1955 might be too late of a POD to make American food less centered on high-fat dishes. It might be in time to stop the spread of fast food, but people would still love fried chicken, barbecue, cheesy casseroles and meatloaves. They'd also continue to love hot dogs and hamburgers.
The latest POD I can see working is WW2. Rationing plus altering food sent to the troops could change the basic pattern of American eating to something a little healthier but equally acceptable. A Mediterranean diet like that of Italy could work; if it has to be within American cuisine, then I'd say a seafood-based cuisine might work (although that poses problems for inland states, where pork/beef would have to remain king), or perhaps a Mexican-inspired cuisine.
If 1955 is set in stone then a post-war diversification of tastes needs to happen faster than OTL. In a lot of cities "What do you want tonight?" is answered today with a country rather than a dish. If that view could be popularized fast and nationwide, including rural areas, then Americans might become accustomed to choosing between healthier cuisines than the old native foods. It'd be Thai one night, Chinese another, Italian, Japanese, and so on. There'd still be a place for regional cuisine -- Southern, Southwest, American Jewish, etc. There would actually be more emphasis on regional American cooking rather than a homogenized menu of burgers and double burgers.
Not that there's anything wrong with burgers.