Far and away the most popular supplemental protein used by athletes, bodybuilders and nearly anyone who supplements with protein is whey. Whey protein is derived from dairy and is a by-product of the cheese making process. When raw, whey is loaded with milk fat and lactose. In order to be a desirable protein, most of this fat and lactose must be removed. This can be done by either concentrating or isolating the whey to a pure form.
The elevator conversation version of the difference between concentrate and isolate is that isolate is better; always look for a pure isolate product if you can afford it. This is basically true, but things are never this black and white.
The whey concentration process filters the whey down, removing the lion's share of the fats and lactose, but not all of it. Further, the quality of the concentration process can vary quite a bit. Ultimately, concentrating protein results in a 70-85% concentration of pure protein. So in a 50 gram serving on whey concentrate, plan on getting 35-42 grams of pure protein, with the rest being lactose, fats, and other substrates of milk such as alpha lactoglobulins and lactoferrins, along with calcium, potassium and sodium.
On the other hand, the whey protein isolation process is much more thorough. It essentially separates the protein, almost in its entirety, from the raw whey, resulting in 90-94% pure protein. So in a 50 gram serving of whey protein isolate, plan on getting 45-47 grams of pure protein, with the remaining 3-5 grams being perhaps 1 gram of carbs and some calcium, potassium and sodium.
You could look at whey protein concentrate as spring water; as it is filtered, pure and healthy, but still contains all of the minerals etc. of natural water. Whereas whey protein isolate is like distilled water, as it is water in its purest form with virtually all other particles removed besides a hydrogen and oxygen molecule.
So what does this all mean to you? Essentially, both products are excellent proteins with very little fat, cholesterol and carbs. So, if you are looking for supplemental protein and keep a pretty healthy diet, you will be totally fine with a concentrate. The fat/cholesterol/carbs are minimal (but they do still exist) and concentrate also contains some other healthy milk ingredients like alpha lactoglobulins and lactoferrins. Most importantly, concentrated protein sells for about 25-35% less than does whey protein isolate. However, if you are on a very strict diet, preparing for a bodybuilding/figure show or trying to push your body to the absolute limit, whey protein isolate is they way to go.
There do exist differences from one concentrate to the next and one isolate to the next. Be sure to pick a high quality brand....Such as Isoflex and Isonatural pure whey protein isolates from Allmax Nutrition (www.allmaxnutrition.com). They also have a concentrate isolate blend, Allwhey, which is totally excellent and a top quality concentrate product that won't break the bank.