It's important to include a variety of healthy foods in your blended diet. There are, however, some foods that just don't blend well.
There's nothing worse than realizing that you've added an ingredient into your blender that isn't breaking down as it should. Depending on the strength and effectiveness of your blender, there may be some foods to avoid or at least modify in order to achieve a smooth homogeneous blend.
1- Nuts. Use soft nuts like pecans or walnuts instead of harder nuts like almonds or hazelnuts. Better yet, use a smooth nut butter instead of whole nuts.
2- Dried fruit. Soak in water until soft (refrigerate as this may take several hours).
3- Stringy vegetables. Finely chop or remove fibrous strings.
4- Tough meats. Use soft protein sources like eggs, ground meats, cooked beans/lentils, or tofu.
5- Tough fruit and vegetable skins. Examples include squash skin, apple skin, thick potato skins. It's best to limit these. Not only are they hard to blend, they are also hard to digest.
Luckily, this list is quite short. The sky is the limit when it comes to making your blended meals. Remember that if you are having difficulty achieving a smooth blend, try running your blender longer (up to several minutes) to make sure all foods are properly pureed. To get started and to ensure nutritional adequacy, consider purchasing one of Natural Tube Feeding recipe books and get inspired to create your own blends for you or your tube fed loved-one.