Calculate Protein Needs with the "Zone Method"

Using Lean Body Mass and Activity Level

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Some authors argue that the lean body mass (that is, the non-fat portion of the body) is the primary determinant of protein needs, and others argue that activity level should also be taken into account. Barry Sears ("The Zone Diet") and Michael and Mary Dan Eades ("Protein Power") are examples of authors who take both of these factors into account in their protein recommendations.

Lean Body Mass

Lean body mass is the amount of body weight that is not fat.

This includes bone, water, muscle, organs, and tissues. Lean body mass is considered important for metabolism as it burns more calories for energy than fat does.

Measuring your body fat percentage is the first step towards calculating your lean body mass. Simply, lean body mass is your total weight minus your body fat weight. There are several methods for calculating body fat. The easiest way is to use a body fat scale that uses bioelectric impedance. But you could also have it measured using calipers, a DEXA scan, or hydrostatic weighing.

If you weigh 150 pounds and your body fat percentage is 30 percent, that is 45 pounds of fat. Your lean body mass is 150 minus 45, which is 105 pounds.

Using Lean Body Mass for Protein Needs

According to the formula used by Sears, the pounds of lean body mass should be multiplied by the following, depending on activity level, to get the daily protein requirement in grams:

  • Sedentary: 0.5
  • Light activity (e.g. walking): 0.6
  • Moderate (30 minutes of moderate-to-vigorous activity three days per week): 0.7
  • Active (one hour of exercise per day, five days per week): 0.8
  • Very Active (10 hours of exercise per week): 0.9
  • Athlete: 1.0

Some experts also suggest that obese people go to the next highest category.

Because whatever activity they are doing is being done with extra weight, they are given extra credit for activity.

Example of Protein Needs Calculation

A person who weighs 160 pounds has 25 percent body fat. This person has 120 pounds of lean body mass. If the person is sedentary, he should consume 60 grams of protein per day, as 120 times 0.5 equals 60.

If the person is moderately active, 120 times 0.7 equals 84 grams, and so on. Note that a 180-pound person who has 30 percent body fat would also have 120 pounds of lean body mass, so the same figures would apply.

United States Institute of Medicine Protein Needs Estimates

It turns out that these numbers come pretty close to the standard way of figuring out minimum protein needs for most people. The United States Institute of Medicine uses a calculation of 0.37 grams of protein per pound of total body weight. This falls between the estimated average requirement of 0.33 grams per pound of body weight and the recommended daily allowance of 0.40 grams per pound of body weight. Athletes and heavy exercisers need more and may wish to double those amounts.

If you want to keep it simple without having to know your lean body weight, you might use those figures instead.

If you can calculate your lean body mass, see what the Sears/Eades method would recommend and compare it with the standard calculation.

Source:

Food and Nutrition Board, Institute of Medicine of the National Academies. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). The National Academies Press. 2005.

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