“Isotonic" means having the same fluid pressure as your other bodily fluids like blood and tears. When you eat food, drink a beverage, or take a pill or capsule, your stomach must first secrete diluting juices, enzymes, hydrochloric acid, and at least one vitamin-binding protein to continue the process of digestion. Everything you eat and drink, including nutritional supplements, must be made isotonic before passing into your small intestine where it can be absorbed. Once becoming isotonic, muscular contractions of your stomach mix the contents until a reasonably uniform solution is achieved. This process can take anywhere from 40 minutes to four hours.