Short-term dietary energy restriction reduces lean body mass but not performance in physically active men and women.

We studied the effect of moderate, short-term energy restriction on physical performance in physically fit men (n = 13) and women (n = 11) in a controlled clinical research setting with a metabolic kitchen, exercise testing laboratory and training facility. The experiment consisted of a 10 d baseline period followed by either 2 wk of dietary energy restriction (750 kcal/d; n = 16) or energy balance (control; n = 8). During this 24 day study, exercise energy expenditure averaged 465 +/- 5.7 kcal/d in all subjects and was accomplished through treadmill running at a self-selected pace. Body weight was maintained in the control group (-0.36 +/- 0.24kg), but energy restriction resulted in weight loss of -1.29 +/- 0.16 kg (p < 0.001). There was a trend for lean body mass to decline more in the energy restriction group (p = 0.093), accounting for 61% of the weight loss, and urinary nitrogen excretion also tended to be higher in the energy restriction vs. control group (i.e., 13.2 +/- 1.1 vs. 11.2 +/- 1.0g/d; p = 0.089). Muscle strength (leg & shoulder press; 1 repetition maximum) was maintained or increased during the energy restriction period. Muscle endurance, assessed by leg squats to fatigue, and 5 mile run time improved following two weeks of energy restriction or balance. Anaerobic capacity (Wingate Test) increased slightly in the restriction (+ 368 +/- 219 joules) but declined in the control group 649 +/- 288 joules; p<0.05). We conclude that short-term (2 weeks) moderate energy restriction (approximately 750 kcal/d) results in weight loss but does not impair performance in physically fit young men and women.

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

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+/-3 (s.e.)y, mean body fat=25.0+/-2.8 (s.e.)%), five obese (O) (26+/-3 y, 44. 4+/-1.7%), and five post-obese (PO) (22+/-1 y, 32.2+/-3.0%) women cycled for 60 min at 60-65% peak VO2. To identify the specific 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 VO2 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.