Val Kilmer Weight Loss Secret ... Walk It Off!

Val Kilmer is half the man he used to be ... and we're told he shed the pounds the old fashioned way with determination ... and walking his ass off.

We're told 'Iceman' looked in the mirror and realized he had let himself go ... and decided to change everything.

There was no personal chef or magic diet pill ... just healthy eating and exercise, especially long walks on the beach by his home in Malibu ... which doesn't suck.

By the way ... walking on the beach is good exercise ... but not as good as playing volleyball with shirtless dudes.