If everyone gained 200-220 lbs overnight, I would expect worldwide economic collapse. While Toby_Aus brings up some good points, there's other points too.
In most cases I'd expect folks to still be able to fit into cars, though buses and public transit capacity might be a problem in areas that regularly see over 50% capacity, since I'd assume everyone would, on average take up twice the space.
However, he overlooked the most major problem. Most folks will NOT have clothes that fit, if everyone gained 200 lbs overnight. It would mean that even regardless of one's job, you will be unable to even go into public to get to the job or run errands in the first place. Even if you can telecommute, you still need to be presentable on video.
If the delivery drivers no longer have clothes that fit, not to mention the e-commerce retail workers, it won't be possible to order larger clothes online so you could venture forth into public again. Since no one could even go and operate the infrastructure, it won't even be possible to just put all the garment factories into overdrive. Even if that were possible, it'd likely take years to get clothes out to everyone.
But, if it was somehow possible to get past this very serious problem, I'd expect a few major changes to occur over the next decade or so.
I'd expect most gyms to eventually fail as many members may simply give it up, though some will probably remain. Most fitness instructors will probably have to give up that job.
Restaurants will likely start serving much larger portion sizes, and buffets may become more common. Packaged food manufacturers would likely discontinue their smallest packaging sizes and introduce larger package sizes. Perhaps vending machines will only offer 1L bottles and no longer sell 20 fl. oz. bottles or 12 fl. oz. cans.
Many motor vehicles may be redesigned to have larger, wider seats. Seatbelts for the center of a bench seat will likely disappear. A typical sedan may thus only seat up to possibly 4 individuals.
Refurbishing and expanding public transit in some areas will be extremely expensive. It will be a very unpleasant experience in places like Chicago or New York City until this public works project is completed.
Furniture manufacturers will have a field day, because of unprecedented demand they can't fill fast enough.
High fashion designers in New York City, Paris, and Milan may have to spend a lot of time coming up with new designs, if some designs can't be accommodated to fit 400 lb bodies.
Schools and universities may have to offer more courses online, since desks will have to be larger and the rooms may no longer be large enough to hold the same number of desks as before. They will have to spend millions of dollars to build larger facilities.
Retailers may have to spend time, effort, and money to rearrange store shelves for wider aisles.
Skyscrapers may need to be redesigned to accommodate elevators with twice as many square feet inside.
I would also expect very heavy investment in superior food distribution infrastructure, since currently, spoilage in transit is still a severe problem.
I would expect some commerce and industries to either fail completely or become far less common, but a lot of other industries would have to work overtime. Not just furniture and clothing manufacturers, but construction as well.
Of course, this would never happen.
However, if everyone was to consistently gain 20 lbs a year, there wouldn't be this major shock, but I would expect the other changes to take place. In fact, some of these changes are taking place already, just at a much slower rate because the annual average weight gain is much lower than 20 lbs/yr.
3 years
