In order for belly nuts to occur, two conditions must be met.
1. When a fatty's enormous stomach becomes large and saggy enough that it must be tucked into the pants.
2. When said fatty chooses to wear pants that are a) too tight to contain said belly, and b) have a seam that devides said belly into 2 distinct parts, taking the form of a pair of giant balls.
It should also be noted that belly nuts shows no gender discriminaation, and may occur on males and females, provided they are a lardie.