Is "stomach" used as a verb in general?
Yes, "stomach" is also frequently used as a verb. It means to consume something edible (like food) without feeling sick. In this video, the speaker has used "go ahead and eat as much as you can stomach" to mean that the contestants can eat as much food as they can without getting sick (throwing up). Ex: I have a weak body, so I can't stomach heavy or greasy food. Ex: I can't stomach smelly food.