BCAA Supplementation While Cutting Fat and Building Muscle
Do you need them?
When's the best time to take them?
What are they exactly?
What Are BCAA's?
BCAA's are constructed of three essential amino acids including leucine, isoleucine, and valine. While some BCAA products may add other amino acids or caffeine to their amino blends, the main base for BCAA products include these three essential amino acids.
Leucine is referred to as the main amino acid due to the numerous benefits leucine provides to the body. Leucine activates a protein within the body known as mTOR, which induces muscle protein synthesis. Many studies have shown that adding additional leucine into your diet can have a profound effect on increasing muscle protein synthesis.
Isoleucine and valine play their roles as well within the branched amino chain. Isoleucine also assists with protein synthesis and has a significant impact on increasing glucose uptake and the usage of glucose during exercise. Valine does not have quite the impact upon protein synthesis as leucine and isoleucine, but does assist with muscle metabolism and tissue repair. 
Do You Need BCAA's?The reasons leucine, isoleucine, and valine are so essential and so important to consume is because your body does not produce them naturally. Leucine, isoleucine, and valine must be consumed through whole foods such as chicken, beef or eggs, but are easier to consume and ensure the dosage through a BCAA supplement product.
BCAA's are available in both powder and capsule form, allowing you to control and know exactly how many grams of BCAA's you are getting each day.
When Do You Take BCAA's?BCAA's help support muscle growth and act as the fuel for your body when your energy tank starts reaching empty. During exercise, your body begins to fatigue and these essential amino acids begin to break down within your body.
While studies have shown that BCAA consumption prior to your workout can help increase protein synthesis and suppress muscle protein breakdown, consuming BCAA's during your workout can be beneficial as well when looking to add size and strength to your body.  During exercise, BCAA's are broken down thus allowing your body to use them as an energy source.
By keeping your body fueled with BCAA's during your workout, your body is less likely to reach an extreme level of fatigue by preventing a drop in your BCAA levels. And, if you are training in a fasted or low-carb state, BCAA's as an intra-workout supplement can help enhance fat utilization during exercise in a glycogen-depleted state. 
Should You Take BCAA's During a Cutting Phase?
One area of debate surrounding BCAA's recently has been whether you should continue to consume BCAA's during a "cutting" phase. A cutting phase is most commonly associated with bodybuilders, physique athletes, or fitness models that "cut" down to a specific weight and body fat percentage for a bodybuilding show or photo shoot.
Some fitness experts and professionals believe an individual should stop taking BCAA's during a cutting phase because it may inhibit fat burning and fat loss, which is the main goal during a cutting phase. On the other hand, many believe you should continue to have a proper intake of BCAA's during a cutting phase as it can assist maintain and build muscle during a time when your calories are reduced and your body is in a caloric deficit.
A recent study published in the Journal of the International Society of Sports Nutrition (2016) looked at determining the effectiveness of BCAA's in conjunction with heavy resistance training and a calorie restricted "cut" diet. An energy deficient diet is normally associated with losses in lean mass and decreased performance, so this study set out to prove just how effective BCAA consumption can be for someone in a cutting phase.
In this study, seventeen males who were experienced with resistance training were put on a low carbohydrate, calorically restricted diet and given either a BCAA product or a Powerade drink as the placebo. These subjects were instructed to not take any other supplements except those provided by the research team.
After 8 weeks of training, the group of individuals who was receiving the BCAA supplement showed that they maintained lean muscle mass, while making significant strength improvements in their one rep max squat and one rep max bench press.
BCAA's are essential for building and maintaining muscle whether you are in a cutting or bulking phase and can have a significant on improving your performance and energy levels when consumed as a pre-workout or intra-workout supplement.
References1) Examine.com. 9 February 2016.
2) Nosaka, K., Sacco, P., & Mawatari, K. (2006). Effects of amino acid supplementation on muscle soreness and damage. International Journal of Sport Nutrition and Exercise Metabolism, 16(6), 620.
3) Shimomura, Y., Murakami, T., Nakai, N., Nagasaki, M., & Harris, R. A. (2004). Exercise promotes BCAA catabolism: effects of BCAA supplementation on skeletal muscle during exercise. The Journal of Nutrition, 134(6), 1583S-1587S.
4) Dudgeon, Wesley David, Elizabeth Page Kelley, and Timothy Paul Scheett. ?In a Single-Blind, Matched Group Design: Branched-Chain Amino Acid Supplementation and Resistance Training Maintains Lean Body Mass during a Caloric Restricted Diet.? Journal of the International Society of Sports Nutrition 13 (2016): 1.