How do fats leave your body when you diet?

When you diet and lose weight, you lose body fat through a process called “lipolysis”. This is how your body breaks down stored fat and leaves your body. Many people think that fat is simply “burned” and disappears, but the story is a little more complicated. Here's an overview of exactly what's happening.

1. Fat storage and energy shortage

Body fat is stored in fat cells in the form of triglycerides. These are molecules made up of glycerol and three fatty acids. When you eat fewer calories than you burn (calorie deficit), your body switches to using stored fats as an energy source. This process begins with the breakdown of triglycerides.

2. Fat breakdown: lipolysis

In a state of calorie deficit, your body stimulates the breakdown of fat through the following steps:

1. Hormones activate fat breakdown
   • Hormones such as adrenaline and glucagon activate enzymes that break down triglycerides in your fat cells.
2. Release of fatty acids and glycerol
   • Triglycerides are broken down into:
     • Fatty acids , which are transported through your blood to cells that need energy (eg muscles).
     • Glycerol , which goes to the liver and is converted to glucose (for energy).

3. Energy production (fat burning)

The released fatty acids are used in the mitochondria (the energy factories of cells) to produce energy. This process is called beta oxidation :