Hormones - Insulin Introduction

Hormones - Insulin Introduction Author: Technical Panel 20/06/2006

INSULIN

Insulin is a storage hormone secreted by the pancreas. Its primary purpose is to convert blood glucose into a form suitable for storage within the body. When kept at optimum levels blood glucose is used as fuel for the body and stored in muscle tissue for the synthesis of protein. Excess glucose is stored in the adipose tissue as glycerol 3-phosphate which is used for the synthesis of triglycerols (fat). It is therefore vital that optimum blood glucose levels are maintained if you want to build muscle and decrease body fat.

Blood glucose levels are controlled primarily by the liver. Following a meal high in carbohydrates blood glucose levels are dramatically increased. This stimulates the secretion of insulin by the pancreas. In response the glucose receptor sites in the liver are activated by the presence of glucose 6-phosphate which allows for the uptake of glucose into the muscle and adipose tissue where it is stored as glycogen. Once stored, blood glucose levels are decreased.

Insulin plays a directly anabolic role by facilitating the entry of amino acids from digested protein into muscle tissue. Amino acids are the building blocks of protein and are therefore vital for the building of muscle tissue. Insulin also stimulates the production of somatomedins by the liver which are muscle-growth factors, however, it is important to note that this involves insulin efficiency not insulin amount as the amount of insulin that can be utilised by the muscles is limited. Increasing insulin amount beyond an optimum level simply results in the storage of any excess as body fat. Chromium facilitates insulin function, therefore, in order to increase insulin efficiency sufficient chromium must be present in the body.

Insulin does not work alone in promoting muscle growth, it works in synergy with other hormones such as Growth Hormone. Most of the Growth Hormone produced by the body travels to the liver where it is destroyed, however, before it is destroyed it stimulates the production of Insulin-like Growth Factor I (IGF-I) which is used in the muscle cells to stimulate growth. Your level of IGF-I and your rate of muscle growth are therefore directly dependent on your insulin supply.

In order to maintain a steady stream of insulin without producing excess it is necessary to eat every few hours. Complex-carbohydrates are best as they take longer to be absorbed and ensure a slow trickle of glucose into the bloodstream preventing unnecessary peaks of excess which are ultimately stored as fat.

The exception to this rule is eating post-exercise. During intense training your muscle tissue loses glycogen, the stored form of glucose, rapidly. When blood glucose is decreased insulin production is also decreased and hence the anabolic effects of insulin are hindered. The amino acids necessary for protein synthesis and muscle growth can no longer be pushed into the muscle tissue and IGF-I cannot be synthesised. In this scenario the body requires a quick ingestion of simple sugar to raise blood glucose levels and stimulate the insulin drive. It is also possible to boost the body's insulin supply by including amino acids in your post exercise meal. Arginine and its precursor Ornithine increase insulin levels and levels of Glutamine are correlated with muscle protein synthesis.

More and more research is being done into the anabolic effects of this very powerful hormone. Understanding insulin and utilising it correctly to serve you in your purpose to gain muscle and lose bodyfat is essential. Please refer to the section on the insulin index for further information.



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