There seems to be a lot of discussion and concern about how to know when babies are ready for solids, or if they are receiving enough milk from mom.
Here is some info which might be helpful:
Here is a wonderful book on babies/children's eating habits. Don't let the title fool you. This is a great read no matter what age you baby is and what your situation is:
Finally, here is a link on the caloric and fat values of milk, formula and other common baby foods. Keep in mind this list is ounce-per-ounce. So, even though avacado has more calories and fat per ounce that BM, it is not likely a baby will sit and eat 3, 4 or 5 ounces of avacado the way he would BM.
(This is not an LLL source)