Diffusion and Osmosis Kit

The membranes that surround all cells only allow certain substances to go in or out. Small molecules, like iodine, pass readily through cell membranes while large, bulky molecules, such as starch, do not. However, we don’t “eat” huge quantities of iodine but we do eat starch. If we eat starch but it cannot pass through cell membranes, what good is it as a food? If starch is not really used by the human body, because it can’t get inside our cells, then why do many athletes participate in “starch/carbohydrate loading” prior to a competition? Why do people become obese if they eat a lot of starchy food? Experiments will be conducted to discover the answers to such questions.