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science nutrition blog

 By Steve Blechman


Branched-chain amino acids (BCAAs), or leucine, are best taken after exercise. Leucine, isoleucine and valine are called branched-chain amino acids (BCAAs) and they are essential amino acids, which means they must be consumed in the diet. BCAAs are involved in protein synthesis, tissue repair, signaling a biochemical pathway essential for muscle protein synthesis (i.e., mTOR) and blood sugar control. A meta-analysis that combined the results of seven studies showed that BCAA supplements are best taken after exercise, not before or during exercise (intra-workout). The studies revealed that BCAAs taken during exercise are “not effective on muscle soreness at follow-up time,” the researchers wrote.

Leucine consumption before your workout promotes sluggishness and fatigue. Recent research has shown that leucine competitively inhibits the dopamine precursor tyrosine into the brain and reduces dopamine levels. Dopamine and noradrenaline are the “flight-or-fight” hormones that allow the body to perform at higher levels than normal. Increasing dopamine reduces fatigue and increases mental arousal, focus, confidence and greater levels of motivation. Pre-workout leucine and BCAA consumption is not the best for optimal muscular performance.

According to the meta-analysis, when BCAAs are taken after exercise, they reduce post-exercise muscle soreness and creatine kinase— a marker of muscle damage— better than rest alone.

BCAAs promote recovery by stimulating the mTOR pathway to increase protein synthesis to repair injured tissue. Leucine, one of the BCAAs, is the most important chemical that turns on the mTOR pathway, so it is likely that consuming leucine after exercise would be more effective (and cheaper) than consuming BCAAs. The addition of isoleucine and valine may hinder the benefits of leucine due to competition for transport into muscle cells. The BCAAs share the same active transport system into cells and muscle cells. Indeed, isoleucine and valine have been shown to inhibit absorption of leucine. In the March 2018 issue of the International Journal of Sports Nutrition and Exercise Metabolism, it was reported that men fed 6 grams of whey protein supplemented with leucine, isoleucine and valine observed less protein synthesis than whey protein supplemented with just leucine. Also, research has shown that valine can cause insulin resistance in muscle, which is detrimental to muscle growth and enhances the accumulation of body fat. Recent research has also found that valine is associated with higher risk of hypertension.

Benefits of leucine:

- Leucine is the key anabolic trigger to protein synthesis.

- Increase in muscle protein synthesis are dependent on leucine concentration.

- 5 grams of leucine can increase the anabolic effects of protein synthesis when eating less protein, which is ideal on a ketogenic diet.

- Research has shown 6.25 grams of whey protein with 5 grams of leucine is equivalent to at least 25 grams of whey protein.

- Anabolic resistance in people over 40 can be overcome by consuming greater quantities of leucine.

- Leucine and not total protein content of a supplement is the primary determinant of muscle protein anabolic responses in healthy older people.

- Research has shown that pure leucine is more anabolic than protein in food!

- Leucine is the key amino acid for enhancing mTOR pathway that regulates cell growth and protein synthesis.

- Leucine has many benefits: powering muscle growth, preventing muscle loss especially during low-calorie, low-carb or ketogenic diets.

For best results as an anabolic trigger, take 5 grams of leucine (on an empty stomach) 15-30 minutes before a post-workout meal. By taking pure leucine on an empty stomach, you will get a better spike in blood levels than if you take leucine with food, because food can slow leucine’s absorption. When leucine is taken on an empty stomach, it’s a powerful metabolic switch that turns on protein synthesis. Leucine increases mTOR activity for several hours after training. When leucine is taken after resistance exercise and before a post-workout protein-containing meal rich in essential amino acids, it triggers greater protein synthesis for improved recovery and greater gains.



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