Meal usually means that some food was/will be eaten at some point in time. Example: 'I'm really hungry. It's 9 in the evening and I only head one meal today, at 10 in the morning'. In other words I ate food only once. Food has a much more general meaning. Example: 'People need air, food and water to survive'

well, cheese, meat, rice, and etc are foods, but breakfast, dinner, and lunch are meals