The human metabolic response to chronic ketosis without caloric restriction: Preservation of submaximal exercise capability with reduced carbohydrate oxidation

New strategies in sport nutrition to increase exercise performance

“…Original interest in LCHF for sports performance stemmed from an 1983 study which measured exercise capacity in 5 well-trained cyclists before and after 4 weeks of a ketogenic LCHF diet [75]. Despite conditions that should have favoured a benefit to endurance (additional 4 weeks of training, overnight fasting and water only during cycling, very moderate intensity ~60% VO2max workloads), there was no mean improvement in time to exhaustion over the baseline values completed with a high carbohydrate diet.…”

“…Despite conditions that should have favoured a benefit to endurance (additional 4 weeks of training, overnight fasting and water only during cycling, very moderate intensity ~60% VO2max workloads), there was no mean improvement in time to exhaustion over the baseline values completed with a high carbohydrate diet. Moreover, the results were skewed by a large increase in endurance in one subject, and the authors also noted that the enhanced utilisation of fat and sparing of carbohydrate at moderate intensity was "a limitation of the intensity of exercise that can be performed" and a "throttling of function near VO2max" [75].…”

Physical exercise as a modulator of adaptation to low and high carbohydrate and low and high fat intakes

“…Adjustment of macronutrient intakes can elicit shifts in plasma and muscle substrates in as few as 12 h. Starling et al (1997) observed signi®cantly increased concentrations of muscle glycogen and lower concentrations of muscle triglycerides within one day after athletes followed a 120 min cycling bout with a high carbohydrate diet (83% carbohydrate, 5% fat) consumed over 12 h. Conversely, muscle glycogen decreased and intramuscular triglycerides increased in a separate trial when a high fat diet (16% carbohydrate, 68% fat) was consumed following exercise. Interventions in which fat intake comprised between 50 ± 85% of caloric intake for durations of 5 d ± 7 w also showed decreased muscle glycogen and increased muscle triglycerides as well as increased plasma FFA's, increased beta-hydroxy butyrate, and lower plasma lactate levels (Helge et al, 1996;Muoio et al, 1994;Phinney et al, 1983;Starling et al, 1997). Resting blood glucose levels typically did not differ due to diet (Helge et al, 1996;Phinney et al, 1983;Starling et al, 1997).…”

“…Interventions in which fat intake comprised between 50 ± 85% of caloric intake for durations of 5 d ± 7 w also showed decreased muscle glycogen and increased muscle triglycerides as well as increased plasma FFA's, increased beta-hydroxy butyrate, and lower plasma lactate levels (Helge et al, 1996;Muoio et al, 1994;Phinney et al, 1983;Starling et al, 1997). Resting blood glucose levels typically did not differ due to diet (Helge et al, 1996;Phinney et al, 1983;Starling et al, 1997). Correspondingly, resting insulin values were not signi®-cantly altered by dietary intervention although insulin action could be expected to vary between individuals consuming a high fat diet vs a high carbohydrate diet (Cutler et al, 1995;Rosholt et al, 1994).…”

“…However, no additive effect on enzyme activity was seen with inclusion of endurance training in the intervention (Helge & Kiens, 1997). One of the more extreme and frequently cited high fat trials was conducted by Phinney et al (1983). Phinney contends that the reported inability to maintain or enhance endurance performance on a high fatalow carbohydrate intake is attributable to failure to allow adequate time on a high fat diet for physiological adaptations to evolve.…”