"... obesity is like global warming. In both cases, advocates of 'doing something' oversimplify complex science, and advocates of doing nothing use compexity to obfuscate the existence of real problems."
I liked this phrase, even if I think it does oversimplify things.
As part of my job I have to make decisions about product architecture. A lot of the time the need for decisions is preceeded by the "must do something about XYZ" coming from the Sales and Marketing group. Nevertheless, decisions need to be made, and it is not the specific allocation of resources to pursue multiple goals that is difficult. The most difficult decisions are the ones that commit the architecture to a direction with high switching-cost. In the absence of complete information about future requirements, two approaches may be equivalent in satisfying the currently known requirements. Each may offer benefits that the other one does not. The drawbacks of the approaches may be known upfront, but the likelihood of these theoretical drawbacks becoming issues is unknown. Thus, coming the team to a course of action is to take a chance on the likelihood of one set of drawbacks becoming actual issues vs. another set of drawbacks. That is only one dimension; however. We also need to take into account the cost of fixing the issues, if it becomes necessary, and of the relative resource consumption and ROI of one approach vs. another in general.
Same issues apply to policy formulation. Dieting is more popular than exercise because it offers many of the same benefits - as stressed by the key word "overweight" -- with low switching costs and possibility of achieving results without altering one's lifestyle. Exercise may offer more benefits, but clearly demands more resources and their longer application than dieting, at least in its current formulation and execution form. Perhaps if everyone biked to work and ran to lunch exercise would have a relatively low cost, but going to the gym, for months and years, is a pretty expensive proposition in terms of time and opportunity cost.
What people tend to do in the private sector is to run progressively bigger PoC (proof of concept) projects. This is comparable to doing immersive studies, but with a clearly formulated requirements and result acceptability. Perhaps what is needed is a coordinating authority to lay out a plan to determine not whether obesity is bad for you, or how bad it is [says this grossly overweight person], that would develop a set of PoCs by multiple vendors (diet, exercise, public policy gurus) to show what the costs and benefits of their approaches are when applied to this particular organization (town, state, country). Many of the vendors do PoC for free. I think it would not be unreasonable to have McDonalds, Bally's, and Education department pitch in to pay for these projects. After all, McDonalds does not really sell hamburgers, they sell "value meals" and "56 second average serving time" [from my local McD.]