How is it decided what type of food we want to eat?
I'm no biologist but here are two answers to your multidimensional question. "How is it decided what type of food we want to eat?"
There is new research into neuroscience and microbiological science about a phenomena where bacteria in our gut that produce vitamins and digest things that we cannot digest, contribute to the choices we make for our diet. Don't ask me how, but from my understanding they must somehow communicate with the brain to release dopamine while stimulating neurons responsible for choosing a certain food to crave. "Is there something that measures for example what is level of glucose or amino-acids or some fats in blood...?" Well yes actually, let's take the pancreas for example. It knows when blood sugar is high from digested materials and will begin to produce insulin. I won't go much further because already there is a response based on the detection of sugars. Your entire digestive tract is based on these detective processes in order to appropriately digest and react to digested material. Are there processes that tell your brain what to eat next? Well besides the bacteria, there are plenty of hormones produced by your gastrointestinal tract such as Ghrelin which is the most common "hunger hormone" and is responsible for homeostasis aka energy regulation/distribution throughout your body.

It's better not to ask how but to ask why when researching topics similar to this, the how is almost always provided. I'm not entirely sure how those hormones communicate with the brain, my knowledge of the brain is less biochemical and more neurological (e.g. neuron formation).