Brisk walking, rowing, running and cross training are the best exercises. For an overweight person I would recommend the cross-trainer as there is less impact and they will find it easier. Otherwise they'll complain it's too hard and give up.
I went from 230 lbs, which was definitely fat for me, to 185 lbs in about 5 weeks on a 500 calorie a day Protein diet combined with an hour a day of Lap swimming. It wasn't exactly the healthiest thing I've ever done, but I lost the weight. Overweight people also run, row, and cross-train.
.
Your body is pretty much like a car, with the heart as the engine. The more you rev it, the more fuel it burns. The form of exercise that burns the most calories is the one where youfind the best balance between intensity and duration.
For me swimming wouldn't be it. Either I'd go full tilt and burn out before using up any serious calories, or I go at my regular pace where I can't get my heart rate up enough to burn serious calories there either. But If I was a better swimmer that would probably change. My "best" exercises are cycling or skating, that's where I can get my heart rate up and keep it up long enough to make a real difference. In those I can maintain a steady heart rate of 150-160 BPM for hours, which will let me burn 900+ cals/hour. Keeping at it for 4-6 hours isn't a problem. Cross-country skiing, or skating with poles will bump my calorie consumption up some, maybe to 1200, but I can't really keep it up long enough to be significant.
500 cal/day diet really isn't advisable from any perspective. Don't try to follow that. You've probably spent years putting the weight on, so you should allow yourself some time to get it off. Also, the trick to a sustainable weight loss isn't through a diet, it's through a lifestyle change. And you need to spend some time on that to make it stick.
Swimming hard enough and being able to keep it up long enough to really matter in terms of calorie consumption is HARD. I'm not saying impossible, but I'd say that you'd need some prior training or previous experience of serious upper body workout to pull that off. Besides, for someone only eating 500 cals/day - well that person would have lost plenty of weight even if the only exercise was 5 minutes of thumb twirling daily.
The most effective way at burning calories is running and rowing followed by x-trainer.
The form of exercise that burns most calories is the one where you can strike the best balance between intensity and duration, and which exercise this is will be dependent on the person. For the "average guy" it is unlikely to be swimming and will most probably be an activity that has the legs heavily involved. My advice is to get yourself a heart rate monitor, one of those with a display that looks like a wrist watch. They're not particularly expensive, and most can do calorie counting these days. They're a really useful tool to help you evaluate and track your efforts. For someone starting out really unfit even running might be too intense, in which case walking at a brisk pace is a decent replacement. Remember, it's all down to getting the heart rate up and keeping it up for some time. Whatever gets you there will do the trick.
