When you hear people talk about fast and slow proteins, what the “fast and slow” is referring to is the absorption rate, or how quickly it gets to work in your body. In the case of protein powders, there are two that represent the fast and slow proteins, Whey and Casein. Whey is fast and Casein is slow. In knowing how these two proteins work, you can make a more informed decision as to which protein is right for you. Now for some science.
Proteins are absorbed in the small intestines and transported via the blood to different tissues of the body. These proteins have amino acids in them – essential amino acids. Essential amino acids cannot be produced by the body but are imperative to the body’s function. They effect everything from your bones to your brain. The problem with this is that amino acids are chains and aren’t always easily broken down. The gastric acid in the stomach and small intestines work on these amino acids to break them apart. Some are a lot harder to break apart and take a lot longer. The “fast” and “slow” description of proteins is in reference to how long one takes to break down in comparison to the other. An easily broken down protein is considered soluble or easily dissolved and, of course, the opposite is true of proteins that are harder to break down.
Whey is an example of a fast protein. Casein is an example of a slow protein. An easy way to explain this is a peanut. If you take a peanut and drop it in a beaker of acid. It will immediately be broken down by the acid. This time take a peanut still in the shell. Drop it in the acid. It takes longer for the acid to break through the shell to the inner meat and dissolve it. Whey is like the peanut with no shell and Casein is like the peanut with the shell. In the stomach and small intestines, the whey is very soluble and breaks apart easily. As a result, the whey protein gets dispersed to numerous tissues fast. Casein kind of gobs up in the stomach acid and thickens up due to the “outer shell” dissolving. Because it is harder to break down, it gets released slower and finds its way to the outer lying tissues at a much slower pace than Whey.
Once the whey protein gets through the digestion phase, its effects (like fullness and/or energy) last for only a few hours. This equates to a push of energy. When Casein makes it through digestion, it is a slower, steadier rate so its effects last longer. There is no push of energy, but a slow steady stream. A less pronounced effect than Whey. You feel fuller longer taking Casein but you get faster energy from Whey. This explains the “fast and slow” factor, but there is more.
Initially, besides the speed they are metabolized, whey and casein seem to have the same protein make up. They are VERY similar – both are complete proteins and both are soluble but there is a remaining factor that separates the two even further than their digestion speed. Whey supplies a higher amount of Leucine while Casein is higher in Glutamine. What difference does that make? In the short term, not much. But in the big picture, it can make a difference. Leucine directly effects muscle mass and building it up. Glutamine, however, builds the muscle mass but more as a repair process. So they both head straight away to the muscle tissue but perform two different tasks.
So now what? They both are proteins. They both have specific jobs. They both are excellent for your body. Which is better? The faster Whey or the slower Casein. There is no right or wrong answer. It really depends on the needs of your workout and what you prefer. Most athletes take protein powders for the fast energy and muscle building properties, which is the Whey protein powder. Some take Casein for a slower, longer energy. This would also follow the thinking that if your particular sport was a sport that needed a burst of energy, such as weightlifting/bodybuilding, you would benefit from the whey protein powder. If you participated in a sport that required longer lengths of energy, like long distance running, then casein protein powder would give a steadier stream of energy. Think of it as football players. Two players, same size and weight – one sprints the length of the field and scores. One runs short plays and over many plays makes it to score. They both score – they just take two different routes to the goal.
There are so many different thoughts and beliefs when it comes to protein powders and what is right and what is wrong. There really is no right or wrong – only what works for you. There are people who will swear on their mother’s life that Whey protein is the only protein that works. Then there are those who chant “longer is stronger” and have sold their souls to Casein protein powder. There are those who can’t decide and use both – whey before a workout and casein after. What works for one may not work for the other. It’s your body. You control what you put in it. It may take some time to see which works for your body. Just be consistent and only use 100% pure protein products. As always, anything but pure is a waste of time. Make sure you take the correct amount too.
So in the grand scheme of fast and slow proteins, there is no good or bad. There is no better or best. They both supply the proteins your body needs. They both will have an amazingly positive boost for your body. They both will give you energy. They both will build up your muscles. They both are essential to your body’s function. They both are complete proteins full of amino acids. They both are able to be broken down and used throughout the tissues of your body. They both are natural. It all boils down to a matter of speed.