The human stomach can hold about 33 ounces of food and liquid, according to The Washington Post. At rest, it is about the size of a closed human fist, but can expand to the size of a full water balloon.
Restricting food portions over time can reduce the stomach's capacity by about 30 percent, according to Allan Geliebter, senior research scientist at the New York Obesity Research Center at St. Luke's Hospital, Columbia University. On the other hand, chronic overeating can cause the stomach to stretch over time, allowing room for more food and making dieting more difficult. Chow.com states that when a stomach is pushed to its limit, it can hold up to a gallon or 4 liters of food.