Look it is a lot more complex then just serving size. There are multiple parts to the obesity problem. Everything from serving size, what we actually eat and drink, amount of daily exercise, and even a strong possibility that antibiotic content in food we eat is a contributing factor. Simply banning or regulating serving sizes is still a drop in the bucket.
I would be impressed if Bloomberg had an actual publicized plan of action that was more involved. Banning sugary drinks over 16 oz is going to do diddly squat. People are still going to over indulge in sodas. Crowing it is fighting obesity is disengenious to the issue at large. This looks and sounds like a typical move to look like he is doing something useful about the issue.
You want to fight obesity. Get people healthier food in general. Healthy food is on average more expensive then most of the stuff that is bad for you. I am not talking just fast food I am talking about what you can buy at a grocery in general.
Next get people up and off their asses and moving around and exercising at least 30 minutes a day. Even modest amounts of exercise does wonders for weight control and general health.
Look into various food additives like excessive amounts of high fructose corn syrup for example and other high sugar content foods. Hell if you start examining food labels even meat for HFCS content you would be shocked how much of our food contains the crap.
There are some studies that suggest HFCS is another contributing factor to the obesity epidemic for how regular consumption affects peoples diets. Kinda hard to eat it in moderation when damn near everything can have it in it.
Even the U.S. military has some concerns about the obesity epidemic for a good reason.
Something in general needs to be done but the soda ban in NYC is just political showmanship nothing more. It's usefulness is severly limited.