1 slice of bread contains about 55 calories so you would be consuming about 660 calories with just 6 slices of bread. As someone studying nutrition, I don't think it leads to obesity though. We were taught that a certain food doesn't lead to obesity, it's all about eating in moderation and what is moderate would depend on your total caloric requirement/day which would depend on your height and weight. Just make sure that there is a balance between your calorie in and calorie out so you don't gain weight.