Our systematic review: 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 growth) (1). In addition, insulin increases blood flow and may thereby improve nutrient delivery to the muscle (2).

In the current systematic review, we looked all studies investigating muscle protein synthesis and insulin administration 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.

In other words, there is no need to ‘spike’ insulin to stimulate muscle growth.

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 conclusion, normal levels of insulin do not increase muscle protein synthesis. Only very high doses of insulin (e.g. injection) can further increase muscle protein synthesis.

Our systematic review:

https://www.ncbi.nlm.nih.gov/pubmed/25646407



This was the last infographic in the hormone series.

Click here to go back to the infographic index.

