As carbohydrate availability and muscle glycogen content are primarycomponents of metabolism andexercise performance, restriction ofendogenous carbohydrate availabilitywould seem to adversely affectstrenuous exercise performance. Thisstudy examined the effects of a verylow carbohydrate high fat (VLCHF)diet on cardiorespiratory andmetabolic responses during highintensity interval training (HIIT)．

Eighteen, moderately trainedmales were recruited. The subjectswere randomized to either remain on a western based mixed diet or to begin a VLCHF diet (eight percent carbohydrates, 29% protein and 63% fat) for four weeks. HIIT sessions occurred three times per week for four weeks and involved a 10-minute warm-up at 60% VO2max, followed by five, high-intensity repetitions, consisting of three minutes at 100% VO2max, separated by 1.5 minutes of passive recovery (work to rest ratio, 2∶1), for a total of 34 min. A maximal incremental treadmill test was performed at baseline and after two and four weeks of training. Heart rate, oxygen uptake, respiratory exchange ratio, total time to exhaustion and maximal VO2max were measured.

Changes in body mass averaged 4.7 kg in the VLCHF group and 0.8 in the control group, while body fat percentages were reduced by 3.2% and 1.1%, respectively. The VO2max increases were 3.1 ml/kg/min in the VLCHF group and 1.5 ml/kg/min in the control group.

This study found no adverse effects on any aspect of performance in subjects consuming a high-fat diet for four weeks.