In the mid 80's, long before I began my career in EMS, I worked in radio as a DJ. Like an EMS service that posts trucks throughout their service area in parking lots (like mine), leaving us sitting in trucks for hours doing nothing in between calls but snacking & napping, DJ's do pretty much the same thing. I did a 1900-0000 show five nights a week, plus one weekend shift. With nothing to do but play music, speak into the mic every 8 minutes or so, drink Cokes & order pizza, I gained 20 lbs in 4 months. I was only 20 years old & never weighed more than 120 lbs before then. If you're more successful in radio (which I wasn't), or work in a larger market (which I didn't), say, on the wacky morning show, you get free food sent to the studio from restaurants wanting an on-air mentions, junk food at personal apperances & concerts, etc. Those scenes in "Private Parts" of Howard Stern wolfing down buckets of fried chicken were pretty true to life.
So, while "air personalities" (that's what they call themselves now) aren't the most physical people in the world, those who take the time to eat right and exercise (like Stern) look great well into middle age. Those who don't look like Bubba the Love Sponge.
The real reason you hear about so many radio people on diets these days is because they're getting free gym memberships & personal training in exchange for commercial air time. Wish I'd had that in the mid 80's.