So I've been exercising pretty regularly, heavily.
In the morning I either run for 40-60 minutes (run/walk appx. 3-4 miles) or I swim for 1/2 hour. Figure approximately 300-600 calories burned.

In the evenings 4 days a week I've been doing a cardio/plyometric work out program. (Shaun T's insanity, but while I'm doing the best I can, I'm not at Shaun T's intensity level). Shaun T says you can burn 1000 calories during this but I don't think that's true. I feel like I'm probably burning about 300-400 calories, but again, I'm not 100% sure.

The work out program suggests that my base calories are about 1700. I agree with this number. It suggests that in order to lose weight, I should be eating about 2600 calories.

Right now I'm losing weight. About 2-3 lbs per week. I'm eating approximately 1350-1500 calories a day.

What do you guys think? Should I stick to what I'm doing? Is this a non-issue? The guys I've been working out with scared me a little bit by saying that if my body isn’t getting the fuel it needs for these workouts it eventually enters “starvation mode” where it begins breaking down muscle and stores everything you eat as fat, which is obviously not what any of us want.

I'm exactly with you. Same type of working out and eating and I too am losing 2-3 weekly......felt pretty fatigued today so I've upped my protein intake. I am anxious to hear what others have to say.

I go by Daily Plate, it says for me 1400ish. They also say to eat back what you worked off so that you do not loose too much too fast, I never do though. If I eat 1400 then i have a 1000 calorie burn a day without exercise so I try to burn another 500, if I do that I should lose 3bs a week. I can never be certain about my burn so I am getting the BodyBugg this weekend and I will be able to test that to the T.

It's working, so stick to what you're doing.

Your calories sound fine to me, though you can stay closer to 1500 calories and still probably lose at a good rate. Don't worry about trying to calculate the number of calories you burn with exercise -- it's pretty much impossible and not at all necessary. I've never tried to figure out my exercise calories and managed to lose (and maintain) just fine.

Keep up the good work!

I really, deeply believe that it's damn near impossible to really count calories with any sort of fine precision, due to variable in food (water count and so on), instrument error, and user error. All these problems are compounded when trying to determine calories burned. I do think it's possible to be consistently inaccurate in one direction or another, and so your best strategy is just to stay with what works and if it quits working, try different things.

That said, if you are putting on muscle, you aren't burning it--are you putting on muscle? If you are, and are losing like that, I'd keep at it. If you haven't seen any new muscles after 4-5 weeks of that much exercise, I'd eat more, especially more protein. (I don't mean you should be bulked up, but you should be able to flex your leg and see/feel things moving around in a way they didn't before).

I'm losing inches. I'm pretty sure I'm getting muscle, but I'm doing mostly cardio- so the biggest muscle improvement is in my calfs/legs. The Insanity has some resistance training but not that much.

Thanks everyone, I think I'm okay, and I'll just keep an eye on things and if I'm feeling weak or not seeing muscle gain, I'll change things up a bit.