You don't have much control over your appetite, Dr. Grunvald says, since it's a physiological process. It's kind of like breathing -- sure, you can take long breaths, short breaths, deep breaths, and on, but you still have to breathe.
Same thing goes for eating. Some people naturally crave fruits and vegetables, while others have strong hankerings for the sugar- and fat-laden processed foods that are terrible for you. Some people rarely feel hungry, while others are ravenous multiple times a day; thanks to your genetics, there's no way to turn off these feelings.
Of course, people can control how they respond to their appetite, but when life gets in the way -- stress, hunger pangs, snacks in the break room -- it makes it that much harder to go against biology.