system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does exercise actually reduce the risk of diabetes? And how does too much sugar in a diet cause a person with no diabetes to get the disease?
gpt
Type two diabetes is effectively caused by having a higher than normal blood glucose level for a prolonged period of time. 

When you eat, most carbohydrates are transformed into glucose and absorbed into the bloodstream. Simple sugars are digested and absorbed into the blood very quickly, causing large spikes in blood sugar. 

Insulin is released by the body to control blood glucose levels, and to enable cells to absorb and use glucose. Higher than normal glucose levels needs more insulin to control it. This ends up causing insulin ineffectiveness/resistance, which means tat your insulin is less able to control blood glucose levels. In response, the pancreas creates and releases higher and higher levels of insulin. This effectively makes the cells that produce glucose run out. Simple sugar is one if the things that causes this.

Exersize does two beneficial things. Firstly, it reduces your blood glucose. It helps you control it without relying on insulin. This reduces the strain on your insulin and can prevent insulin resistance and diabetes. Secondly, exersize makes your insulin more effective. Combined, this reduces the chances of getting diabetes.