As you fill out the rows in your progress chart each week, keep an eye on your lean body mass (LBM), especially the trend over time.
Don't panic if you see an initial drop in LBM. Nearly everyone on a calorie and/or carbohydrate restricted nutrition program will see substantial water weight losses, especially in the beginning. Because water weight losses are reflected in LBM (muscle is mostly water), this will show up in your LBM number. You cannot measure water weight, muscle weight and fat weight separately with a standard body composition test (skinfold, etc). When your first start your program, chalk up this initial LBM drop to water weight and don't be overly concerned.
Water balance can affect your weight in the opposite direction too. Your muscles are like sponges for carbohydrates and water. If you eat more carbohydrates one day than usual, and also increase your fluid and or sodium intake, it's not uncommon to see an increase in bodyweight of three to five pounds - especially if you're on low carbs. Are those three to five pounds overnight solid muscle? Of course not. But if your official weekly weigh-in falls on that day and your body composition is the same or lower, you will show a several pound muscle gain. This simply reflects glycogen and water in the muscles. In bodybuilding lingo, you "filled out."
This is why you must be consistent with your weigh-ins and why you shouldn't panic if you see a small drop in LBM. If your LBM continues to drop week after week in any significant amount, then there may be cause for concern. A continual downward trend over time in your LBM number clearly shows that you're losing muscle tissue. Continuing with this pattern will cause your metabolism to slow down and this will eventually decrease your rate of fat loss.
Look closely at your ratio of fat lost to lean mass lost. If you lose more lean mass than fat, that's a clear sign that some of the weight was muscle. For example, suppose you lose 3 pounds in one week with 1.2 pounds from fat and 1.8 pounds from lean mass; don't pat yourself on the back for losing weight - you lost more LBM than fat. You should also look at the total amount of weight you lose each week. Your optimal goal for fat loss is to lose only one or two pounds per week. If you lose more than two pounds of weight per week, you're probably losing muscle.
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