This is a question that can leave us puzzled if we look at these components as separate and unrelated. But the truth is that as you begin building muscle, your metabolic rate increases- thus making it easier to lose weight; especially if your caloric intake is less than your caloric output.
The standard caloric balance equation uses a formula of 3,500 calories equaling 1 pound. This means that in theory to lose 1 pound per week, you would need to create a deficit of approximately 500 calories each day below energy balance (the amount of calories it takes for you to remain at your current weight) either through food, exercise or a combination of both; 500 calories x 7 days/week = 3500 calories (DHHS, 2005). Curious to see how many calories are needed to maintain your current body weight? Feel free to check out the Daily Caloric Needs Estimate Calculator.
Effective fitness programs on the other hand should include 3 major components: Cardiovascular exercises to primarily burn calories and increase stamina, strength training activities that promote muscle building, and flexibility or stretching exercises to help prevent injury (ACE, 2013). Resistance is key to building muscle and enhancing bone strength. There was a recent study that challenged the notion that the only way to build muscle is through heavy lifting (high weight/low reps). Researchers found that muscle gains were not only equally possible with low weight and higher reps, but that it may be easier and perhaps more appropriate for some populations to work out in this manner provided that the exercises are done to fatigue (Burd, 2012). It was the fact that individuals are working an exercise to the point of fatigue that appeared more important for muscle gains than the actual amount of weight lifted.
Therefore, an effective “get in shape” plan may include a simultaneous effort of reaching a healthy weight through reduced caloric intake coupled with a comprehensive fitness routine to help minimize lean tissue (muscle) loss along the way.
U.S. Department of Health & Human Services (DHHS), AIM for a Healthy Weight, 2005; http://www.nhlbi.nih.gov/health/public/heart/obesity/aim_hwt.pdf
Burd, N.A., Bigger weights may not beget bigger muscles: Evidence from acute muscle protein synthetic responses after resistance exercise, Applied Physiology, Nutrition, and Metabolism, June 2012.