Okay here's my
Get a bicycle, and ride it. No, that's not all. Start with 20 minutes, a day or every other, of just riding around for about a week. Eat bananas as a supplemental source of snack food. Second week, add on another 20 minutes a ride for a total of 40 minutes total ride time. Keep it at 40 minutes for a couple weeks adding on 20 here and there. This all depends on how much you like to ride, of course. I've never been a runner, and joint stress is minimal on a bicycle. Your crotch will feel a little achy for about a week, until the fatty tissue and muscle accomodate the load. It also depends on the saddle, but any bike will do.
As far as nutrition, I am stressing that a lot of what has been shared is good information, BUT, do not try and ask your body to accomodate a major nutritional adjustment early on. Just concentrate on riding regularly. Some folks say 4 days, some say 5, I actually ride a minimum of 20 to 30 miles daily ( a minumum of 6 days a week ). Then again, I stress, I've built up the endurance over the past five years. I checked with my doctor, and he said for the benefits of my cardio / cholesterol / emotional (general well being) that riding everyday isn't bad for you. If you feel tired on a day, take the day off. Just don't quit indefinitely.
You have to ask yourself, do yo wanna get fit, or just lose a few pounds ?. I got fit, and lost a lot of weight just by riding a few miles daily. Then I started upping the ante here and there. Adjusted my nutritional intake (no red meat, fish and poultry, fruits and veggies, less soda, more water etc....). It was easier than I originally thought it could be. Currently I'm 42, 6'2", 200 lbs (all the time), chest 42", waist 34". I eat and drink as much as I like, although my portions have dropped a bit, and I eat what agrees with me. I haven't touched a fastfood burger in eight years. I also cut out fried foods. Too much grease for the body to process.
The older we get, the more important it is to take care of the ol' body. I'm not talking Jack Lalaine here, but a little goes a long way.
"IMPORTANT"......The one thing I'll warn you about, as it has been offered. DO NOT start ingesting huge amounts of WATER.
"DO NOT".
Your body currently isn't ready to process that much water, it'll deplete your salt and beat up your kidneys. I do recommend, you start drinking "more" as needed. I drink distilled "all" the time. It's the purest hydration known to man, and on a cellular level it's exactly the same as what your body filters and feeds the cells. I also recommend nutritional supplements but start with a decent multi-vitamin.
I won't tell you how to do it. Everybody has a formula. Make up your own as you go. What works for me, doesn't work for everybody, just me. From where I started I've come a long way, and I feel awesome for an old man of 42..... Sounds stupid, but really, try the bike. Let your body lead for a change.