Effects of Ad libitum Low-Carbohydrate High-Fat Dieting in Middle-Age Male Runners

Nov 8, 2017Medicine and science in sports and exercise

Effects of Eating a Low-Carb, High-Fat Diet as Desired in Middle-Aged Male Runners

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Abstract

Body mass decreased by approximately 2.5 kg after a 3-week low-carbohydrate, high-fat diet.

Skinfold thickness sum decreased by 13 mm after the low-carbohydrate, high-fat diet.
Rectal temperature was higher during the first 10 minutes of exercise on a high-carbohydrate diet but not at other times with the low-carbohydrate, high-fat diet.
Carbohydrate oxidation declined significantly, while fat oxidation increased for all paces after the low-carbohydrate, high-fat diet.
There was no significant difference in 5-km time trial performance between the two diets, though a trend toward improved performance was observed after the low-carbohydrate, high-fat diet.

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PURPOSE: This study examined the effects of a 3-wk ad libitum, low-carbohydrate (<50 g·d) high-fat (~70% of calories) (LCHF) diet on markers of endurance performance in middle-age, recreationally competitive male runners.

METHODS: All subjects (n = 8) after their normal high-carbohydrate (HC) diet had anthropometric measures assessed and completed five 10-min running bouts at multiple individual race paces in the heat while physiological variables, metabolic variables, and perceptual responses were recorded. After 20 min of rest, participants completed a 5-km time trial on a road course. Subjects then consumed an LCHF diet for 3 wk and returned for repeat testing.

RESULTS: Body mass and seven-site skinfold thickness sum decreased by approximately 2.5 kg (P < 0.01) and 13 mm (P < 0.05) after LCHF diet. Rectal temperature was higher after the first 10 min of exercise (37.7°C ± 0.3°C vs 37.3°C ± 0.2°C) in the HC diet but did not differ at any other time with LCHF diet. Heart rate and perceptual measures did not display any consistent differences between treatments excluding thirst sensation for LCHF diet. RER and carbohydrate oxidation declined significantly, whereas fat oxidation increased after LCHF diet for every pace (P < 0.01). There was no significant difference (P = 0.25) in a 5-km time trial performance, but LCHF diet (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 diet potentially negate expected performance decrement from reduced carbohydrate use late in exercise for nonelite runners. An acute decrease in training capacity is expected; however, if performance improvement is not exhibited after 3 wk, diet cessation is suggested for negative responders.

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