The difference is portion sizes for example aam 100g cottage cheese(reduced fat) on the 790 325g reduced fat cottage cheese. Also on 790 plan you get 1/2 pint of skimmed milk daily on aam you dont.
AAm is used on 5th week of doing ss and 790 is the next plan up from this.
Ruthlet explained all info (good girl for listening lol) but i would suggest looking at your yellow cambridge book and having chat with your cdc
julesrush