You need some carbohydrates to build or maintain muscle. Various studies, and our clinical results, however, have shown that the amount is much less than many have been led to believe. At 50 grams or more carbohydrates per day, most people are able to retain or build muscle. The exception is usually those who do a lot of high intensity cardio (for example running at 5 mph for an hour, 5 times a week).
One of the benefits of the moderate protein, relatively low carbohydrate (50-100g daily) eating plan used during the Weight Loss portion of the Lean for Life program is that people tend to retain more muscle than on either a very low carbohydrate or very low protein diets.
A body composition analysis test using bioimpedence can help determine if you are losing an inappropriate amount of weight from muscle.