Scientific Challenges on Theory of Fat Burning by Exercise - PMC

Hard exercise helps you lose belly fat not by simply melting the fat away, but by sending your food to rebuild tired muscles instead of storing it as fat.

Many people believe in fat burning, which is the idea that when you run fast, your body uses your fat like firewood to make energy. However, scientists found out that this is not actually what happens during a hard workout.

Instead, your body acts like a smart sharing system:

• Tired muscles need food: When you run super fast or lift heavy things, your muscles and lungs work very hard and get tired. They need building blocks from your food to fix themselves and grow bigger.
• Sharing the building blocks: After you eat, your body has lots of energy blocks called carbon and nitrogen.
• Muscles get first pick: Because your muscles worked so hard, your body sends most of these building blocks straight to your muscles to repair them, leaving nothing left over for your fat tissues.
• Fat shrinks away: Since the fat cells do not get any new building blocks to replace what they naturally lose every day, the fat slowly shrinks.

So, fast exercise helps you lose fat because it tricks your body into feeding your strong muscles instead of feeding your belly fat.