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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.; Hollingsworth, Angela; Seltmann, Christie L.; O’Neal, Eric K.
Medicine & Science in Sports & Exercise: Post Acceptance: November 06, 2017
doi: 10.1249/MSS.0000000000001477
Original Investigation: PDF Only

AbstractPURPOSEThis study examined the effects of a 3-week ad libitum high fat (~70% of calories), low carbohydrate (<50 g/day) diet (LCHF) on markers of endurance performance in middle-aged, recreationally competitive male runners.METHODSAll 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.RESULTSBody mass and 7-site skinfold thickness sum decreased by approximately 2.5 kg (p < 0.01) and 13 mm (p < 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 < 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).CONCLUSIONImproved 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.

PURPOSE

This study examined the effects of a 3-week ad libitum high fat (~70% of calories), low carbohydrate (<50 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 < 0.01) and 13 mm (p < 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 < 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.

Corresponding Author: Eric O’Neal, Mailing Address: 1 Harrison Plaza, Florence, AL 35632, Phone: 256-765-4555. Email: eoneal1@una.edu

Funding for the current study was not aided by any grants, awards, or incentives by any outside organizations. The views and data presented in this manuscript are not necessarily that of the American College of Sports Medicine and are in no way under endorsement. All information that is presented in this manuscript are without falsification, manipulation, or fabrication. All data is reported accurately and honestly to the best of the authors’ knowledge.

Accepted for Publication: 4 October 2017

© 2017 American College of Sports Medicine