Whey protein is quick to digest and provides all of the amino acids, the building blocks of protein, including essential amino acids that the body can't make itself. Whey protein makes its way into muscles most efficiently when taken immediately after a workout, ideally within 30 minutes, and when taken with carbohydrates. For fastest protein absorption, aim for a ratio of 1 gram of protein for every 2 to 4 grams of carbohydrates.
Casein protein is much slower to digest than whey, and leads to a lower, but more sustained increase in blood levels of amino acids. While it might seem that slow digesting proteins are inferior to those that get into the body more quickly, this isn't necessarily true. For example, taking casein at night can help sustain amino acid levels through the long fast that occurs during sleep. A type of casein found in protein powders, called micellar casein, is one of the slowest digesting proteins available.
Egg protein has a very high protein efficiency ratio (PER), which is one measure of how well our bodies can use any particular form of protein. Another reason people like it is the "Goldilocks factor"-it's not absorbed as fast as whey, but is absorbed faster than casein. Egg contains all amino acids, including essential amino acids.
Soy protein is a high-quality plant protein and provides all essential amino acids. It's prized by fitness enthusiasts because of its purported ability to boost nitric oxide levels in the body, which may improve blood flow. Although some men worry about soy's effects on testosterone and estrogen, the latest research solidly supports that soy does not increase estrogen levels or decrease testosterone levels in men. Soy protein isolate is faster and easier to digest, while soy concentrates contain some carbohydrates, which slow absorption into the body.
Rice protein is less likely than other proteins to create allergic reactions. While rice protein does not supply all essential amino acids, it does have one advantage: it contains a high proportion of arginine, an amino acid that can dilate blood vessels. This may, in turn, enhance blood flow to muscles.
Casein, egg, and soy are common allergens, so read labels carefully to make sure you are not purchasing a product that may trigger your food allergies.