Diet and exercise, everything else is just a fad...
The fitness program reg is AFI 10-248 (I think), you can download it at the Air Force reg page. I can't access it now due to my hack-filled Belgian ISP, but I was just looking at it today as we were having a similar discussion at work.
There are two "failures," and depending on how bad you fail you will be enrolled in two separate programs. I used to administer the weight management program while a commander, and as long as you made progress within the standards (I think it was a pound a week, something like that but don't quote me as I always check the regs when administering them), you were fine. However, it only takes a few failures to make progress to initiate discharge.
In my experience the biggest problem with folks, other than those who just didn't care, was they tried a fad diet or some other extreme. It doesn't work, sorry. Adkins and all those have drawbacks, and if you don't exercise you won't make the required progress. The Health and Wellness Center (HAWC) provided all the guidance a person needed, if you can contact them I highly recommend it.
I hate to tack this on but I never had anyone survive the weight management program once they started to not make progress standards. Maybe the ding was too much for them, but once they got their first one each and every one of them ended up going out the gate. Unfortunately that included a lot of good people who otherwise had good careers, but the fitness program is no different than any other requirements in the USAF...either you meet them or you get out. That may be brutal but it is a fact of life...
Good luck, a positive attitude is the first and foremost requirement for beating this!
Cheers! M2