The issue here is again assuming that studies and expert knowledge is required to determine whether drinking too much soft drinks and/or having a bad diet is bad for health and causes obesity.

Even if that was not obvious, which it is, it becomes so very quickly as you start putting on weight. Similarly, it is obvious and well-known that burning more calories means being able to eat more calories.

People know all that.

Those studies and the attempts at influencing results are mostly political. These studies are tools to influence policy. That's why you have plenty of studies paid for by plenty of pressure groups and which results magically serve the interests of these pressure groups (whatever the side of the argument, or the topic). If you want to have a law passed you need tools to help you. If you want to prevent that you also need tools.

Of course on scientific studies can be very important on many issues, but on this one really they are not to uncover anything Earth-shattering.