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I've just been curious about this...I'm not planning on doing this or anything!
So say you lift weights but don't eat/eat very little and you eat no (or little) protein. Would the weight lifting be pretty much pointless, or would you lose muscle at a slower rate than if you didn't lift weights (even without protein to repair the muscles)?
The process of weightlifting to build muscle is by lifting weights you are actually breaking down muscle which the body repairs over the course of 2 days and actually builds more muscle in the process.
If you don't eat much and no or little protein, 2 things happen.
1. The body actually consumes muscle to survive.
2. The body has no nutrients or raw materials to repair the broken down muscles, therefore resulting in a net loss to those muscles that were affected by the lifting.
Think of prisoners of war used for construction work for the enemy. They were fed very little food and generally what they were fed was poor quality. The result was they became emaciated and their immune systems were compromised. Most did not survive if this went on for much time.
This is a very general answer, but I think it gives you the general idea.
Consuming little protein while dieting/fasting AND doing resistance exercise would be difficult- one would probably feel pretty weak, however, there have been some studies that suggest that strength training while on a very low calorie diet may preserve muscle strength and lean body weight. I don't know if this helps answer your question at all. Here's one such: http://www.jacn.org/content/18/2/115.full
Thing is, I don't know what the protein content of these diets were...