Here's a story from my very-soon-wife-to-be's workplace. Some workmen moved a vending machine, but omitted to bolt it to the floor in its new location. The vending machine servicing man came to service the machine, opened the door and the machine fell on top of him. He lived to tell the tale. He was amply proportioned and it's quite possible that his fat layers helped protect his internal organs from terminal damage.

So, one good reason not to get lean. Here are some others:
1. At times of famine fat people have more chance of surviving, drawing on all those stored reserves.
2. Body fat is a good insulator, so keeps you warm in winter.
3. Body fat is less dense than other tissue and so it helps keep you bouyant in water.

Now, given the undeniable progress of global warming it's possible that we could be faced with food shortages, disruption of energy supplies and flooding. If that's the case then keeping a goodly layer of fat might be a wise move. Personally, I'm taking the view that well-stocked supermarkets and functioning central heating will continue to be a feature of my life for many years yet. And I live on a hill, so I'm not expecting to find water lapping around my feet any time soon.

Mind you, if a vending machine ever falls on me them I'm probably knackered.