We all know now that when we train, we are merely providing the stimulus for our bodies to become bigger and stronger (to over-compensate) as the act of high intensity weight training actually breaks down muscle tissue. We also know that we don't actually get bigger when we are in the gym training. The recovery process is slow, and can take up to a week for a certain body part to fully over-compensate.
Protein is the raw material for muscle growth - the building blocks if you may. Now when you take protein out of the equation, it is like asking the builders to finish building the house by the deadline, yet you have taken away the bricks.
Remember, whilst protein is a vital nutrient, so are the other macronutrients. Keep your diet balanced, and stay within your body's optimal protein requirements.
The amount of protein that an individual needs has been the topic of much controversy over the years. I can tell you this for certain though. The general RDI of protein is inadequate for a hard training athlete. In Australia, I have seen the RDI of protein range from 0.8 to 1.2 g per kg of bodyweight or up to 1.5g per kg of bodyweight. Following these recommendations in conjunction with a high intensity weight training program, you would be lucky to hold onto the muscle mass of an 8 year old girl, let alone make any noticeable increases in lean body mass. I have seen other recommendations of up to 3g per kg for strength athletes, but I still feel this might be inadequate. I have experimented myself with various amounts of protein and found that when I consume near 5g per kg of bodyweight is when I make noticeable gains in size and strength. When I am consuming high amounts of protein, I find that I recover quicker and suffer less aches and pains. Coincidence, I don't know. All I know is that when I reduce my protein consumption, the gains will slow.
The best recommendation I could give on protein consumption is to increase it to a level where you feel you are getting the best results. This for you might be 3g per kg or even higher, the trick is finding what works for you. I can tell you this for certain though - chances are right now, your not eating enough!
If you need definite answers here, I recommend that you find a good sports nutritionist that you can work with face to face for an optimal eating plan tailor made to suit you.
Protein requirements during a dieting phase
This is where the line can become somewhat blurred. When it comes to building mass, protein is the number 1 macronutrient you should be concerned with, but to lose fat, it all comes down to energy requirements (calories). When you are trying to 'cut up', your focus needs to be on total calories. To burn fat, you need to be in a calorie reduced state, and you can to this only 2 ways. You can eat less energy (food) then your body needs to perform all its required functions, or you use more energy then you take in by completing regular weight and cardio-vascular training sessions. The best results are achieved with a combination of the 2.
Now how do you juggle keeping a high protein level when dieting down to single digits? At this stage, your goal of ultimate fat loss will be more important then keeping super high protein levels, but you still can get the best of both worlds. As your diet progresses and you are steadily losing body fat (BF), the time will come when you need to reduce calories to keep the process going. Now small changes work best, so to drop 200 daily calories isn't really that big of a deal at the start. Take out 50g of crabs or 22g of fat (both equate to 200cals). For the first few weeks you can just skim away from the excess crabs and fats, but the time will come when you need to reduce protein figures to keep dropping cals. Start from reducing protein figures from meals away from your training times. I.e.: if you train in the morning, skim 10g each off the last 5 meals of the day. This will bring on another 200cal reduction, whilst still capitalizing on recovery.
If you get to the stage where you have dropped everything from everywhere from your diet except from your training recovery meals, then you simply cannot drop anymore calories, and nor should you try. If you are absolutely determined to get even lower BF numbers (believe me, if you have gotten to this stage then you are VERY LEAN), you can increase cardio intensity and duration. Remember though, don't overdo it. The more you do, the more your body will require protein for compensation. Drop too far or train excessively, then you can do more harm then good.
Protein consumption on training days vs non-training days
Reducing protein consumption on non-training days per your normal training day requirements is asking for minimal results. Irrespective of what day it is and your workload, your protein requirements need to remain optimal. If you are in the off-season, I would always recommend eating more protein whenever you have any doubt. If you are a hard training athlete, the only side effect that you might experience is added lean body mass, and isn't that the reason we all train in the first place?