I've been eating fastfood for 6 months,3 times a week and gained only stomach weight.i've fast metabolism,so i'm concernd,could it be medical problem?

Your plan is?: are you trying to gain weight? you are eating fast food to gain weight! what you mean by stomach weight? waist. eating fast food will not make you gain a healthy weight, it will only increase your cholesterol, and your lipids in your blood, and increase your chance of heart disease. if you are concern about your metabolism problems , you can check with a local physician to run some test.