Yes, I must go on a diet! I really, really must!
Yes, it's true I'd loathe to try it, but if I don't, I'll bust!
I know it's hip, this losing weight, to join a gym and such,
But exercise, I'd simply hate, as I don't like it much...

My belly's not worth looking at, it bulges now and then...
I'd merely roll, flat on the mat and not get up again...
I'll make a stand and walk it off, at double time, I guess!
Who cares if others stare and scoff, if I weigh less and less?

I've never run a marathon and know I never will.
I'd simply say, I can't go on! No stamina or skill...
I'll walk the streets or buy a bike, until my belly's right...
I'll give up all the cakes I like, chew carrots day and night!

I'll switch to fruits and vegetables... I'll do the best I can,
I'll overcome all obstacles to look like Peter Pan!
Ta-ta to sweet treats, smokes and beers! I'll live temptation free!
Who knows? It may take months! Or years! Or decades! Goodness me!

Too late to talk me out of it! My mind's made up, my friend...
I'll get this weight off, bit by bit, on that you can depend!
I'll tone up muscles here and there... I'll fight the flab each day!
Before and after! Please compare... The diet's worked O.K.!

Denis Martindale

http://www.poemhunter.com/poem/i-must-go-on-a-diet/