Why is insulin sensitivity important?
Insulin sensitivity is a term that is often used but even more often misunderstood. In order to understand insulin sensitivity, we need to have a little crash course on what insulin is, why insulin is important and why we need to consider how to look after our insulin sensitivity in order to remain healthy and improve recovery and performance.
After eating a meal containing carbohydrates, digestion turns these into glucose molecules which are absorbed from the small intestine into the bloodstream. This raises blood glucose levels. When the pancreas detects the increase in blood glucose levels causes the release of insulin which acts as a transpoter to shuttle gluose into muscle tissue and liver. Normally, the amount of insulin released is proportionate to the amount of carbohydrate in a meal allowing the glucose to be taken up into the cells.
The issue comes when insulin sensitivity is poor this leads to not enough insulin being released
In some circumstances, insulin does not get the correct cellular response. Insulin binds to our cells, signalling internal transporters to come to the surface of the cell to allow glucose and amino acids to enter the cell. Under normal circumstances, this takes place quickly and effectively, but if our insulin sensitivity is poor then these transporters do not come to the surface of the cell at the rate we would expect when signalled by insulin and glucose transport into the cell is impaired.
Why is this problematic?
Well if insulin sensitivity becomes severely impaired this leads to insulin resistance, this is a key feature of type 2 diabetes. In this diseased state glucose and amino acids cannot be taken up into many of the body’s cells and this can have serious health implications. Even in those who are not towards the insulin resistance end of the spectrum, poor insulin sensitivity will lead to excessive amounts of insulin released relative to the amount of carbohydrate eaten as the pancreas keeps detecting elevated blood glucose levels and producing more and more insulin until eventually glucose is taken up into cells.
Although insulin release at the appropriate amount at the appropriate time is essential for nutrient uptake, excessive and sustained insulin production can prevent the breakdown of body fat for energy, leading to more rapid weight gain which in turn leads to even worse insulin sensitivity… and if this is not controlled can lead to type two diabetes.
This impairment of glucose and amino acid uptake has obvious implications for those who train; having the potential to impair recovery and growth. It is one of the key reasons why those on a bulking diet should not go too high with their body-fat levels, as it could actually impair muscle growth.
Although insulin and carbohydrate are intrinsically linked, that is not to say that a high carbohydrate diet is a causal factor of poor insulin sensitivity. Insulin sensitivity is affected by the build-up of fat inside cells which impairs signalling, so the cause of poor sensitivity should be considered a result of increased body fat, regardless if those extra calories come from carbohydrates or fats… both these nutrients in excess have been associated with reduced insulin sensitivity and insulin resistance.
How to improve insulin sensitivity
To improve insulin sensitivity it might come as no surprise that the main way to do this is to lose weight (if you are overweight), or if you are within normal body fat ranges to not let yourself get out of shape. Although it might seem logical to reduce carbohydrates to improve insulin sensitivity as part of a fat loss program, various diets have shown that any diet that causes fat loss will improve insulin sensitivity, even those that include carbohydrate.
General guidelines suggest keeping carbohydrates in the diet at a moderate or low level as a sensible option to improve insulin sensitivity as part of a fat loss program, but this is still debated in the academic community.
Exercise has also been shown to improve insulin sensitivity and resistance training, in particular, is an effective tool to do this as it stimulates the transporters of glucose to the cell surface without the need for insulin. This is one of the reasons why it is suggested that refuelling after training with higher GI carbohydrates/sugars is beneficial as nutrient uptake into the cells is more efficient, leading to improved recovery with a smaller demand for insulin secretion. This is beneficial for all those who train but highlights the importance of exercise in helping to restore insulin sensitivity and reduce insulin load in those who are overweight and/or living with type two diabetes.
Is there anything else we can do to promote better insulin sensitivity? If you are already lean then the chances are your insulin sensitivity will be about as good as it’s going to get, however there is some suggestion that various supplements might be able to optimise our insulin sensitivity even further allowing for more rapid nutrient uptake, potentially leading to more muscle growth, faster refuelling and glycogen synthesis whilst limiting fat gain.