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Effects of Ad libitum Low-Carbohydrate High-Fat Dieting in Middle-Age Male Runners
Heatherly, Alexander J.; Killen, Lauren G.; Smith, Ashton F.; Waldman, Hunter S.; Seltmann, Christie L.; Hollingsworth, Angela; O'Neal, Eric K.
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2018
10.1249/MSS.0000000000001477
ISBN: 0000000000 PMID: 29112626
Abstract:
PURPOSE This study examined the effects of a 3-week ad libitum high fat (∼70% of calories), low carbohydrate (\textless50 g/day) diet (LCHF) on markers of endurance performance in middle-aged, recreationally competitive male runners. METHODS All subjects (n = 8) following their normal HC diet had anthropometric measures assessed and completed 5, 10-min running bouts at multiple individual race paces in the heat while physiological, metabolic variables and perceptual responses were recorded. After 20-min of rest, participants completed a 5-km time trial (5TT) on a road course. Subjects then consumed a LCHF diet for 3 weeks and returned for repeat testing. RESULTS Body mass and 7-site skinfold thickness sum decreased by approximately 2.5 kg (p \textless 0.01) and 13 mm (p \textless 0.05) after LCHF. Rectal temperature was higher after the first 10-min of exercise (37.7 ± 0.3 °C vs. 37.3 ± 0.2 °C) in the HC diet but did not differ at any other time with LCHF. Heart rate and perceptual measures did not display any consistent differences between treatments excluding thirst sensation for LCHF. Respiratory exchange ratio and carbohydrate oxidation declined significantly while fat oxidation increased after LCHF for every pace (p \textless 0.01). There was no significant difference (p = 0.25) in 5TT performance, but LCHF (23.45 ± 2.25 min) displayed a trend of improved performance versus HC (23.92 ± 2.57 min). CONCLUSION Improved body composition and fat oxidation from LCHF potentially negate expected performance decrement from reduced carbohydrate utilization late in exercise for non-elite runners. An acute decrease in training capacity is expected; however, if performance improvement is not exhibited after 3 weeks, diet cessation is suggested for negative responders.
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