On one of the Yahoo! Groups someone asked about pelleted diets. They were concerned that liver damage might occur over time. They can't feed their bird fresh foods because it won't eat them. With a little coaxing they can get their bird to eat a smoothie. Here is our response:
Honestly, no one knows the answer to that question. Most of the nutritional formulation of pellets is derived from what we know of poultry husbandry. Harrison's pellets were formulated by the same vet who commissioned the text clinical avian medicine. That's the pellet we supply our birds.
I've changed the diet of many birds here at the sanctuary. When they come to us they are often used eating terrible things. One relinquisher told me "She will be easy to feed. She eats anything." I am not a junk food junkie and don't have things like frosted flakes, cookies, and Cheetos around the sanctuary. That was the cockatoo's choice in food. I've had this bird with me now for about three months and she is eating the mash that I make of organic vegetables, grains, and beans. The process of changing a bird's diet can take a long time. The above mentioned bird gets health-food varieties that are the equivalent of the junk food items that she is used to along with the mash. Finding low sugar and salt replacements nearly drove me nuts but I had no choice: this wonderful bird destroys her feathers and without comfort food she mutilates.
The key to changing a bird's diet is to be aware of what they like and find ways to make small changes. With Sugar, the Moluccan aptly named for her diet, I presented many different kinds of cooked food. She readily ate cooked yams. From there I began slowly adding other items to the yams until she was eating almost the same mash as the others. By the way, I do vary items in the mash and the flavors because birds seem to tire of the same food every day.
As with any training the changes are made in baby steps, small approximations. You begin with things they already eat and make slight changes observing the results. This process can go on for a long time.
One umbrella cockatoo with us, Coco, would only eat bananas, oats, and peanut butter from a spoon held for her when she came here. Now she holds her own spoon and eats the mash on her own. She wouldn't eat peanut butter, bananas and oatmeal today; her taste in food is completely different now.
You can change your bird's diet. You can. If you have ever seen a trained killer whale this should make you realize that there is science behind shaping behavior. The trainer had no special gift from a higher power: the trainer used proven scientific methods. Behavior training works! Doing what I do I would be up the creek without a paddle if I had not learned to use it.
Since your bird is already eating a smoothie. That's where you should start.