Some of us were too small, not too big.
I was so skinny when I did my first Gnat trip that we could not get the seat straps to tighten on my shoulders. The Squiffer SNCO sent me back to the block to get my wooly pooly so that I had a wee bit more padding as he thought that on ejection I could slip out of the seat harness.
Last week I found it tricky trying to get the seatbelt on a PA28 to reach all the way round me. I was six and a half stone when I went to Valley and I am now 118 Kilos. I don't want to do the conversion to stones & pounds, I'd just get upset.