Hopefully my previous answer will help you.  Unless you can sustain nuclear reactions in your gut, you can&#x27;t extract more energy from the food.  It is not possible.  You can easily extract less, though.<p>The calculations are simple because that&#x27;s how they were designed to work.  Going the other way (gaining weight) is actually where it is problematic (because not all of the food value is used -- although bodies are remarkably efficient).