The Effects of Aging on Body Composition

In the past few articles, I’ve illustrated the plethora of reasons why the scale is not an accurate assessment of your level of fitness and then discussed the two most popular methods of determining body composition: Caliper Measurements and Bioelectrical Impedance. You will recall that measuring body composition is superior to stepping on the scale. Body composition refers to the body’s relative amounts of fat vs. lean body mass (organs, bones, muscles). Optimal body composition is best gained through proper diet and exercise. (We’ll discuss how to improve your body composition next month.) Examples of poor body composition are underdeveloped musculature or excessive body fat. Being overweight (that is, overly fat) is the more common problem.

Let’s begin with the underlying cause of weight (fat) gain for most men and women, including those who eat reasonably and exercise regularly. First, unless you strength train with intensity, you lose about 5 to 7 pounds of muscle tissue every decade of adult life. Aerobic activities, as good as they are for cardiovascular fitness, do little to prevent the loss of muscle during the aging process.

Second, the 5-7 pound per decade muscle loss leads to a 3-5 percent per decade reduction in resting metabolic rate. Because your resting metabolism accounts for about 70 percent of your daily calorie utilization, this seemingly small change in energy expenditure is largely responsible for an average fat gain of 15 to 20 pounds per decade. Keep in mind that a 20-pound per decade fat gain represents only 19 unused calories per day. Ouch!

Third, low-calorie diets and general exercise programs are effective for temporary weight loss (the loss of both fat AND muscle – this is NOT good) because of a negative energy balance (fewer calories eaten than needed for maintenance). However, neither approach addresses the underlying problems of fat gain, namely, less muscle and lower metabolic rate. In fact, low-calorie diet plans result in further muscle loss and metabolic slowdown, thereby making future weight regain almost inevitable.

Fourth, the only activity that reverses the age-related processes of muscle loss and metabolic slowdown is strength training. Based on our research, 10 weeks of basic resistance exercise builds, or replaces, 3 pounds of muscle, which increases resting metabolic rate by about 7 percent, and results in 3 pounds to 12 pounds of fat loss. Obviously, this is an excellent means for attaining and maintaining a healthy body composition and body weight.

For example, a typical low-calorie diet plan may result in a 9-pound fat loss and 3-pound muscle loss. On the scale, this appears as a 12-pound weight loss, but it really represents 9 pounds in the right direction (fat loss) and 3 pounds in the wrong direction (muscle loss), for an actual body composition improvement of 6 pounds (half what the scale indicates).

Conversely, a typical strength-training program may result in a 9-pound fat loss and a 3-pound muscle gain. On the scale this appears as a 6-pound weight loss, but it really represents 9 pounds in the right direction (fat loss) plus 3 pounds in the right direction (muscle gain), for an actual body composition improvement of 12 pounds (twice what the scale indicates).

In measuring body composition, it’s not only important what the result is, but also how you arrived at it. For example, let’s say you’re a woman with a skinfold or bioelectric impedance body fat measurement of 22%. At first glance it seems that you fall into a healthy body fat range. The problem is, since the error factor for both of these methods is up to +/-8%, this number could mean your actual body fat could be as low as 14% (risky – low body fat) or as high as 30% (borderline excess fat). Inaccurate information like this is no better than no information at all, and can be downright dangerous if being used to determine an appropriate diet and/or training program. This is why it’s so important to receive an accurate body composition assessment. It’s the only way to get the proper information necessary for making sensible decisions regarding nutrition and fitness programs.