Gastroparesis, a condition in which the stomach digests food too slowly or not at all, can develop as a side effect of diabetes, digestive surgery, cancer treatments, eating disorders, endocrine or neurological problems or certain medications. If you have gastroparesis, your doctor will place you on a diet that doesn't strain your digestive system.A smoothie appropriate for the full liquid phase of the gastroparesis diet is not the same as one you may get from a restaurant, juice bar or coffee shop. These smoothies should consist primarily of fluid and yogurt. The yogurt can be fruit-flavored, made from regular or plant milk, sugar-free, frozen or in the form of kefir, but it cannot contain chunks of fruit or ingredients like granola. Use milk, plant milk, water or juice as the fluid. For additional flavor, add extracts such as vanilla or almond extract, fruit syrup, flavored gelatin powder or pudding mix. To give the smoothie a thicker consistency, you can blend the mixture with ice or with frozen, very ripe bananas.