Yes, soft drink can make you fat if you drink it too much. Why? Because soft drink is rich in sugar. Usually drinks always use aspartame for sweetener and sucrose for the sugar. In soft drinks, they usually use high-fructose corn syrup, sucrose, and sugar substitute (only for diet). Soft drinks are called "soft" in contrast to "hard drinks". There are still some alcohol left in soft drink for only 0.5%. Soft drink is rich in sugar so, it makes people feel better because in instance soft drink gives energy and make your body release serotonin. Serotonin is a neurotransmitter that makes people happy). University of Texas found that soft drinks are increasing the risk of obesity in average of 32.8%, but in diet coke (Free sugar soft drink) also increase the risk of obesity in higher average, 54.5%. So we can conclude that soft drinks are a bit better than diet coke. Most of the soft drink have 250 calories/ 600 ml and they don't have any nutrition or minerals but it contains sugar and caffeine. So we can conclude that soft drink makes you fat. You can still drink it but not too much.
Not only fat, you can be diseased. Even a permanent diseased.