Substrate oxidation and availability during acute exercise in non‐obese, obese, and post‐obese sedentary females

Abstract

OBJECTIVE: This study compared fat oxidation rates during an acute bout of cycle ergometry exercise (E) typical of progressive fat oxidation in healthy, but sedentary, women of different obesity histories. DESIGN: Five never-obese (NO) (mean age 25 AE 3 (s.e.)y, mean body fat 25.0 AE 2.8 (s.e.)%), ®ve obese (O) (26 AE 3 y, 44.4 AE 1.7%), and ®ve post-obese (PO) (22 AE 1 y, 32.2 AE 3.0%) women cycled for 60 min at 60 ± 65% peak VO 2 . To identify the speci®c effects of E, a control trial consisting of 60 min of seated rest (R) was also performed. E and R trials were counterbalanced one month apart in the follicular phase and conducted following a 3 d normalized, eucaloric diet. MEASUREMENTS: Dual energy X-ray absorptiometry (DEXA) was used to determine body composition, and all were weight stable for at least eight weeks prior to experimentation. During both trials breath by breath measurements of VO 2 and RER were used to determine substrate oxidation and energy expenditure. Blood samples were collected for hormone and metabolite analysis before, and every 15 min during exercise or rest. RESULTS: All three groups showed a similar and progressive shift toward fat oxidation as exercise progressed. No group differences were observed for E energy expenditure or fat oxidation. Glycerol (P`0.0001) and free fatty acids (P`0.0001) increased similarly in all three groups, but PO maintained the highest free fatty acid level during exercise (group effect; P`0.01). E and R decreased (P`0.001 for both) insulin levels across groups, with lowest levels noted in PO and highest in O. Plasma epinephrine (P`0.0001) and norepinephrine (P`0.001) increased similarly during E in all three groups. Plasma growth hormone (GH) levels rose (P`0.05) during E, with a pronounced increase observed in PO. CONCLUSION: We conclude that exercise of equal relative intensity elicited similar fat oxidation rates among NO, O, and PO women, despite group differences in free fatty acid availability. The PO women's persistently lower insulin and higher plasma GH levels may have enhanced free fatty acid availability.

Substrate utilization during exercise in postmenopausal women on hormone replacement therapy

“…Froberg and Pederson (1984) found lower R values in women compared to men during continuous cycle ergometry at 80% of _ V V O 2max , an exercise intensity similar to that used in the present study. In addition, there was a substrate shift with exercise duration reported in this study that has been described in other studies of men and younger women (Ball-Burnett et al 1991;Coggan et al 2000;Ezell et al 1999;Powers et al 1980;Swan and Howley 1994). The shift has been attributed to an increased lipolysis with increased exercise duration due to alterations in hormone concentrations of catecholamines and insulin (Horton et al 1998;Tate and Holtz 1998).…”

“…When comparing results on equivalent fat energy expended for 30 min exercise bout (Fig. 5) they are consistent with the duration-dependent increased reliance on fat during steady-state activity of a moderate to vigorous intensity demonstrated in younger populations (Ball-Burnett et al 1991;Coggan et al 2000;Ezell et al 1999;Powers et al 1980;Swan and Howley 1994). Future studies should examine the effects of HRT in postmenopausal women on substrate utilization during and following exercise of different intensities and durations.…”

Aerobic training improves exercise-induced lipolysis in SCAT and lipid utilization in overweight men

“…This partly induces high plasma NEFA concentrations. Despite better lipid availability in this population, Ezell et al (10) did not find differences in lipid oxidation during exercise between obese and nonobese subjects. Few studies have assessed physical exercise effects on lipid oxidation in this population; most experiments associate hypocaloric diet (with great weight loss) with exercise training.…”

Sexual Dimorphism in Human Lipid Metabolism

“…However, the mechanism responsible for the blunted lipolytic response to exercise associated with obesity may differ in men and women. First, we (30) and others (32,33) found that exercise causes a smaller increase in plasma epinephrine concentration in obese than in lean men, whereas the catecholamine response during exercise does not differ in lean and obese women (29,31,34). Furthermore, unlike obese men (35)(36)(37), adipose tissue ␤-adrenergic receptor sensitivity is decreased in obese women (30), whereas ␣-adrenergic receptor stimulation during exercise is greater in both obese men and women compared with lean subjects (38).…”