Firstly I would like to point out that, the more consistent you are off-season, the easier it should be to make changes and see results pre-contest. For example if you eat six meals with the same amount of calories, protein, carbs and fat, day in day out off-season. Then come pre-contest you simply cut back your fat and carb intake, by decreasing the fat and carb content of each meal, keeping your protein fixed, start doing three cardio sessions a week, then watch how your how body responds, you will see and feel the difference in your physique. Therefore I recommend that you sort out your off-season preparation before you think about your pre-contest plan. Your off-season and pre-contest should work in conjunction with each other to ensure that you reach your full bodybuilding potential and keep on improving.
By now you should be realising that what works for one person may not work for another. Therefore the pre-contest diet plan that you should be using, should not be one used by "professional bodybuilder A" just because he always gets ripped, but one that is tailored to your metabolism, and meets your specific requirements. So lets get down to the "nitty gritty" of fat burning. This really doesn't have to be rocket science - we don't need to get into each possible cellular function, or anything else complicated. Simply put losing weight is all about calories.
For example if you require 2000 calories a day, to do everything that you do, go to work, do your exercise, etc etc, and you eat 2000 calories every day - then your body weight will remain constant. You will neither gain or lose weight. If you do however start consistently eating less than 2000 calories then you will lose bodyweight, and conversely if you consistently eat more than 2000 calories a day then you will gain weight. The rate at which you lose or gain weight will be determined by the amount of calories you cut back on or eat. So if you cut back on calories and start losing weight, how long will your body be able to lose weight for? I cannot give a definitive time bound answer to this. Your body will keep losing weight until it has reached a weight that can be maintained by your new calorific intake. Thus not only will you have lost weight, but you will also have decreased your body's daily calorific requirements.
To summarise so far - we now know how to lose weight. However we are not concerned with just losing weight - we specifically want to burn fat while holding on to precious muscle tissue. So how do we do this? As mentioned before the more consistent your off-season, the smoother your pre-contest should be. Thus off-season if you are eating enough protein to not only repair your muscles, but to allow then to grow, then you won't need to change the amount of protein you eat pre-contest. To temporarily go off topic, many bodybuilders tend to eat more protein pre-contest than they do off-season, thinking that it will help spare their muscle tissue when they drop their carbs low. If you look at the primary function of protein to a bodybuilder - it is used to repair and build muscle - not as fuel for your body like carbohydrates.
Therefore pre-contest when you are eating less calories than your body needs, it makes no sense to eat more protein than you do off-season. Firstly you will not be building any muscle tissue, secondly if you drop your carbs and increase your protein you are effectively eating the same amount of calories anyway. You are have already lowered your carbohydrate and fat intake, this combined with cardio will burn the fat away. So lets keep the protein fixed. As for your carbs, I suggest initially dropping them by around 15% depending on your metabolism. To really fine tune this, it is trial and error, always document what you are doing and assess your progress, not only using the weighing scales but the mirror, fat callipers and also photo's. This way you are getting an overall view of your progress. If you feel that you are losing too much weight too soon and you feel that your strength is getting sapped, then maybe you aren't eating enough carbs - in which case increase them. Again this is trial and error, to learn what works best for you and to fine tune things to your metabolism.
As for fat, we don't want to eliminate it all together, but I would recommend eating anywhere between 50 - 80grams daily regardless of your metabolism or weight. Good sources of fat would be a couple of egg yolks, Extra Virgin Olive oil/Safflower oil/Flax oil or Almond oil. NATURAL peanut butter, avocado pears and oily fish such as Salmon or Mackeral. Please remember that there are different types of fat, stay clear of butter, lard and other saturated and hydrogenated fats.
Flax oil (linseed oil) in particular has an excellent profile of omega 3 & 6 fatty acids. These types of fats will actually help metabolic process within the body that speed fat loss, instead of being stored as body fat. Since fat has 9 calories per gram, Flax oil can provide you with an excellent source of energy. Thus if you are smart about using these fats in your diet you can drop your carbs a little lower than usual and burn more body fat.
So there you have it folks.
Good luck - PJ.