Why Am I Losing Muscle & Not Body Fat?

During weight loss, your body gets some of its energy by breaking down fat and muscle tissue. The ideal goal while you're dieting is to encourage your body to preferentially utilize fat tissue and minimize muscle breakdown. If you find that you're losing mostly lean mass, it's a sign that you need to make some changes in your weight loss strategy to spare your muscles. Some of the most common reasons for excess muscle breakdown include losing weight too fast, cutting calories too low, not meeting protein needs, and not being active enough. Learn how to get back on the right track and preserve your hard-earned muscle.

If you find that you're losing mostly lean mass, it's a sign that you need to make some changes in your weight loss strategy to spare your muscles. (Image: imagenavi/imagenavi/Getty Images)

Cutting Calories Too Low

When you have weight to lose, it's natural to want it gone as fast as possible. In the eagerness to get the weight off, it's a common mistake to drastically reduce calorie intake to promote rapid weight loss. The problem is when you suddenly make extreme cuts in calories the body thinks it's starving, and since muscle requires more energy to maintain, the body begins to quickly break it down. In essence, dropping your calorie intake too low, too quickly puts you on the fast track to muscle loss.

An easy way to determine your minimum calorie requirements is to calculate 10 calories per pound of body weight for women and 11 for men. For example, if you're a female weighing 160 pounds, you need a minimum of 1,600 calories daily. If you're older or have less muscle mass, it may be a bit lower. Dropping your calorie intake below this number may accelerate muscle loss.

Failing to Boost Protein Intake

Believe it or not -- your protein needs actually increase when you cut back on calories. Therefore, it's crucial to bump up your protein intake to help preserve muscle during calorie restriction. While the conventional protein recommendation for maintenance is 0.8 grams per kilogram of weight, the British Journal of Nutrition published a finding in 2012, which reported that increasing to at least 1.2 grams per kilogram -- or 0.55 grams per pound of body weight -- helps preserve lean mass during weight loss.

A separate study found that men who ate the traditional 0.8 grams of protein per kilogram of body weight lost more muscle than participants who bumped up to 1.4 grams per kilo of weight. The results of that study are in the March 2013 issue of the journal Obesity.

Try boosting your protein intake to at least 0.55 grams per pound of body weight to reduce muscle loss. This means if you weigh 190 pounds, your target protein intake is about 105 grams per day as opposed to around 70 grams on a conventional protein intake diet.

Being Sedentary While Dieting

The old adage, "If you don't use it, you lose it," rings true when it comes to muscle mass during weight loss. When you engage in strength training during calorie restriction, it lets your body know that even though you've cut back on calories, your muscles are still needed and working hard. If you fail to work out while dropping pounds, it's as if your body says to itself, "This muscle requires more energy to maintain than fat does, and it's not being used, so I'll use some of it for fuel." Researchers concluded that inactivity during calorie restriction significantly increases muscle breakdown and impairs how well the body uses protein, according to a study published in the American Journal of Clinical Nutrition in 2007.

Additionally, a 10-week study involving overweight women reported that adding resistance training helped preserve lean mass during weight loss, according to results appearing in the 2010 issue of the Nutrition and Metabolism journal.

For weight loss, aim to engage in at least 250 minutes of moderate-intensity physical activity each week, including strength training two to three days a week.

A Healthy Approach to Losing Body Fat, Not Muscle

The number of total calories, rather than specific macronutrient ratios, determines weight loss. As long as you're restricting calories enough to lose weight -- but not so low that your body thinks it's starving -- and you boost your protein intake, it's not necessary to worry as much about the amount of carbohydrates or fat you're getting. Instead, aim to enjoy balanced meals and snacks built around whole foods. Make lean protein, whole grains, dairy, healthy fats, fresh vegetables and fruits the staples in your weight-loss diet. For guidance in planning your meals, consult a registered dietitian.