I don't know that there is any "rule" as everybody (and every body) is different. Personally, I've had good luck with the 40/30/30 carb/protein/fat mix that The Zone diet proscribes (though they want you to do it for EVERY meal, which sounds like an incredible PITA to me--I just go for that mix on an AVERAGE weekly basis--some days may be off but on average its pretty close).
This is just what works for me--YMMV, of course. You may need to tweak the mix to make sure you stay full at your calorie level and find out what gives you the best weight loss results.
Hope this helps!
47 M 5'8"
May 4, 2010...... 440? lbs. (Start FitDay Size 60 Jeans)
June 19, 2010.... 393 lbs. (First Weigh-in)
June 19, 2011.... 229 lbs. (164 lbs. gone in one year :-)
Current Weight... 185 lbs. (Size 36 Jeans)
Next Goal 169 lbs. (07/04/12)
Ultimate Goal 165 lbs. (12/31/12)
The best exercises for weight loss are Fork Putdowns and Table Pushaways.