Protein shakes - whey vs. soy

There is some question that soy, in large quantities, can have varied negative effects on the body.  There is no evidence, however, that a serving or two of soy has any negative effect.  Soy protein is a complete protein, just like whey.  Unless your planning on downing more than 2 soy protein shakes a day, its probably no big deal.  One decent article on the subject by some bodybuilder/nutritionists is here.

On the other hand, whey is typically much cheaper, and some argue that it has a great absorption rate than other forms of protein.  These claims, I think, are typically put forth by supplement companies and are largely unverified by science.

On the other hand STILL, there are several large studies (such as the infamous China Study) linking consumption of dairy products with cancer, especially in women.  Add to that the varied growth hormones and antibiotics that go in to cows, and whatever else they do to those poor animals, and who knows what winds up in your whey.  That is less of a concern with soy, not the least because soy companies are often targeted towards people who care about organic foods and such.  Bodybuilders and weight lifters, the primary consumers of whey protein powders, don't.

My opinion is that finding protein that is cheap and tastes good is probably much more important than the difference of whey vs. soy, beacuse if I miss my protein intake goal for the day because it tastes bad or is expensive, this will be much worse than any detriment soy might pose.  For these reasons, I always use whey, because its cheaper and tastes good.

Whey tends to be the fastest absorbed protein by the body.  Soy is described (though, like the previous poster, I am not sure this is clinically proven) as a medium-speed-digested protein.  Casein is described as the slowest, taking upwards of 8 hours to be absorbed by the digestive system because it is so densely bonded.

If you're looking for a pre-workout shake, choose whey and eat a slow digesting carb (wheat bread, brown rice, etc.)

For post-workout, choose whey and a fast protein, like Gatorade, white bread, white potato, etc.

For bedtime, choose soy or casein...these two proteins take longer to digest, effectively "feeding" your muscles while you sleep.  Cottage cheese is FILLED with casein...three tablespoons of it with a little bit of fish oil at night REALLY regenerates ripped up muscle tissue.