I make smoothies all the time and I have never had a problem with them. I have never had any weight fluctuations with them either and I have been doing the Paleo/Primal thing for over 4 years now. I agree with Owly in that a banana and some berries shouldn't be too bad for you. Just as long as you are using whole foods and no added sugar I would think its okay from time to time. Here are my two go-to recipes.
Recipe #1
1/2 cup of blueberries
1 small banana
1/2 cup of coconut milk
2 handfuls of kale
1/4 cup of ice
Recipe #2
1/2 cup of coffee
1/2 cup of coconut milk
1 small banana
1 tablespoon almond butter
2 Tbs. raw cacao
1 scoop unsweetened whey
1/4 cup of ice
"If man made it, don't eat it" - Jack Lallane
People say I am on a "crazy" diet. What is so crazy about eating veggies, fruits, seafood and organ meats? Just because I don't eat whole wheat and processed food doesn't make my diet "crazy". Maybe everyone else with a SAD are the "crazy" ones for putting that junk in their system.