What's leucine?

Well, leucine is an essential amino acid and is a member of the branched chained amino acid family that also includes isoleucine and valine. There are a total of nine essential amino acids that the body can't make and must get from eating foods high in dietary protein. And once consumed digestive enzymes breakdown proteins into amino acids so they can be absorbed. Once absorbed amino acids travel to the liver and the liver then can determine whether or not amino acids are needed to make new body proteins (like muscle tissue), converted to glucose for needed energy or if not needed by the body converted to fat and stored for later use.

However, leucine is unique in that once absorbed it travels directly to muscle tissue where it acts as a signal for protein synthesis. How does it signal protein synthesis? Well, without getting too technical, leucine activates a special component of a muscle building metabolic pathway, called mTOR. Try to think of mTOR as the amino acid sensor in cells and know that it is sensitive to the presence of leucine. As leucine concentrations increase in muscle cells, mTOR knows there is sufficient protein available to make new muscle protein. Another way to better understand this process is with an analogy. You want build a brand new home and mTOR is the contracting company you hired to do the job. Your new home is like the protein your body is trying to make, the machines (bulldozers, cranes etc) you use to make the building are components of the protein synthesis pathway and leucine is the cash you need to make the project work. When enough cash is available (increased leucine concentrations in muscle tissue) the contracting company (mTOR) can not only start building your new home (new muscle protein) but can also purchase more machines (increased muscle building components) to increase the capacity and speed at which they construct your new home (the muscle protein being made).

So now that you understand how leucine works to signal muscle protein synthesis - let's discuss why this is important for weight loss. Well, to start it's important to know that your body's muscle like many other tissues of the body, it is constantly being broken down and built back up again. When the rate of muscle breakdown is equal to the rate of muscle building, the result is maintenance of muscle protein tissue. However, the problem is that when you restrict calories in attempt to lose weight, your body still needs to supply energy for every day functions (the beating of your heart, breathing, etc.) and to accomplish that it will used stored energy in your muscles and liver, start to break down stored body fat but it also breaks down muscle and other body proteins to amino acids, which can be further metabolized to produce energy.

However, you don't want to break down your muscle tissue for energy because muscle is metabolically active tissue. It burns calories. So where leucine helps is by stimulating muscle protein synthesis, thereby offsetting the breakdown that naturally occurs when you cut calories to lose weight. The payoff - leucine helps your body preserve muscle mass while you lose weight from fat. In turn holding on your muscle mass while you lose weight also helps protect you from the drop in metabolism that typically occurs in most diets. And keeping your metabolic rate from dropping is key to successful long term weight management.

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