Like other grains, Soy contains lectins and high levels of phytates. Soy is seems to have negative effects on so many functions such as thyroid & hormone levels (though I'm not sure how extracting the isoflavones would impact this). Some other good answers about Soy i.e. here

Before your surgery is it an option to do lots of cooking and stock up your freezer - with individual portions of meals you can defrost and reheat each day? Things like stews, soups and bone broths? Egg muffins would also last a few days in the fridge.

Making your own smoothies would be a better option than meal replacement drinks and take no time at all to prepare - just make sure you have some good fat sources in there too, perhaps coconut milk as a base, good quality raw eggs and things like green veggies/ berries

Read the Vegetarian Myth for info on soy! Just finished it yesterday. Very small amounts cause huge problems! You can probably find it at your local library. I wouldn't drink the shakes.

Why not make your own? 3 home-pasteurized eggs (boil egg for 45 seconds only-tx Dr. Eades), 1/2 c coconut milk, 1/2 c ice, 1 cup frz fresh strawberries or other berry, or, if you don't have hypoglycemic issues a very small banana with 2 tbl nut butter - blend in Vitamix or blender. I did raw eggs once (Nature's Promise Omega) in my shake and got salmonella-ouch! Will NEVER eat raw eggs again. Even though a local pastured egg MIGHT be fine, my experience was so aversive that I'll never try again! Lower abd pain for 24 hrs - felt like someone was pulling at all my organs with a hook!

What about tins of sardines, olives, cheese if you do it, a few nuts won't hurt, grapefurit, 1/2 apple, berries, pre-cut raw veggies or salad fixings fixed ahead of time for the first week and have some meats pre-cooked for your first 1-3 days home. I also make and freeze meatballs and then just nuke and add (home made sauce) or a good quality jarred marinara. You can pre-cook spaghetti squash, strain and freeze too. Make a meatloaf, cool, slice and freeze portions. Make egg/bacon cupcakes thingys and freeze. Chicken stew made ahead of time would be great for your first couple days home esp. if you have anesthesia. You won't feel like eating much your first 24 hrs. You could also make bone broth and freeze to take out mid week. That really keeps me for 4 hrs alone.

I keep meat babyfood on hand for when my dog gets sick. I also tell my puppy clients to have it on hand for their spay/neuter as most pups can only handle 2 oz of meat at a time every 2 hrs. (For those who like to be in the kitchen, I suggest boiling chicken breast and saving the broth.)

Have you tried whey protein shakes? Most of the issues with Paleo and milk is the sugar response from milk, but whey isolate in a low carb shake isn't going to boost your insulin levels. However, some folks are terribly sensitive to even whey protein, but it's a cheap and decent alternative if you're going the shake route.

If you're going to stay paleo and don't want to make your own you can find egg white shakes from most supplement shops and mark sisson from mark's daily apple has a paleo friendly protein shake as well. Just understand that the paleo option tends to be a bit pricier, but I've heard really good thing's about the protein powder from primal blueprint link text