Protein From Supplements

I'm 3 months post-op and am finding that many of my meals contain very little protein. Fruits and veggies are so much easier for me to eat, and dense, protein-packed foods make me feel nauseated. I'm getting my protein by shakes and shots instead of foods. I know that my dr wants me to be cutting back on the shakes, but why does it matter? If I'm staying within my calorie range and eating healthy foods, does it matter how I get the protein?