Side note #1: My son's nutritionist said that hemp protein is the best powdered protein available. That soy products should be used sparingly especially in boys (something to do with it raising their estrogen levels and possibly effecting their chances of cancer because of that) and I believe the whey protein is not preferred if you are trying to cut back on gluten and certain grains. We already had the whey type in the house and she did say to get Hemp instead. I am new to altering my son's diet, but I do know his nutritionist knows her stuff.

Side note #2: Nutritionist also recommended books to us, "eating for autism" and "food chaining"

Side note #3: If you do not use a blender/magic bullet and just shake this drink very well it will still have quite a few chunks of protein mixed in. My son doesn't care, but I would!

Side note #4: The nutritionist also had stated that frozen fruit is the best option because it is usually picked at the peak season so it has the best nutritional quality and is usually a better deal and better for smoothies since it is frozen. :)

My son sees a nutritionist at a local childrens hospital. She recommended that I stop with pediasure and start making my own mix of full-fat coconut milk (Silk makes a coconut milk, find it in the milk section) and part cow milk (wean him off slowly) with a few heaping teaspoons of hemp protein (I get it on Amazon.com in a 4 lb bag I believe) and I add sugar free chocolate syrup. I blend it in my "magic bullet" blender to make it smoother, but you can just shake it realllllly well. My son drinks this mid-day and I add his medicine to it. He thinks it is a chocolate shake and it really tastes good. :) You can also blend frozen fruit into it (then I would not use choc. syrup) if he will drink smoothies.

In the mornings I give him V8 fusion with his liquid multi vitamin in it.

I also did a "feeding therapy" group with my son during the summer which we pretty much just played with a variety of foods and made it fun. He reacts much calmer when we offer him food now, still usually says no but it is a step.

Good luck! Hope this helps. :)

My son loves rice milk w/ chocolate rice protein shakes. We call it chocolate milk. We like it because it doesn't make him bloated or irritate his tummy since we try to stay away from the milk/whey products. We get our rice protein at Vitamin Cottage or Sprouts. We just add a scoop to a sippy cup of rice milk and shake it up, but I'm sure it would work great in the blender with bananas or other fruit too.

Here's a really good one that you can change up if he gets tired of the flavors, or if he loves it, he can have more than one a day and he'd get some weight on. The secret is to give him protein and fat in the shake that doesn't taste as bad as the nutrition drinks (my son wont touch those)sold in cans.
Whey protein is one of the best muscle mass builders (muscle=weight), so if you can, buy him a can of powdered whey (available at GNC, or at Walmart in the supplement section), and use it in every shake.

Berry, Berry Protein Shake:

2 cups whole milk (or Flax milk, high in omega oils, also sold at Walmart)
1/2 tsp. vanilla
2 cups berries (strawberries, are less threatening in color than blueberries to start),or my son's favorites frozen cherries, or blueberries, or raspberries
1 whole ripe banana (fat and potassium)
2 scoops powdered whey protein powder
3 scoops ice cream (vanilla or strawberry) I use this when Ryan is convalesing from being sick and really needs alot of calories or use ice cubes to make a smoothie.

This basic smoothie/shake can be changed with the fruits of the season, or ones he really likes.
If you can't find the protein powder locally, you can order it online at amazon.com "Optimum Nutrician 100% Whey Gold Standard" is a good one, and only $19.97 with free shipping at certain times. Good luck and just keep playing with it.
I also suggest you use a special cup, and spoon with a fun straw for added fun!

You can use soy, I just discovered the flax milk at Walmart, and it has the additional omega3s I've been trying to get into Ryan's diet without having to buy $9.00 a pound salmon. lol He likes the taste better than soy, so he drinks more of it.
Ryan eats alot of different foods, but when he doesn't like something he wont budge. The list of alternative milks I tried before finding the flax milk he likes? Soy, coconut, and almond all in vanilla of chocolate flavors. I like that the flax milk feels like real milk in my mouth, and I can use it in all the ways I used milk before, just like you can the soy milk
Another suggestion...you could buy a popcicle mold and freeze these and give them to him as often as he'll eat them. I noticed he likes snickers, which means he likes peanuts...you could make banana peanut butter milkshakes, or popcicles and he would get a big boost of protein too.