As
@Martin.A said - insulin resistance isn't fully understood, though there are known steps that may help address it.
Generally speaking, the most common theory I've read is that insulin resistance is caused by excessive ectopic fat. This is fat stored in the cells of tissues other than adipose tissue, which is where the dedicated fat-storage cells are. Fat enters these cells from the blood in the form of triglycerides or free fatty acids. The three primary suspects for the kind of insulin resistance that is associated with T2 diabetes are liver tissue, muscle tissue, and adipose tissue.
Reducing insulin resistance in the liver is quite straightforward for many people, if they are overweight - losing a substantial amount amount of body fat will empty out some of the fat in the liver. The liver is constantly pumping out fat in the form of triglycerides. Losing weight leads to less fat going in than coming out, reducing the amount of fat stored in that organ, which may reduce the level of insulin resistance in that tissue and perhaps lead to lower fasting blood glucose levels. Reducing liver fat levels may also lower blood triglyceride levels, which may lead to lower levels of ectopic fat stored throughout the body.
Ectopic fat stored in muscle tissue can be reduced through moderate exercise. Muscle will burn primarily fat if the exercise is moderate/aerobic, like walking, or primarily glucose if the exercise is intense, like sprinting or lifting weights. The effect is short-lived as muscle will soak up triglycerides from the blood and replenish stores, though exercise has been shown to reduce insulin resistance in muscle tissue somewhat for a couple of days after exercise.
Insulin resistance in adipose tissue (fat cells) is the least well understood as far as I can make out. One theory I've read is that if fat cells grow too large too fast they become inflamed, insulin resistant, and start to 'leak' free fatty acids into the blood. If this happens on a large enough scale the levels of free fatty acids in the bloodstream rises, leading to more inflammation in fat cells as they soak up the FFAs, leading to more 'leaks' and so on. The only suggested solution to this, if it's true, is weight loss, to empty out inflamed fat cells, and time.
Other theories I've read include:
- Fat cells become inflamed and insulin resistance if they store too much omega 6 oils, which allegedly prevents the expansion of fat cell size in some fashion.
- Insulin resistance in muscle tissue is caused by too much insulin in the blood - insulin cause insulin resistance, maybe.
- Insulin resistance is caused by too much cholesterol stored in cells. Reduce cholesterol and insulin resistance is reduced, perhaps.
- Insulin resistance is caused by inflammation in general - a catch-all for all manner of causes from smoking to toothache
The fact that there are so many theories tells you how little understood the mechanisms are. All we can do at present is lose weight, if we have weight to lose, exercise, if we can, and handle the rest with diet and medication.
It is worth noting though that Metformin primarily inhibits glucose output from the liver, but is also thought to reduce insulin resistance, perhaps in muscle tissue.
