> 3. Say soy protein powder (the type which can be mixed with water to create a shake that is used in some diet programs) is added to a smoothie. The person who drinks this smoothie is not interested in losing weight but in gaining it, but knows that while the protein powder may not help in gaining weight, it will add the soy protein which will help in other ways. Should this person look for something else to add to her smoothie instead?

The reason protein powder is used in diet and/or bodybuilding shakes has nothing to do with protein making you lose weight. As somebody else said here, if you eat more of any kind of food, all else being equal, you will gain weight.

Bodybuilders use high-protein diets to gain weight, because *in combination* with the exercise and lack of fats and sugars, it helps them to gain muscle. If you have more muscle, you will weigh more. Bodybuilding protein drinks tend to be a high-protein base with various other components such as chromium which may increase fat loss, and large amounts of the vitamins and minerals which may be needed or helpful to someone doing strenuous sports.

Slimmers also use high-protein diets because if you're not eating fats and sugars, uh, you're pretty much left with eating protein if you plan on staying alive. Depending on the brand and purpose of the product, there may not even be a whole lot of difference between protein powders sold for weight gain and protein powders sold for weight loss. A lot of the effect depends on how much exercise you do and whether it's weight training or aerobic.

So putting protein in your shake, whether it's soy or whey or egg or giant lumps of raw steak (now there's a great sounding drink) will not, in itself, make you either gain or lose muscle or fat. However, the mere fact that you're taking in more calories than you normally do will make you gain weight. And increasing protein is probably better for you than increasing fats and sugars.