The free market can only work if everybody had perfect information and no secrets. Otherwise whoever has more information can manipulate reality.
In particular, relevant to this thread, if you have a magical CSV file created by an Oracle associating every food available in US with how "healthy" they are and how much calory they provide, in order to build a 2500 calory diet that maximizes health and minimizes cost, you need to solve a knapsack-like problem. In this environment market will necessarily be a little random not because we don't have enough information but because we don't have enough computational power.
EDIT: I must also admit that I know absolutely nothing about economics. I'm a regular software engineer.
This is false; the typical free market advocate understands there is a limited role for government intervention. Basic examples: Police, fire services, military, currency, lighthouses.
In contrast, socialism can only work if the central planners have perfect information and no secrets. That's why it hasn't ever worked - information can't be centralized like that; the economy is too complex. So it ends up depending on a central actor to manipulate reality (see China today or any other socialist economy ever and the blatant lies in their economic statistics).
The issue with sugary drinks isn't that people lack information. The information is written on the side of every soda can; it is nearly a perfect-information situation. The issue is that people are irrational in other ways (related to time preference and inability to moderate impulses or re-evaluate habits).
People drink soda unhealthily not because they've been tricked by Coca Cola misinformation campaigns into thinking that soda is healthy.
Your view is that people think soda is healthy.
To describe the idea is to refute it. Ask a few soda drinkers if they think soda is healthy.
cough