Summer squash is 95 percent water, making it naturally low in calories and a good choice if you are trying to lose weight. A medium zucchini, for example, contains just 33 calories. It supplies a gram of protein and less than a gram of fat. The same size zucchini contains 6 grams of carbohydrates, 2 grams of which are dietary fiber. That makes zucchini a low glycemic food that will not spike your blood sugar, but will instead provide a steady source of glucose to your system.