Nutrition 411: Calculating Your Patients` Caloric Needs

     Most people intuitively recognize the fact that in order to heal what ails us we must provide the body with good nutrition. In part, this means providing an adequate number of calories or energy each day to meet the body’s needs. Quite often, energy needs are elevated in patients with certain illnesses such as wounds. Determining the precise number of calories a patient requires can be challenging but in both acute and long-term care, a complete patient assessment includes estimating the daily number of required calories. The purpose for doing this is to set a daily goal. Once you have an idea of the number of calories a patient requires each day, the healthcare team can determine if the amount of food consumed meets the goal.

Components of Energy Expenditure

     While we commonly rely on several mathematical formulas to estimate caloric needs, it is important to understand that any formula is simply an estimate. In addition, rather than estimating caloric needs, formulas estimate caloric expenditure. This is a subtlety that escapes most practitioners.

     The total number of calories a person expends each day is based on three things: basal energy expenditure (BEE), physical activity, and the thermal effect of feeding (see Figure 1). BEE is the minimal amount of energy expended that is compatible with life. In other words, BEE is the number of calories an awake but at-rest person would burn to keep the heart, respiratory system, nerve impulses, and other unconscious metabolic processes functioning. Physical activity is voluntary movement; this component can vary the most between people. Sedentary people expend few while athletes burn many calories. The thermal effect of feeding is the amount of energy required to digest, absorb, transport, and store food. For example, the tabloids often report that celery is a miracle diet food because it contains a negative number of calories. They are alluding to the thermal effect of food and assuming it will take more calories to digest and metabolize the celery than the number of calories actually contained in the celery itself.

    Further complicating the issue of calories is the fact that total daily energy expenditure (TEE) is influenced by body composition and size, age, gender, hormonal status, fever, environmental climate, and other factors.

Methods of Calculation

     The simplest type of calculation used to estimate caloric needs is based on a standard number of calories per kilogram (kcals/kg) of body weight per day. The typical standards are 25 to 30 kcals/kg/day for normal, healthy individuals; 30 to 35 kcal/kg/day for patients with moderate illness, injury, or malnutrition; and 35 to 40 kcals/kg/day for patients with critical illness or injury. Consider a patient weighing 125 lb. The first step is to convert 125 pounds to kilograms by dividing the number of pounds by a conversion factor of 2.2. In this example, 125 pounds is the equivalent of 56.8 kg. For a patient with moderate illness, the daily estimate for calories ranges from 1,704 kcals (56.8 x 30) to 1,988 kcals (56.8 x 35). This is a range of almost 300 calories and provides only a general guide.

     The second way to estimate caloric needs is by using a mathematical formula. These formulas use information such as gender, weight, height, and age to predict BEE. BEE then is converted to TEE by adding factors for injury and activity. The total number of daily calories is derived using the following formula: Calorie requirements = BEE (activity factor + injury factor) +/- calories for desired loss or gain + fever factor. Table 1 lists four common energy prediction equations. Table 2 lists the injury, activity, and fever factors. Many studies have been done to evaluate the predictive ability of these formulas. A complete review of the evidence was conducted by the American Dietetic Association and can be found in their Evidence Analysis Library (www.adaevidencelibrary.com).

     It is important to note that the most precise measurements come from direct and indirect calorimetry. These techniques are generally reserved for metabolic units and research studies but a few companies recently developed relatively inexpensive handheld units. Although it provides superior data, calorimetry is not widely used. However, if you want to take your medical nutrition therapy care to the next level, it is a technology worthy of consideration.

Practice Points

     In practice, most clinicians use kcals/kg to quickly estimate caloric needs. Many registered dietitians use personal digital assistants (PDAs) or nutrition software to quickly and accurately perform calculations. These methods simply produce numbers to be recorded in the medical record as a starting point. The medical team must monitor meal intake, weight trends, healing, and biochemical data to obtain a full picture of nutritional well-being. Interventions should be implemented based on all pieces of data. So while we will continue to calculate and record our best estimate of caloric needs, you must remember to look at the whole patient and record the whole picture.

Next month in Nutrition 411: Vitamin C

Nancy Collins, PhD, RD, LD/N, FAPWCA, is founder and executive director of RD411.com and Wounds411.com. For the past 20 years, she has served as a consultant to healthcare institutions and as a medico-legal expert to law firms involved in healthcare litigation. Correspondence may be sent to Dr. Collins at NCtheRD@aol.com.

This article was not subject to the Ostomy Wound Management peer-review process.