Fact: Both rapidly and slowly digested proteins offer significant benefits to athletes.
Recent research has brought up the notion of "fast" and "slow" proteins.11 They are designated as such according to the rate at which they raise blood levels of amino acids after they are consumed. Whey protein for example is considered a fast protein and causes a rapid increase in amino acid levels. Casein on the other hand is considered a slow protein.
Both rapid and slow proteins offer benefits to someone trying to build muscle. Research has shown that proteins that enter the blood stream rapidly significantly increase protein synthesis. Proteins that enter the blood stream slowly have a pronounced effect on protein breakdown, significantly inhibiting it even at low quantities.
By using a combination of proteins that exhibit both fast and slow properties one should be able not only to jump-start protein uptake into muscle cells during a grueling workout, but also ensure that protein synthesis is jump started and that protein break down is kept at a minimum during the hours following their workout. Take the fast protein before training, and a slow protein after for maximum anabolic effect.
In summary, it is a mistake to say that a "fast" protein is better than a "slow" protein. Both types of protein should be used in strategic fashion to alter protein metabolism in favor of net protein deposition (i.e. muscle growth).
Myth #4: A protein must have added peptides of specific molecular weights to effectively build muscle.
Fact: The bodyıs digestive tract makes its own variable molecular weight peptides from the whole proteins you eat.
As soon as protein hits the stomach it is attacked by powerful stomach acids. This acid, along with an enzyme called pepsin, serves to change or denature the proteins structure preparing it for further digestion in the small intestine. In the small intestine several other enzymes work to break down the protein into various molecular weight peptides and free amino acids. Each enzyme acts on a specific part of the amino acid chain cleaving it in the appropriate place. Whether youıve just eaten a steak, scrambled eggs or a glass of whey protein, the end result of digestion is the same, a full spectrum of molecular weight peptides and a moderate amount of free amino acids perfectly suited for absorption into the body.
The small intestine has special transporters which actively pull peptides across the brush border membrane and into intestinal cells. All the various peptide transporters have yet to be clearly identified. As a result of these transporters, peptides can be actively absorbed faster than free amino acids. Within intestinal cells, peptides are further broken down into individual amino acids by enzymes called protease (prote = protein, ase = to split or cleave). It has been shown that a very small percent of digested peptides can enter the blood stream by squeezing between intestinal cells. Even though some peptides make it into the blood stream intact, they are quickly broken down by proteases on the surface of liver and muscle cells. If by some small chance peptides actually make it all the way into these cells, they are rapidly broken down by proteases within the cell.
So you see, all this talk about adding various molecular weight peptides simply means that they predigested an already easily digestible protein. This simply adds to the expense of manufacturing the protein. The added cost, of course, is passed on to the consumer.
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