Bone mass is around 15% of your body mass, this can be c. 1% higher in obese people. Being obese can actually reduce bone density (through lack of exercise), whereas exercise can increase it.And Ethiopia.
As for the 'Big Bones' excuse. Ever seen a fat skeleton?
A new study published in the journal Metabolism found that obesity and type 2 diabetes led to weakened bones.
(eg: half a Big Mac contains the energy for 10 000 steps, and 1 M&M will get you up a flight of stairs)