Energy metabolism, testosterone and corticosterone in white-crowned sparrows | SpringerLink
The mechanisms by which sex hormones cause changes in body composition are unclear. Alternatively, sex steroid deficiency could result in lean tissue loss and thus reduced energy expenditure. Our objective was to examine the independent and combined effects of acute testosterone and estrogen withdrawal on respiratory exchange ratio RER and resting energy expenditure REE in men The objective of the study was to examine the independent and combined effects of acute estrogen and testosterone withdrawal on respiratory exchange ratio RER and resting energy expenditure REE in men.
We conclude that abrupt changes in sex steroids does not change resting substrate oxidation, indicating that changes that can be observed after more prolonged periods of deficiency are most likely due to direct effects of sex steroids on body composition. Decreases in sex steroid production that accompany aging may contribute to decreases in lean body mass and increases in fat mass 1 — 3.
With aging, resting energy expenditure REE , which makes up a significant amount of total daily energy expenditure, also decreases. Although changes in body composition contribute to changes in REE and substrate oxidation, changes in REE and substrate oxidation can occur prior to changes in body composition, such as seen in response to growth hormone replacement 4.
To test this hypothesis it is necessary to measure these parameters prior to body composition changes, which is difficult in the setting of gradual declines in sex steroids that occur naturally. To overcome this problem we chose a model of acute sex steroid withdrawal and timed the indirect calorimetry measurement to occur before significant changes in body composition could take place.
If no changes in RER or REE could be detected after 3 weeks of abrupt decreases in sex steroids this would strongly suggest that sex steroids affect body composition, which in turn affect REE rather than the other way around.
Written informed consent was obtained from 60 individuals with 54 participants completing the study. On entry into the study, participants were given an intramuscular injection of 7. The participants simultaneously received 2. After this three week run-in period, participants received a 2 nd dose of leuprolide acetate and were randomized to four groups: Reliable determination of REE was conducted as previously described 6.
Briefly, indirect calorimetry DeltraTrac Metabolic Cart, Yorba Linda, CA measurements were conducted over a 30 minute period after a 12 h fast and after a 30 minute period of bedrest 6. They reported an average decrease in fat free mass of 2. The differences in energy expenditure that would cause this change in body composition were estimated as follows: An average gain of 1. Comparisons of baseline characteristics were performed using a one-way analysis of variance ANOVA with post hoc Tukey test.
SPSS for Windows version Participants who completed the study were well matched for age, weight and BMI Table 1. Participants did not report any changes in activity or dietary patterns throughout the intervention. Sex steroid concentrations, respiratory exchange ratio and resting energy expenditure before and after 3 weeks of hormone treatment.
Estrogen and testosterone concentrations were not tested for statistical significance because they are not random variables. These findings lead us to conclude that sex steroids are most likely to alter body composition directly rather than indirectly via changes in postabsorptive substrate oxidation. Others who have examined the effects of testosterone alone on energy and substrate metabolism over shorter periods of time also found no effect 9 , 10 , whereas over longer periods of time increases in REE have been seen with testosterone replacement We believe the present study is unique in that it examines the isolated and combined effects of physiological concentrations of testosterone and estrogen on REE and RER in a time frame short enough to avoid changes in body composition but long enough to be confident that detectable effects were not missed.
Body composition was not measured in this study because the three week period of sex hormone suppression is unlikely to produce detectable changes. Thus, while growth hormone replacement can increase REE before changes in body composition 4 , it appears sex steroids have effects on REE primarily by changing body composition 7.
The lack of effect of estrogen and testosterone on substrate oxidation indicate that changes in body composition that occur with falling sex steroid concentrations likely result from other sex hormone-associated perturbations in fat and muscle metabolism Longer term supplementation studies have consistently shown the influence of estrogen and testosterone supplementation on body composition.
Testosterone or estrogen therapy increases or maintains lean body mass and reduces the accumulation of subcutaneous and abdominal fat 2 , 3 , 13 — A limitation of this study is that we measured resting but not total daily energy expenditure. It is possible that sex steroids exert unique and specific metabolic effects on the other components of energy expenditure - thermic effect of food TEF or activity energy expenditure AEE.
The later could occur through changes in the efficiency of physical activity, which appears not to have been studied, or changes in the amount of physical activity. If reductions in physical activity occur they would more likely reflect effects of sex steroids on CNS regulation of this aspect of daily energy expenditure rather than a direct metabolic effect. In summary, our findings indicate that estrogen, testosterone or estrogen plus testosterone do not independently change REE or overnight postabsorptive substrate oxidation.
The effects of sex steroids on REE are most likely mediated by direct effects on body composition, either via direct effects on protein synthesis or via indirect effects on physical activity. Likewise, changes in metabolic rate with aging likely are not the direct result of changes in sex steroid concentration but rather due to body composition and perhaps other hormonal alterations.
How the milieu of changing levels of sex steroids with aging perturbs fat or muscle metabolism, independent of energy metabolism, remains an important area of investigation. The authors report no conflict of interest with regards to these studies. National Center for Biotechnology Information , U. Author manuscript; available in PMC Jun 1. Khosla , Louise K. McCready , and M D.
The publisher's final edited version of this article is available free at Obesity Silver Spring. See other articles in PMC that cite the published article. Abstract The mechanisms by which sex hormones cause changes in body composition are unclear. Introduction Decreases in sex steroid production that accompany aging may contribute to decreases in lean body mass and increases in fat mass 1 — 3. Materials and Methods Protocol Written informed consent was obtained from 60 individuals with 54 participants completing the study.
Table 1 Sex steroid concentrations, respiratory exchange ratio and resting energy expenditure before and after 3 weeks of hormone treatment. Open in a separate window. Lifestyle factors associated with age-related differences in body composition: Am J Clin Nutr.
Effects of androgen therapy on adipose tissue and metabolism in older men. J Clin Endocrinol Metab. Testosterone therapy prevents gain in visceral adipose tissue and loss of skeletal muscle in nonobese aging men. Relationship between GH-induced metabolic changes and changes in body composition: Regulation of bone turnover by sex steroids in men. J Bone Miner Res. Measurement reliability and reactivity using repeated measurements of resting energy expenditure with a face mask, mouthpiece, and ventilated canopy.
Testosterone deficiency in young men: Energy expenditure, sex, and endogenous fuel availability in humans. No effect of short-term testosterone manipulation on exercise substrate metabolism in men. Estrogen supplementation reduces whole body leucine and carbohydrate oxidation and increases lipid oxidation in men during endurance exercise. Growth hormone and testosterone interact positively to enhance protein and energy metabolism in hypopitutary men. Santosa S, Jensen MD. Why are we shaped differently and why does it matter?
Am J Physiol Endocrinol Metab. Exogenous androgens influence body composition and regional body fat distribution in obese postmenopausal women--a clinical research center study. Dose-dependent effects of testosterone on regional adipose tissue distribution in healthy young men. Body composition, visceral fat distribution and fat oxidation in postmenopausal women using oral or transdermal oestrogen. Support Center Support Center.