Dairy-based whey and casein are the most popular sources of protein in muscle-building shakes and supplements sold across the country, according to exercise physiologist Dr. Helen Kollias. Whey is neutral enough to flavor easily, most healthy people are able to tolerate it well and -- perhaps most importantly -- the human body can digest it quickly. Experts have different opinions on exactly how rapidly whey can be absorbed, but it may be as fast as 15 minutes.
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Any type of whey protein powder is a relatively “fast-acting” protein, but not all have the same digestion and absorption rates. There are three types of whey sold as supplements: concentrate, isolate and hydrolysate. Concentrate is the least processed variety and contains the most lactose, fat and carbs. Isolate is further filtered to yield a powder with a higher percentage of pure protein. Hydrolysate is “predigested” whey broken down during processing to have a quicker digestion rate than nonhydrolyzed concentrates or isolates.
Different types of whey are digested at different rates. According to registered dietitian Jeffrey Volek, Ph.D., a high-quality whey protein supplement will begin to appear in your bloodstream about 15 minutes after you drink it. Jim Stoppani, Ph.D., who writes for “Muscle and Fitness” magazine, states in a 2014 article that whey delivers most of its amino acids to your muscles within 30 minutes. According to Kollias, it takes approximately 90 minutes after drinking a whey shake for amino acid levels in your bloodstream to peak, although they will begin to rise before an hour has passed.
As it turns out, the digestion rate for whey protein is not the same as its absorption rate. If you drink a shake that contains 50 or 60 grams of protein, for example, your body is unlikely to be able to absorb all of that protein at once. Any excess protein your body can’t metabolize becomes a waste product or is converted to body fat. According to Kollias, the maximum absorption rate for whey is about 8 to 10 grams of protein per hour. Thus, if you drink a shake with 50 grams of protein and it’s digested within an hour and a half, you’ll have only absorbed a maximum of about 15 grams of that protein.
Because of whey’s quick digestion rate but limited absorption rate, it can be beneficial to drink smaller amounts of it more frequently. Volek suggests taking in a total of 10 to 20 grams of protein, half before and half after your workout. Before you add any type of dietary supplement to your eating plan, get approval from your doctor.