Does insulin increase muscle growth?
Insulin is often called ‘the storage hormone’. It promotes the storage of carbohydrate and fat. But what is the effect of insulin on muscle protein metabolism?
Animal studies show that insulin can directly stimulate muscle protein synthesis (the process driving muscle adaptation). In addition, insulin increases blood flow and may thereby improve nutrient delivery to the muscle.
In this systematic review, we looked at all studies investigating the effect of insulin administration on muscle protein synthesis and in humans.
The impact of insulin on muscle protein synthesis appeared to be highly dependent on the context. We found that insulin does not stimulate muscle protein synthesis under physiologically relevant conditions, such as the fasted state or following a meal.
However, when supra-physiological (much higher than the body can produce) doses of insulin were administrated, muscle protein synthesis rates did increase further. However, this is of course not reflective of what happens in response to nutrition and can be very dangerous.
In contrast, insulin reduces muscle protein breakdown. However, you only need a little bit of insulin to maximize this effect.
Therefore, there is no need to ‘spike’ insulin to stimulate muscle growth.
Our systematic review:
https://www.ncbi.nlm.nih.gov/pubmed/25646407
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