My eight-week program (Dr. Weil's Optimum Health Plan) encourages the use of soy foods as an excellent source of protein and as substitutes for animal foods, many of which are loaded with unhealthy saturated fats. In addition to the protein they provide, soy foods also contain healthy fat and isoflavones - unusual compounds that may offer significant protection against cancer (particularly hormonally driven malignancies such as breast and prostate cancers).
Whey is one of two dairy proteins. The other is casein, which can irritate the immune system and stimulate mucus production, worsening allergy symptoms. This reaction to casein is why milk consumption is associated with recurrent childhood ear infections, eczema, chronic bronchitis, asthma and sinus conditions. People who have autoimmune diseases or digestive problems may find that their symptoms improve when they eliminate milk and milk products.
Whey protein constitutes about 20 percent of total milk protein (the rest being casein) and is separated out from casein and increasingly isolated to make the various whey protein products now on the market (everything from powders to various drinks and protein bars). If you're lactose intolerant - that is, if you develop digestive symptoms after eating dairy products - you may or may not have problems with whey protein products depending on the amount of lactose they contain. And if you're allergic to milk protein, it is important to know whether the troublemaker is casein or whey before using whey protein products.
My feeling is that if you have an individual preference for whey protein and suffer no ill effects from its use, there's no reason why you shouldn't continue with it. You don't say whether you're using whey as a protein supplement or substitute. As a rule, I discourage use of protein supplements of any kind (including soy) because most of us eat too much protein anyway, even if we work out with weights. Incorporating soy protein into the diet as a substitute for animal protein remains a healthy change I would like to see more people make.
Andrew Weil, M.D.