Hour by Hour. Here's what happens to your body when you fast.

Timeline – what happens to your body when you fast. 

8 – after 8 hours your body has used the last of its energy source from sugar. It switches to finding energy from your fat cells. 

12 - after 12 hours you’ve entered the metabolic state of ketosis, your body starts to break down fat and burn fat.

18 – by 18 hours you’ve switched to fat burning mode and you are generating significant ketones. These ketones signal body to ramp up stress-busting pathways which reduce inflammation.

24 – within 24 hours your cells are breaking down and getting rid of old components which are shown to be linked to Alzheimer’s and other diseases. 

48 – at this stage with little or no calories, carbs or protein the body’s growth hormone level is up 5 times as when you started. This hormone assists preserving lean muscle and reduce fat tissue accumulation.