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What is better — free-form leucine vs. leucine naturally found in whey

About 25 grams of whey protein contains about 3 grams of leucine, the amount that has been shown to produce maximal rates of muscle protein synthesis. Since leucine, a branched-chain amino acid, is a potent regulator of muscle protein synthesis, it might be possible to achieve similar results with less whey protein by adding additional leucine.

Researchers had subjects ingest either 25 grams of whey protein isolate alone or 6.25 grams of whey with 3 grams of added leucine (the same amount found in 25 grams of whey) after rest and again after exercise. Compared to fasting, rates of muscle protein synthesis up to 5 hours after the feedings of either whey or whey plus leucine were significantly increased but were similar between both test groups. However, when comparing the groups 3 to 5 hours after resistance exercise, the whey-only group resulted in nearly a two-fold greater increase in muscle protein synthesis.

The implications of these findings are that adding extra leucine to smaller amounts of whey can provide benefits similar to larger amounts of whey during rest (non-exercising conditions), but that 25 grams of whey alone provide a more sustained increase in muscle protein synthesis after resistance exercise.

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