Insulin Reduces Muscle Tissue Breakdown
by: Robbie Durand
About ten years ago, the late Dan Duchaine talked about the anabolic effects of insulin for bodybuilders in a issue of Muscle Media. In the past, most bodybuilders thought insulin was an “evil” hormone that promoted fat mass gain. Insulin not only promotes fat storage, but also regulates a wide array of cellular events that result in up-regulation of cellular nutrition. Dan was a proponent of insulin spiking after exercise, because insulin has an anabolic effect on nutrient uptake in cells through enhances in muscle glycogen uptake.
The working theory was that whey protein in combination with the insulin spiking actions of carbohydrates would accelerate anabolic activity after exercise. The gold standard for post exercise recovery was a whey protein shake with maltodextrins or vitargo post-exercise. The main proponents for carbohydrates post-exercise are: to initiate protein synthesis and to refill muscle glycogen stores.
The bodybuilding world was turned upside down in 2007 when researchers tested three groups of males who underwent resistance training and then either consumed a protein only post-workout drink, protein and low carbs, or protein and high carbs. Most people would have suspected that the whey and carbohydrate group would have had greater protein synthesis post-exercise, but that’s not what the researchers found.
The researchers amazingly found that co-ingestion of carbohydrate during recovery with protein did not further stimulate post-exercise muscle protein synthesis when ample protein is ingested. Since this study, researchers have discovered the amino acid leucine is very insulinogenic and the higher the leucine content, the greater the insulin response. Leucine ingestion results in a marked increase in circulating insulin concentrations at a minimum of two to threefold above fasting values.
I wrote an previous article last week titled “Carbo-Lies: Carbohydrates Don’t Affect Protein Synthesis” so I was very excited when I came across the latest research regarding insulin and protein synthesis published this month in Diabetologica titled, “Role of insulin in the regulation of human skeletal muscle protein synthesis and breakdown: a systematic review and meta-analysis.”
The researchers aimed to investigate the role of insulin in regulating human skeletal muscle metabolism in health and diabetes. The researchers conducted a systematic review and meta-analysis of published data that examined changes in skeletal muscle protein synthesis and/or muscle protein breakdown in response to insulin infusion. A total of 104 articles were examined in detail. Of these, 44 and 25 studies (including a total of 173 individuals) were included in the systematic review and meta-analysis, respectively.
In the overall estimate, insulin did not affect muscle protein synthesis, but significantly reduced muscle protein breakdown. An increase in muscle protein synthesis was observed when amino acids availability increased, but not when amino acids availability was reduced or unchanged. In individuals with diabetes and in the presence of maintained delivery of amino acids, there was a significant reduction in muscle protein synthesis in response to insulin. This study demonstrates the complex role of insulin in regulating skeletal muscle metabolism. Insulin appears to have a permissive role in muscle protein synthesis in the presence of elevated amino acids, and plays a clear role in reducing muscle protein breakdown independent of amino acid availability.
The really interesting aspect of this study is that it shows that insulin’s main actions are to prevent catabolism, or muscle tissue breakdown in muscle, which is a good thing. Insulin even without amino acids clearly reduced muscle tissue breakdown. So the use of carbohydrates post-exercise are great for the offseason bodybuilder who is looking to increase muscle mass or athletes that are training twice a day, which the extra carbs can enhance post-exercise recovery.
For the athlete that is dieting and counting calories, you can skip the carbs and get the carbohydrates from your diet, as carbs are not going to further enhance muscle protein synthesis as long as amino acid/leucine content is high. Therefore, using carbohydrates post-exercise should really depend on your goals (fat loss or muscle building) and training intensity.
Rene, Beelen Milou (2007) Co-ingestion of carbohydrate with protein does not further augment post-exercise muscle protein synthesis. Am J Physiol Endocrinology Metabolism.
Figueiredo Vandre, Cameron-Smith David (2013) Is carbohydrate needed to further stimulate muscle protein synthesis/hypertrophy following resistance exercise? The Journal of The International Society of Sports Nutrition.
Abdulla H, Smith K, Atherton PJ, Idris I. Role of insulin in the regulation of human skeletal muscle protein synthesis and breakdown: a systematic review and meta-analysis. Diabetologia. 2015 Sep 24.