I am 45 - muscular build ( linebacker size ) 6ft - 275lb with soft midsection . I have decided to concentrate most of my time working out on cardio with about 25% spent on weights - my day job is slow and I don’t eat but 2 meals daily .
My question is without a major overhaul in my lifestyle , what minimum amount of protien do I need to consume daily in order to spare muscle loss from cardio and lack of food intake . I workout about 4-5 times week
6ft 275 is not linebacker size… It’s more like small defensive line size… 
It is actually not as much about the amount of protein as the timing and type of protein if preventing muscle loss is the goal.
IMHO the most important strategy to prevent muscle loss from the cardio portion of your question is to have a quick hit of a VERY rapidly absorbed protein before doing your cardio. The BEST product for this is MAG-10. The protein portion is composed of di and tri peptides that hit the bloodstream almost as soon as you take it in. And it has just enough carbs in it to prevent muscle wasting during cardio work.
So 1 serving of MAG-10, 20 minutes prior to your cardio sessions would be the no.1 strategy you should use to prevent muscle loss.
Now… that will mostly take care of preventing muscle loss from the cardio. But the fact is that if you consume a pretty high caloric deficit and are reducing the amount of lifting you will be doing versus what you normally do, you are very likely to lose some muscle mass., regardless of your protein intake.
Think about it. If you are in a restricted caloric state your body will eventually want to dump muscle. YES it will use fat for energy, but after a while if the caloric deficit is constant, the body will look for a way to decrease his caloric needs.
It’s just like money. If you get a pay cut you might be able to maintain the same lifestyle because of the money you put in the bank. But eventually you will have to start reducing your expenses.
Same thing with the body… and the tissue that drains the most energy is muscle. So the body will look to dump muscle to make it easier to survive the caloric deficit.
NOW, you can prevent muscle loss by convincing your body that it NEEDS to keep the muscle it has because survival would be more difficult without the muscle. If you engage in frequent, heavy lifting exercises the body will have a good reason to maintain its muscle mass.
But if you actually lift less often than you did prior to cutting calories, you actually tell the body that it’s okay to dump the muscle since you are not using them as much as you used to.
You might consume 400g of protein per day, it will not make a difference. The body uses protein where it’s needed. And if the body doesn’t have a reason to maintain, or increase its muscle mass then the protein will not be used on the muscles. It will either be used for other functions or will be turned into glucose to be used for energy.
That makes perfect sense ! I appreciate the advice ( especially from a TNation founder! ) I will lift hard and intense and make my body want to keep the muscle , or at least keep as much as I can . I will look for these di/tri peptide proteins as well . I love learning new strategies ! Thanks