How long does it take you to burn that 450 calories (Please tell me this isn't based on the notoriously inaccurate readings of a treadmill or elliptical)? How long does it take me to not eat those calories? (Hint: Not eating takes absolutely zero minutes:zero seconds) Also, how much more accurate is the calorie content of food vs the calculation of calorie expenditure of exercise (Assuming weight fluctuation and varying levels of intensity)? I lift heavily (for me) 3-4x/week but I don't count it toward my I/O because I don't lift heavily to burn calories, I lift heavily (with low reps/fewer sets) in order to preserve strength and muscle mass while cutting.
Fat loss is a war won in the kitchen, not in the gym. The only people who will tell you different are people who want to sell you something. Don't get me wrong, exercise is essential for overall fitness, strength, and physique - but it's about the hardest way to create a caloric deficit that you could find. Not only that, but if you exercise wrongly during a cut, you can actually damage your physique and strength goals if that's what you're going for. There is a time and place for more intense, calorie expending exercise during a cut (near the end) - but if you start at a high level of energy expenditure you have nowhere else to go when you hit the last few body fat percentage points or lbs/kgs - except to cut calories when your motivation and energy will be lowest. Unless you're chemically enhanced or have truly exceptional willpower, you will crash hard.
These programs (P90x, etc) will bring results for overfat noobs because pretty much any not-absolutely-stupid program can transform a couch potato into a moderately fit person. Nonetheless, they are overly difficult roads to that goal and their endless promotion is part of the reason more people don't have truly fit physiques or strength. I can't speak to endurance here because that does require a totally different approach. But if you want to exercise primarily to feel good, get stronger, and look good naked, there are much, much easier ways to get there and I only wish I'd have learned that lesson a whole lot earlier than I did.
Finally, if you rely on a coach or a workout buddy to get you fit, what do you do when that external crutch is gone? It's like hiring a chef to cook you meals to cut calories. Yes, you do require the motivation to follow through and you do have to suffer deprivation, but you never have to learn to do it yourself or find an intrinsically enjoyable reason to do it. In the case of these programs they are deliberately more difficult because convincing you that it's difficult creates the need for a coach in the first damn place.
