Food in the stomach is first pushed slowly past the stomach lining into the small bowel. There the food is mixed, like soap, with bile. "It washes the fat," Dr. Oz explains. "It makes it so you can absorb it. As that bile mixes with the food that you've taken in, it begins to get absorbed across the wall. As it gets absorbed, if it's healthy oils, for example, it makes your liver very happy. But if this is full of trans fats and hydrogenated fats and foods that aren't good for you, it's very toxic to the liver."
In the picture above you can see the liver has turned from rich red to white, signaling an unhealthy, fatty liver. You can also see an expanding omentum, leaving a big belly.
Next food moves through the small intestine and into the large bowel. A valve between the two can slow this movement. "That [valve] is stimulated by fiber," Dr. Oz says. "The reason people who have breakfast lose weight is because they have fiber in their diet. Food doesn't come through quite as quickly so you don't feel hungry as quickly."
Fiber—from foods like whole grains and fruit—makes you need fewer calories in your meal while still making you feel full.