The human body is an amazing piece of living machinery ever born. Basically speaking it is way ahead of your mind if you are one with both. Like changing your razor now and again will result in a better shave as you adapt and overcome. Our bodies will adapt to any load we put on it, as long as it's progressive.
To much too soon and your body will shout at you, 'Oi! That bloody hurts!'
Now if you look at some over weight people (lazy ones) you will see that their bodies have adapted to the gruelling hardcore workout of sitting, pint swigging, food stuffing and most likely finger pointing. This is a waste of a skeleton, a life. These people will do nothing, take a holiday because they have done nothing, then do nothing again, until they accumulate more waste, and then return to nothing. These people are self fish, they don't think they set examples for their children, and might not be there for them one day.
Now take the under weight people (lazy or trains to much and neglect food) I know that some people do honestly have health problem beyond their control and I really feel for these people. But this blog is for the other side of the park, trained or untrained. (I'm a strip of piss, but trained)
What ever you want your body to look like or achieve, just make it happen. Small steps, every thing in moderation, love yourself and enjoy what you do. In no time you will feel much better. Time will not wait for us so we have to blast now!