I got knocked back for RauxAF at the medical the first time, I was joining flight ops so did not think about my weight (plus I had lied to myself for years). I lost 42lbs in 2 months, and I went on to lose (and keep off) 80lbs in about 6.
First was cardio and I joined a gym, and I will tell you this: I got on a treadmill, did 900m at 9km/h and almost died, that was the shape I was in. So I sacked that and went to the bike, I peddled for weeks, steadily building up a pace and distance until I was ready to go back on the treadmill. I then started at 15min run going 10km/h and over the course of 2 weeks built that to 25min (a guide I went by said if you can get over the 20min mark then you can run for ever). Dropped the time back down, increased the speed, built back up to 25 min. Rinse and repeat. Eventually had a routine of half an hour on a treadmill twice a week at about 11km/h and once a week I did a mile and a half to the old pre-joining standard (12:30 for my age), I can now do that run in 10 min and use that as my confidence test before RAFFT.
Diet. Parallel to that I started on an horrific diet routine. Working on the understanding that a healthy male (with AVERAGE weight) needs 2500 calories a day will get you into all kinds of trouble. First thing is to google weight calorie sites, a friend who is a PE teacher told me about this. Basically the heavier you are the more calories a day you need to consume to simply maintain that weight. The other contributors are right about the number of calories required to lose a pound but simply eating 2500 a day will result in weight loss for the overweight. You have to think about the difference between your consumption and the actual number needed to maintain your current weight, that is where the loss is made. Although you also have to look at calories burned over a week rather than a day because your body does not work that fast!
So being a computer geek to trade I put all those numbers into a spreadsheet. I put low average calories burned for my workouts and overestimated my intake. I then started to measure myself and I had a sheet that told me how many calories I had to burn to maintain that weight. That was my motivation. I watched the numbers tick down and when I hit my BMI of 32 I called in for my next medical. I was another 4kg lighter when I attended my appointment.
I was lucky that I had an M&S beside my office, they sold a very nice low cal range. Their tuna salad was very low cal and quite filling! Weight watchers meals as well. I did one week 2500 a day and one week of 1000 a day.
It was tough, and I could not stand up to quickly because I tended to then get light headed and fall over!
However that may not be for everyone!
It was my birthday last week and I ate too much, but I am back on a week of diet to even things out, I know I can do this now so you can have the odd splurge when you get in!
Good luck.
DT_Xtremez_39: