The three most important elements after RNY gastric bypass surgery are to meet your daily protein, fluid and vitamin requirements. Food is secondary because your body is converting your stored fat into the energy that drives your body. Thus you lose weight.
Weight loss is achieved after surgery through meal volume control. You begin at 2 ounces (1/4 cup) per meal and gradually over the next year and a half increase the volume to 1 cup per meal. With this minuscule amount of food, it is next to impossible to meet your daily protein requirements by food alone, so therefore you need to rely on supplements such as protein shakes.
Many people experience problems eating and drinking after surgery. Two of the medical conditions that can contribute to this problem is the development of strictures and ulcers. So if you find that your problem is extreme (such as constant vomiting) then I would recommend working this problem out with your surgery team. That is why they are there.
The transition to hard foods (such as chicken and steak) can be rather rough. As a result I have relied on softer foods (such as high protein chili and soups). I have included a few recipes at the end of the following article. http://www.breadandbutterscience.com/Surgery.pdf