What Is Leucine?
Leucine is an amino acid that is regularly taken as a supplement. It is essential to the body, meaning that it cannot be produced and is needed to survive. Hence, leucine must be provided through food intake or supplements.
Leucine is a branched chain amino acid (BCAA). The other two BCAAs are valine and isoleucine, with leucine the most promising of the three when used as a body building supplement.
Leucine increases energy and protein (therefore, muscle) production, which is a clear indication of its use as a bodybuilding supplement .
Similarly to many other amino acids, leucine is found in many foods that are high in protein. Examples include meats (such as fish, chicken, and turkey), dairy products (such as yogurt and cheese), and soybeans. Other foods like eggs, nuts, seeds, and fruit also contain leucine, but not to a lesser extent.
Leucine can be classified in:
L-leucine is the natural version of the amino acid, is found in the proteins of the body, and is the main form used as a supplement.
D-leucine is the mirror image of L-leucine, which is created in the laboratory and is also used as a supplement.
Health Benefits of Leucine
1) Leucine Is Used to Increase Energy Production
For the first 45 minutes, leucine supplementation increases energy production, but afterward, it produces a decrease in energy (most likely due to the restriction of pyruvate breakdown) .
Leucine Increases Energy
Leucine breakdown produces two molecules that are used to obtain energy: acetyl-CoA and acetoacetate .
In rats, leucine also serves as a precursor to different fats (fatty acids, nonsaponifiable fats, and sterols) that are later broken down to produce energy .
Fasting leads to increased levels of leucine in the blood and increased activity of enzymes that convert leucine into ketone bodies and used for energy .
Patients with deficiencies in the molecule that breaks down leucine into acetyl-CoA and acetoacetate (3-Hydroxy-3-methylglutaryl-CoA lyase) develop acidosis (low blood pH) and hypoglycemia (low blood glucose) .
On the other hand, in rats, leucine increases blood levels of insulin, which causes glucose uptake by the cells and ultimately energy production. Together,leucine and glucose induced a 4.5-fold increase in insulin (compared to 2.4-fold by glucose alone). Therefore, leucine plays a key role in maintaining glucose levels and producing energy .
But, Leucine Also Decreases Energy
Even though leucine increases insulin, which usually increases glucose uptake, leucine can also block glucose uptake.
Fasting increases blood levels of branched chain amino acids (BCAAs) such as leucine. A study found that fasted animals with increased leucine concentrations did not uptake as much glucose as non-fasted animals thereby reducing energy production .
Leucine blocks pyruvate (a molecule that glucose is converted to produce energy) breakdown so that the glucose can’t be used for energy.
This process of restricting pyruvate breakdown may explain why glucose uptake and energy production in the muscle of rats decreases after approximately 45 minutes .
In people that fasted, leucine supplements also reduced energy production because it inhibited the insulin-mediated glucose uptake by the muscles .
Leucine supplementation increases blood insulin levels, which boosts the uptake of glucose in the muscles. However, leucine decreased the insulin-mediated glucose utilization by 50 to 83% in fasted rats .
The inhibitory effect of leucine on energy production causes problems when it’s supplemented to increase energy. Therefore, it is advised that bodybuilders consume a meal prior to workouts. Otherwise, the supplementation could actually be hindering the workout.
Because of the inhibitory effect that leucine has on insulin-mediated glucose uptake, people with diabetes and those taking insulin should stay away from or not fast before leucine supplementation. This could possibly cause diabetic shock due to low levels of insulin and glucose.