Maintaing Muscle Mass

The usual story is that people lose muscle as they age due to disuse.  But more and more research I come across shows that nutrition may be even more important than exercise when it comes to maintaining muscle mass.  Here's a sampling:

• Alkaline diets (high in fruits and vegetables) favor maintenance of lean mass
• Higher protein intake helps maintain lean mass
• Insulin resistance leads to muscle wasting

So if you have all your nutritional ducks in a row, how much exercise and resistance training is needed to stave off muscle loss during aging?  I don't know the answer, but I think it's an interesting question - one that future research will hopefully be directed towards.