Supplemental creatine is a popular ergogenic aid, but its benefits are limited. Research has shown creatine to be effective in increasing muscle strength and power during brief, high intensity exercise lasting about one minute or less (such as sprinting and weight lifting). It is believed to work by improving ATP metabolism. Creatine will not benefit endurance athletes. A common side effect is weight gain, which can make athletes feel sluggish. Other reported side effects include diarrhea, muscle cramps, and dehydration. For the most part, however, creatine is considered safe when taken in recommended dosages. Athletes often take creatine in phases. During the loading phase, athletes consume 20-25 grams (in 5 gram increments) per day for 4-7 days. During the maintenance phase, 2-5 grams per day are consumed. Creatine can be obtained through animal foods, such as meat and fish, but in amounts less than 2 grams. Creatine may be slightly more effective when combined with glucose; thus it is frequently sold in combination with carbohydrate. Individual responsiveness to creatine may vary. Vegetarians, who may consume little creatine in the diet, may experience a more pronounced response to creatine supplementation than non-vegetarians.