A group of overweight people.
A herd of extra large persons.
I was trying to get from one side of the mall quickly but I was slowed down by a large herd of fattle.
I was almost crushed by a stampede of fattle when the store opened it's doors on black Friday!
A group of obese people, or if a single person is astonishingly obese the word may be used to describe in the singular.
Look at those fattle being herded into the casino!