1.
Differences in the metabolic status of healthy adults with and without active brown adipose tissue.
Zhang, Q, Ye, H, Miao, Q, Zhang, Z, Wang, Y, Zhu, X, Zhang, S, Zuo, C, Zhang, Z, Huang, Z, et al
Wiener klinische Wochenschrift. 2013;(21-22):687-95
Abstract
BACKGROUND Previous studies have proven the existence of active brown adipose tissue (BAT) in adults; however, its effect on systematic metabolism remains unclear. AIM: The current study was designed to investigate the differences in the metabolic profiles of healthy adults with and without active BAT using positron emission tomography-computed tomography (PET-CT) scans in the un-stimulated state. METHODS A cross-sectional analysis was performed to assess the health of adults using PET-CT whole-body scans at Huashan Hospital Medical Centre between November 2009 and May 2010. A total of 62 healthy adults with active BAT were enrolled in the BAT-positive group. For each positive subject, a same-gender individual who underwent PET-CT the same day and who had no detectable BAT was chosen as the negative control. Body composition was measured, and blood samples were collected for assays of metabolic profiles and other biomarkers. RESULTS In both the male and female groups, BAT-positive individuals were younger and had lower body mass indexes, fasting insulin, insulin resistance, and leptin, but a greater level of high-density lipoprotein cholesterol compared with the negative controls. In the male group, body fat content and levels of tumor necrosis factor-α were significantly lower in the BAT-positive than in the negative control group. CONCLUSIONS The healthy adults with active BAT in an un-stimulated state had favorable metabolic profiles suggesting that active BAT may be a potential target for preventing and treating obesity and other metabolic disorders.
2.
Exercise increases the proportion of fat utilization during short-term consumption of a high-fat diet.
Hansen, KC, Zhang, Z, Gomez, T, Adams, AK, Schoeller, DA
The American journal of clinical nutrition. 2007;(1):109-16
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Abstract
BACKGROUND Increases in energy substrate oxidation occur at different rates after an increase in either fat or carbohydrate intake. Adaptations to increased fat intake are relatively slow and are influenced by activity level. OBJECTIVE We tested the hypothesis that increased levels of daily activity, as influenced by added exercise, would have a graded effect on the rate of compensatory adjustment to a short-term high-fat diet. DESIGN Daily total energy expenditure and macronutrient oxidation were measured at 3 physical activity levels (PALs) by using a whole-room indirect calorimeter in 10 adult women as they transitioned from a 1-d low-fat (30% of energy) control diet to a 4-d high-fat (50% of energy) diet. The 3 PALs (1.4, 1.6, and 1.8) were provided daily by increases in bicycle ergometer exercise time. RESULTS An increase in physical activity led to a greater increase in the nonprotein respiratory exchange ratio (-0.047 +/- 0.02, -0.064 +/- 0.02, and -0.071 +/- 0.02; P < 0.0001) and 24-h fat oxidation (113 +/- 24, 125 +/- 19, and 147 +/- 20 g/d; P < 0.0001) for PALs of 1.4, 1.6, and 1.8, respectively, after the transition from the low-fat control diet to the high-fat diet. Random-effects analysis found a significant (P = 0.003) relation between PAL and the compensatory fat oxidation response to a high-fat diet. CONCLUSIONS Amounts of exercise consistent with the Institute of Medicine's recommendations reduce the time required to match fat oxidation to a change in the percentage of fat in the diet. Because short-term consumption of high-fat diets is thought to contribute to excess fat accumulation, regular exercise should be protective and should help maintain a healthy body composition.