How and why people choose to eat particular foods

People choose the food they eat simply because they may have certain ingredients that they can't have. Some people may be allergic to different types of food. Some people just decide that they rather not eat things such as meat and others. How do they do this? I assume they check the calories and many more just to make sure they don't gain weight. They try to make sure they can keep a figure and that no food they eat will interfere with that. Also some people choose to not eat particular food because maybe they don't like it and think it's nasty. Maybe they choose to eat different food because a friend or family member may have tried it and suggested to others not to eat it.