Calculate Protein Needs Using the Zone Method

How Your Activity Level Alters Your Protein Needs

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Some health experts will argue that lean body mass (that is, the non-fat portion of the body) is the primary determinant of your protein needs. Others contend that your level of activity level should also factor into the equation.

The latter seems a fair argument given that someone with an active lifestyle would inherently burn more protein than someone who is relatively sedentary. Even if both have similar lean body masses, it doesn't necessarily make sense that both would have the same protein needs.

Calculating Lean Body Mass

Lean body mass is simply the amount of body weight that is not fat. It includes bone, water, muscle, organs, and tissues. It is considered an important measure for metabolism since muscle burns more calories for energy than fat.

Think of lean body mass as a simple mathematic equation: body weight minus body fat equals lean body mass (LBM).

To begin the calculation, start by figuring how what percentage of your body is fat. This is called, not surprisingly, the body fat percentage (BFP). There are several ways to do this:

  • You can use a body fat scale which employs something called bioelectric impedance to estimate your body fat. It is a simple technology in which high-frequency waves are sent through tissue to first determine to your total body water (TBW), the figure of which is then used to calculate your BFP. While the scales are readily available for home use, they are highly variable in their accuracy.
  • A simpler tool is called a skin caliper which looks rather like plastic scissors. To use a skin caliper, you would simple pinch an area of skin (such as under the upper arm or somewhere on the back) and clamp on the calipers. The thicker the pinched skin, the more fat there is. The tool is calibrated so that you can assess what your BFP is.
  • You can get a far more accurate reading with a technology known as a dual-energy X-ray absorptiometry (DEXA) scan. Clearly, the impediments to using this tool are convenience, cost, and radiation exposure.
  • Less invasive but almost as involving is a procedure known as hydrostatic weighing in which your body is placed underwater. In this method, the displacement of water is used to calculate your BFP. Of all the methods, this is considered the gold standard for measuring BFP.
  • The final method is called air displacement plethysmography in which air is used to make the displacement calculation rather than water. It involves costly technology that is not widely available.

Once you have calculated your BFP, you would simply multiply your body weight by the percentage figure. For example, if you weigh 150 pounds and your BFP is 30 percent, then 45 of those pounds would be fat.

Thereafter, to calculate your LBM, simply subtract your body fat (in pounds) from your body weight (in pounds). Using the same example, 150 pound minus 45 pounds equals 105 pounds. 105 pound is your LBM.

Calculating Daily Protein Needs

In recent years, a number of health pundits have established non-standardized measures by which to calculate your daily protein need based on both your LBM and level of physical activity.

One of these is Barry Sears, author of the bestselling book "The Zone Diet." While Sears' measures are not endorsed by any public health authority, many health and fitness professionals have embraced them as a means to create a more appropriate and individualized diet plan.

According to Sears, your LBM should be multiplied by the following activity level scales to determine your daily protein needs in grams:

  • Sedentary: multiply by 0.5
  • Light activity (such as walking or gardening): multiply by 0.6
  • Moderate (30 minutes of moderate-to-vigorous activity, three days per week): multiply by 0.7
  • Active (one hour of exercise, five days per week): multiply by 0.8
  • Very Active (10 hours of exercise per week): multiply by 0.9
  • Athlete: multiply by1.0

Based on Sears' formula, a 150-pound person with an LBM of 120 who is sedentary would need to consume 60 grams of protein per day. If the person were moderately active, the daily need would increase to 84 grams, while a performance athlete would need 120 daily grams and sometimes more.

Other Methods of Calculation

While Sears' formula is useful for designing a more tailored diet plan, it does have its shortcomings. For example, it does not take into account the impact that obesity may have on dietary protein needs.

As an alternative, the United States Institute of Medicine uses a more standardized scale of measurement, whereby your daily protein requirement would be calculated simply by multiplying 0.37 by your total body weight.

Using the above-listed example, you would multiply 150 by 0.37 to get your daily protein requirement of 55 grams. There is no variation based on activity level. It remains the same whether you are a couch potato or a decathlete.

Clearly, both formulas have their shortcomings and should only be considered a guideline for your daily protein needs. To attain a more insightful assessment, you should consider seeing a sports nutritionist who can perform in-office procedures to aid you in designing an appropriate diet plan.

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