Insulin, a hormone produced by the pancreas, is responsible for maintaining balance between macronutrients, which include sugars, protein and fats. Insulin controls glucose from meals, makes the tissues absorb this sugar and draw energy from it. If there is too much glucose, insulin "makes" the liver accumulate excess. In addition, insulin inhibits the breakdown of fats in adipose tissue.
It is primarily talked about improper nutrition - a diet high in sugars and fats, and lack of exercise. In 50% of patients genes play a role.
The precise diagnostic method (hyperinsulin euglycemic clamp, HEC) is expensive and time consuming, it is used only for scientific purposes. The popular method, which is based on measuring fasting and glucose and insulin levels, is really low.
First of all, insulin levels are very variable, including from how much time has passed since the last meal; secondly, laboratories use different methods for determining concentrations, and thirdly, there are no values to which the results could be referred, the so-called reference values.
So is there any reliable indicator of insulin resistance?
Many researchers mark equality between obesity and insulin resistance. If we want to rely on blood tests, it is worth looking at the values of: triglycerides and HDL ("healthy cholesterol"). Their ratio should not exceed 2.0. It is also worth making the usual sugar curve, i.e. fasting blood glucose and 75 hours of glucose after drinking. 
Studies have shown that the diet's effectiveness in preventing the transition from insulin resistance to type II diabetes is 58 to 71%. What diet should you choose? It must meet several conditions, its features are:
These criteria are met by: the Mediterranean diet, DASH and flexitarian. Contrary to some reports, a large 2015 study found that alcohol should be avoided.
The best results will be obtained by combining diet with regular physical exertion. It doesn't have to be everyday. All you need is 5 days a week after about half an hour of moderate exercise.
If diet and exercise have no effect, the doctor reaches for the weapon in the form of a drug - for metformin. Metformin sensitizes tissues to insulin, has anti-inflammatory properties (prevents the formation of tumors), and reduces appetite.
This drug is particularly helpful in patients with second degree obesity and in patients with polycystic ovary syndrome. Keep in mind that metformin is just an addition to diet and exercise.