The 7 glass beakers represent what the stomach looks like when it's filled with 500 calories. The beakers contain butter or oil, meat, cheese, rice, corn, potatoes and candy. One way in which we satisfy the hunger drive is to fill the stomach completely. This triggers the stretch receptors in the stomach. As the stomach becomes full, these receptors send a signal to the brain communicating to the brain that the bulk (volume) of the food that we ate is sufficient. When we consume a diet that restricts calories or portion size, 500 calories of oil or meat/processed foods barely fills the stomach and does not trigger or send any signals to the brain. Thus, we are forced to overeat an enormous amount of calories in order to trigger these receptors.
In contrast, 500 calories of whole plant foods fills the stomach completely, making it very difficult to overeat. The desire to overeat isn't related to our lack of willpower, but to our body giving us the wrong signals. These signals are constantly telling us to over-eat, because we haven't triggered our stretch receptors. Cutting back on portion size, counting calories, and using will power can only last so long before we're back to our old eating habits. My blog, How Stomach Receptors Help us Lose Weight, explains this concept in greater detail and provides many helpful videos and resources.