Cardio will do a lot of good. Like Jasujo pointed out, walking is the best to start off with; not a stroll, but a good, slightly speedy walk. When you're ready, move up to a jog, with walk in between so you don't totally pass out.
Start drinking a ton of water. More than half the time if you think you're hungry, you're really just a bit dehydrated. I have an 18 oz bottle of water here at my desk at work that I feel up about 3 to 4 times a day. Not only will it clean out your system and hydrate you (Gatorade, Powerade, and those only hydrate, water will clean), but it will keep your energy level up as well since you will be shoving out toxins. Not a whole lot, but it'll keep things moving in your system.
If you want to diet as well as exercise, first watch how much you eat. Try eating only until you're not hungry, not until you're full and stuffed. It's easy and won't be too hard to maintain. Of course, there's the typical diets out there, low calorie, low carb, low sugar, blah blah blah.
If you can dedicate yourself to at least 30 minutes of some type of physical exercise a day, cardio or weights, it'll be a great stepping stone for you. I usually do 30 minutes of cardio, then another 30 minutes of various weights, crunches, stretching, things along those lines. If you want to put in the dollar investment, it won't hurt to join a health club and meeting with a physical trainer; they can help you design a work-out plan according to where you need the most work and what can best fit your lifestyle.
Yes, my mother is a health nut. Can you tell we share the same genes?
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