The insulin-treated groups (1 and 3) had significantly larger fat depots and larger mean fat cell size than the noninsulin-treated groups (2 and 4). This increase in fat occurred concurrently with a decrease in carcass protein and water. Physical activity, as measured, was unaltered by insulin but was significantly reduced by CDP. Treatment with CDP only increased the dorsal fat depot and liver weight but had no significant effect on total dissected fat depots and had a reductive effect on carcass protein. In conclusion insulin treatment enhanced the efficiency of conversion of energy intake into fat energy stores.

A new method for estimation of body composition in the live rat.

Measurement of total body electrical conductivity (TOBEC) has been used to estimate lean and fat content of meat based on the principle that electrical conductivity of lean tissue is far greater than that of fat. This approach was used to estimate body composition of live rats. An instrument designed for commercial analysis of ground meat (DjMe 100) was used to measure TOBEC in 30 male Sprague-Dawley rats (197-433 g). Individual TOBEC values were obtained in 20 seconds and repeated twice for each rat. The animals were then killed with ether, hair was shaved, lungs collapsed and body density measured hydrostatically. Carcasses were homogenized and analyzed for fat, nitrogen, and water. A high correlation was found between TOBEC and lean body mass by densitometry (r = .97) and between TOBEC and fat-free mass derived from direct carcass analysis (r = .97). Rats weighing up to 450 g could be accommodated in this particular instrument. Measurement of TOBEC should prove useful in estimating body composition and monitoring its changes in live rats and other small laboratory animals.

Overfeeding with medium-chain triglyceride diet results in diminished deposition of fat.

The study was designed to determine whether overfeeding rats with a diet containing medium-chain triglyceride (MCT) as the major fat source (45% of calories) would impede the expected gain in weight and body fat as compared to rats overfed with isocaloric amounts of diet containing long-chain triglyceride (LCT). For 6 wk rats were fed either MCT diet or LCT diet twice daily via a gastrostomy tube. MCT-fed rats gained 20% less weight (P less than 0.001) and possessed fat depots weighing 23% less (p less than 0.001) than LCT)-fed rats. Mean adipocyte size was smaller (p less than 0.005) in MCT- than in LCT-fed rats. Weights of carcass protein and water were similar for both groups as were concentrations of serum insulin and levels of physical activity. The decreased deposition of fat in the MCT-fed rats may have resulted from obligatory oxidation of MCT-derived fatty acids in the liver after being transported there via the portal vein, leaving almost no MCT derivatives for incorporation into body fat. MCT may have potential for dietary prevention of human obesity.

Enhanced thermogenesis and diminished deposition of fat in response to overfeeding with diet containing medium chain triglyceride.

The mechanism whereby overfeeding with diet containing medium chain triglyceride (MCT) results in diminished body weight and fat was studied. Fifteen male Sprague-Dawley rats were fitted under anesthesia with gastrostomy tubes and divided into two groups. One group was fed MCT diet, the other an isocaloric diet containing long chain triglyceride (LCT) in excess (150%) of spontaneous calorie intake. Both diets, fed for 6 wk, derived 50% of calories from fat. Basal and norepinephrine (25 micrograms/100 g) stimulated 02 consumption and CO2 production, as well as metabolic rate were measured. After the rats were killed, total dissectible fat and fat cell size and number were determined. MCT rats gained 15% less weight than LCT controls (p less than 0.001). Total dissectible fat was significantly lower (p less than 0.001) in MCT group, as was mean adipocyte size (p less than 0.001). Resting and maximal norepinephrine-stimulated 02 consumptions were 39.7 and 22.1% higher in MCT than in LCT group, respectively. Resting and norepinephrine-stimulated metabolic rates were 38.8 and 22.2% higher in MCT than LCT fed rats, respectively. Overfeeding MCT diet results in decreased body fat related to increased metabolic rate and thermogenesis.