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This study evaluated the effect a ketogenic diet had on the exercise capacity of eight healthy men. Subjects were placed in either a mixed diet group or a ketogenic group. The ketogenic diet consisted of 50% of calories derived from fat, 45% from protein and 5% from carbohydrate. After three days on the diet, subjects performed an exercise test in which they worked out at varying intensities. In comparison to subjects on the mixed diet, those on the ketogenic diet displayed increased maximal oxygen consumption (the amount of oxygen taken in by the lungs per minute, which is an excellent predictor of overall fitness). Moreover, the ketogenic subjects showed a decreased respiratory exchange ratio, meaning more fat was burned for energy. Finally, the ketogenic group showed a shift in the lactate threshold toward higher exercise loads. When the amount of lactate in the blood reaches a certain level at a certain intensity, performance is impaired; this point occurred after a longer duration of time at a higher intensity level of exercise. Blood lactic acid levels before and after exercise as well as blood pH were also lower. The ketogenic diet also lowered insulin concentration. The authors concluded that a short-term ketogenic diet does not impair, but in fact increases, aerobic exercise capacity, as indicated by an elevated maximal oxygen consumption and elevated lactate threshold.