Does ingesting carbs after a workout build more muscle when added to protein? by Jerry Brainum

In recent years a popular sports nutrition concept has been that of nutrient timing. This concept suggests that when you consume certain nutrients in proximity to a workout can alter the results you get in terms of added muscle mass and strength. This is most often related to ingesting a fast-acting protein source, such as whey, with a high glycemic index carbohydrate, or a carbohydrate source that is quickly digested and absorbed. The principle behind this is that a rapidly absorbed protein such as whey, or even amino acids, will promote a more efficient  level of muscle protein synthesis, the cornerstone of muscular hypertrophy gains. The carbohydrates enter the picture because carbs are considered the most potent nutrient stimulator of insulin. While insulin has several functions in the body, in this sense a greater insulin release is sought because the extra insulin produced following a workout is thought to work in concert with essential amino acids, especially the branched-chain amino acid, leucine, to promote a greater level of muscle protein synthesis compared to consuming just protein alone.
    While it makes sense, this notion of adding a simple carb to a fast-acting protein source is theoretical.Some studies show a definite effect when protein is combined with carbs, while others show little or no effect. Indeed, recent studies suggest that consuming the correct amount of essential amino acids following a workout (about 8-10 grams, obtainable from 20-25 grams of whey protein) maximally promotes the muscle protein synthesis process alone, and added carbs do not add to this process.
    A lot of the confusion concerning the utility of a post-workout protein/carb drink accrues from a lack of understanding about insulin. Insulin is more related to a prevention of muscle protein breakdown, rather than simulating muscle protein synthesis. This, however, is an important consideration when you realize that muscle growth is the result of a balance between muscle protein synthesis and muscle protein breakdown, with growth featuring a greater activity of muscle protein synthesis. But blunting muscle protein breakdown pushes the metabolic scale towards more anabolic effects in muscle by favoring muscle protein synthesis. In that respect, insulin does help build muscle. The mistake often made about insulin is in relation to how much is required to affect muscle anabolic effects.
   It turns out that only slight elevations of insulin above basal levels are all that's required to blunt muscle catabolic effects. Just consuming protein alone is enough to elicit a release of insulin that is sufficient to interact with the ingested amino acids in promoting muscle protein synthesis. Leucine alone is known to promote the release of insulin. This explains the recent studies showing that protein alone is enough to boost muscle protein synthesis following training. Indeed, one study showed that boosting insulin levels 30-times above fasting level did not further boost muscle protein synthesis if blood levels of amino acids were high. Just consuming protein alone, especially whey, which is rich in leucine, is enough to boost insulin levels 2-3-fold above resting levels. This level of insulin alone is enough to provide the anti-catabolic effects of insulin following exercise. Other studies show that adding 30 or 90 grams of carbs to 20 grams of protein does not boost muscle protein synthesis to a greater degree, despite the fact that 90 grams of carbs promotes a greater insulin release compared to 30 grams. The level of insulin release required to boost muscle protein synthesis beyond this level can only be achieved injecting insulin, which would allow superphysiological levels of insulin to exist in the blood, far higher levels than can ever be reached through ingesting any amount of carbohydrates.
     But there are other reasons to add fast-acting carbs after a workout, even if it doesn't affect muscle protein synthesis. Carbs are still the best way to replenish depleted muscle glycogen levels. Glycogen repletion is required for complete muscle repair, and also serves as the primary energy source for anaerobic workouts such as occurs in bodybuilding. The enzymes that convert ingested carbs into glycogen are primed following training, and it's advisable to take advantage of this by consuming carbs within 2 hours following training. It fact, the timing for carb intake after training is even more critical than it is for protein intake. The muscle protein synthesis process continues for 24-48 hours following training. But the heightened glycogen-replenishing enzymes only last for 2 hours after a workout.In addition, the combination of protein and carbs will blunt cortisol release, as well as lower levels of AMPK, both of which interfere with muscle protein synthesis after training.
     

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