Your brain has little slots called receptors (in this case they are called CB1 receptors) . Your brain uses lipids that can bind to the cb1 receptors causing you to feel hungry. THC found in weed binds to the CB1 receptors in your brain "tricking" you into feeling hungry.

My partner is a nursery worker and wrote this based on my ' too scientific for a five year old' description.

"Your brain is a puzzle. The weed copies matching pieces. When brain and weed pieces join together, it makes you hungery."

Your brain can naturally complete this puzzle when you need to eat however weed can complete it without your brain's permission.