Insulin is an ancient hormone that influences many processes in the body. Its main role is to manage circulating concentrations of nutrients (principally glucose and fatty acids, the body's two main fuels), keeping them within a fairly narrow range*. It does this by encouraging the transport of nutrients into cells from the circulation, and discouraging the export of nutrients out of storage sites, in response to an increase in circulating nutrients (glucose or fatty acids). It therefore operates a negative feedback loop that constrains circulating nutrient concentrations. It also has many other functions that are tissue-specific.
Insulin resistance is a state in which cells lose sensitivity to the effects of insulin, eventually leading to a diminished ability to control circulating nutrients (glucose and fatty acids). It is a major contributor to diabetes risk, and probably a contributor to the risk of cardiovascular disease, certain cancers and a number of other disorders.
Why is it important to manage the concentration of circulating nutrients to keep them within a narrow range? The answer to that question is the crux of this post.
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