A high carbohydrate diet negates the metabolic effects of caffeine during exercise.

We tested the hypothesis that unrecognized nutritional factors might influence the serum free fatty acid response to caffeine. The time course and extent of the serum free fatty acid response to a fatty meal alone, to caffeine ingestion after a high carbohydrate meal, or to caffeine in combination with either a fatty meal or a high carbohydrate meal (the latter following 3 d of a high carbohydrate diet) were studied in six trained runners. The metabolic response to 120 min of exercise at 75% of maximum oxygen consumption after caffeine ingestion was also studied in runners after a high carbohydrate diet and ingestion of a high carbohydrate meal. Serum free fatty acid levels were highest 3 h after caffeine ingestion alone and were lower following a fatty meal with or without caffeine ingestion (P less than 0.05). The high carbohydrate diet combined with the ingestion of a high carbohydrate meal prevented the expected rise in serum free fatty acid levels following caffeine ingestion. The metabolic response to prolonged submaximal exercise was also not influenced by the ingestion of caffeine by subjects who had eaten a high carbohydrate diet. Nutritional factors, in particular the state of the body carbohydrate stores and the simultaneous ingestion of carbohydrate, influence the response of serum free fatty acid levels to caffeine ingestion.