As you can imagine, after writing a book about fasting for weight loss, I've had an amazing amount of questions pouring into my In-box, with the most common question being about fasting and losing muscle. Most people are still very concerned that they will lose muscle if they don't eat every 3 hours. My answer has always been, don't worry, from my experiences if you are resistance training then you won't lose muscle while dieting.

Then I received a very interesting question that went something like this - "If calorie restriction doesn't cause muscle loss, then what does?"

Great question. We all know that people who are bedridden and on a low calorie diet lose muscle. When I first starting writing Eat Stop Eat, and was running the idea past several dietitians for input, they all brought up stories of muscle loss in their patients who were bedridden and on a low calorie diet.

And since I am constantly saying that caloric restriction doesn't cause you to lose muscle if you are working out, then that leaves being 'bedridden' (or 'disuse' as they say in research) as the cause of muscle loss.

Ever break your arm and have to wear a cast, or know someone who did? Do you remember how skinny that arm was when the cast finally came off? Put a cast on your arm and your muscles shrink faster then an expensive new shirt in the dryer.

There was no change in nutrition, only a change in the amount the muscles were used, and the muscle wasted away.

In fact, 'casting' is so effective at causing muscle loss that it has been used in research to study something called 'disuse atrophy' or muscle loss from lack of use.

In a study conducted at the University of Nottingham, 22 male and female studies had casts put on their right leg for two weeks. Their diets didn't change, yet after only two weeks the cross sectional area of their quadriceps (the big muscles in your thigh) decreased by 10%.

No change in diet..but the muscle still decreases in size by 10%.

When you combine this information with other research that has shown that as long as you are working out and meeting some sort of caloric minimum, you won't lose muscle, you can come to the conclusion that if you don't use your muscles, then it really doesn't matter what you are eating, the muscle is going to shrink. However, if you are using your muscles, then as long as you are eating at least 80 grams of protein and over 800 Kcals a day (The amounts found in a recent research paper), you should not be losing muscle mass.

Now, If by some fluke accident you do break your arm, the research from Nottingham found that supplementing with Creatine Monohydrate can speed the rehab process, helping you build back your muscle and strength quicker than normal.

Resources:

Hespel P, et al. Oral creatine supplementation facilitates the rehabilitation of diuse atrophy and alters the expression of msucle myogenic factors in humans. Journal of Physiology 2001;526(2):625-633

Bryner RW. Effects of resistance training vs. aerobic training combined with an 800 calorie liquid diet on lean body mass and resting metabolic rate. Journal of the American College of Nutrition 1999;18(1):115-121