system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why does insulin sensitivity make people fat and why is too much sugar in blood bad?
gpt
Insulin sensitivity is good, insensitivity or resistance is bad. Insulin lets glucose into cells so that they can use it for energy. Without it, cells cannot make energy and thats obviously not good

Insulin resistance doesnt make people fat, becoming fat makes you insulin resistant. Its called metabolic syndrome and it can lead to things like high cholesterol, triglycerides and diabetes. 

Sugar in blood is bad because it can damage the blood vessels. This can lead to kidney failure (binds to blood vessels in kidneys) or the eye (blood vessels in the eye) and overall reduces the integrity of the blood vessel to cause things like heart attacks and strokes. It can also damage nerves and cause numbness in the feet.