Hi James
I think there could be something in what the Doctor says If the extra weight is on your stomach it affects the posture and puts a strain on the spine.As you know with our posture being as lovely as it is it dosent take much to cause spasams and pain.
I know if I carry a light bag for a short distance it causes pain in my middle spine. Also because of our wonderfull posture our centre of gravity is a few feet ahead of us laugh2 so it dosent take much to affect us.

Kevin