Gastric by-pass diet following surgery, weeks four and beyond?

Talk to you surgeon. After gastric bypass every surgeon has their own protocol for advancing your diet. At 1 month postop i start to add meats like chicken and fish. But talk to your doctor about what you should eating.
Vitamins&small meals. By this point, you should be beyond the sips-of-liquids stage, and should be tolerating some small foods. However, your intestines will not absorb a fair amount of what you eat, and the parts that absorb iron, vitamin A,D,E, and K are most likely bypassed. So continue on the vitamin and mineral supplements. Eat small meals so as not to "stretchout" your stomach and undo the weight you have lost.