Estimating calorie requirements

Discuss the principle of estimating calorie requirement?

Estimating calorie requirement is an essential component of nutrition support to avoid under or over feeding. Energy requirements can be calculated;

  • Using doubly labelled water technique or indirect calorimetry. However these methods are not practical in the day to day clinical practice.
  • Arbitrary estimates of energy requirements per kilogram body weight. This is an imprecise method. Adult energy requirements tend to be between 25-35Kcal/kg (NICE 2006)
  • Using predictive equations like Schofield or Harris Benedict equations

Discuss the calculations for estimating calorie requirement?

Total energy requirement is calculated by adding

  • Basal metabolic rate (BMR) or REE (resting energy expenditure) using predictive equations
  • Dietary induced thermogenesis (DIT) – energy used during digestion and absorption (usually 10%). However considerations are different when using artificial nutrition. Continuous NG feeding appear to have little effect on energy expenditure; however those receiving bolus feeding DIT may account for 5% of the total energy expenditure and this figure should be added to the estimates of the energy needs.
  • Activity level- Clinically, the following factors combining activity level plus DIT can be used
    • Bed bound immobile                               BMR + 10%
    • Sitting/bed bound immobile                    BMR +15-20%
    • Mobile around ward                                BMR +25%
  • Stress level- use with caution due to the risk of overfeeding. The period during which stress factor is applied depends on clinical judgement Elia’s nomogram can be used to guide stress level adjustments Sepsis/abscess-20%, surgery- uncomplicated- 5-20%, complicated surgery- 25-40%, ICU- ventilated- 0-10%, ICU-sepsis-20-60%, COPD- 15-20%, CVA- 5%, Cerebral he-30%, Acute Pancreatitis-10% (Todorovic and Micklewright 2004)

Schofield equation is commonly used to calculate energy requirements in UK.

Schofield equation (based on DoH 1991)

Age (years) Male Female
10-17 BMR=17.7XWt (kg) +657 BMR=13.4 XWt (kg) +692
18-29 BMR=15.1 XWt(kg) +692 BMR=14.8 XWt (kg) +487
30-59 BMR=11.5 XWt(kg) +873 BMR=08.3 XWt (kg) +846
60-74 BMR=11.9 XWt(kg) +700 BMR=09.2 XWt (kg) +687
75+ BMR=08.4 XWt(kg) +821 BMR=09.8 XWt(kg) +624

Total Energy requirements- BMR +activity level (+DIT) +stress levels
Harris-Benedict Equation (BEE):
Females: 655.1 + [(9.56 x W) + (1.85 x H) - (4.68 x A)]
Males:      66.47+ [(13.75 x W) + (5 x H) - (6.76 x A)]
W = weight in kg; H = height in cm; A = age in years
NB- Pregnant women in second or third trimester: Add an additional 300 kcal/day

Discuss calculating energy requirements is specific clinical conditions?

In obese pts (BMI>30kg/m2), predictive equations tend to overestimate energy requirements. Ideally energy requirements should be assessed using indirect calorimetry (ASPEN 2002), however this is not feasible in clinical practice.
Feeding to actual body weight (ABW) sustains obesity and may precipitate metabolic effects of overfeeding such as hyperglycemia and respiratory distress (NICE 2006). Conversely feeding to an ideal body weight (IBW) will promote weight loss but may compromise glucose tolerance and wound healing. A balance is thus needed.

Todorovic and Micklewright 2004 suggest the following

  • For non stressed pts- calculate requirements using Schonfield equations and then subtract 400-1000Kcal/day to encourage a decrease in energy stores
  • Mild-Mod stress- use BMR calculated using ABW. In order to prevent adverse effects of overfeeding, do not add the activity or stress factor
  • Severely stressed- calculate BMR using ABW and add a stress factor
  • Monitoring is essential and should include nutritional parameters, blood glucose and RQ (should be 0.8-0.9)

The following can be useful to double check if concerns regarding over or underfeeding

  • Use 19-21 Kcal/kg actual body weight
  • BMR using Schonfield equation and adjusted body weight (ABW+IBW/2), then add activity and stress factor as usual
  • Ireton-Jones energy equation for obesity

Liver disease
Calculations should use dry body weight and adjustments made for fluid overload and ascites

Discuss the nutritional needs of an individual?

NICE 2006 guidance suggest that nutrition support prescriptions should consider individual needs for energy, protein/nitrogen, fluid, electrolytes (Na/K), minerals (Mg, Po4), other micronutrients (vitamins and trace elements) and fibre
For example, NICE 2006 suggest
For people who are not severely ill or injured, nor at risk of refeeding syndrome, the suggested nutritional prescription for total intake should provide all of the following:

  • 25–35 kcal/kg/day total energy (including that derived from protein)
  • 0.8–1.5 g protein (0.13–0.24 g nitrogen)/kg/day
  • 30–35 ml fluid/kg (with allowance for extra losses from drains and fistulae, for example, and extra input from other sources – for example, intravenous drugs). In general fluid input should be 500-750 mls more than the output.
  • Adequate electrolytes, minerals, micronutrients (allowing for any pre-existing deficits, excessive losses or increased demands) and fibre if appropriate.

Protein/ nitrogen requirements

Protein is the only macronutrient that contains nitrogen. Approximately 16% of protein is nitrogen, so 1 gm of nitrogen is equivalent to 6.25 gm of protein. In practice nitrogen is often calculated when estimating requirements for parenteral nutrition while protein is used at all other times. Nitrogen support should aim to keep the body in nitrogen balance i.e. N2 intake is equal to N2 loss (in urine, stool, fistula output etc). N2 balance may not always be achievable (in such cases aim to minimise N2 losses)

Protein needs-

  • Maintenance- 0.75gm/kg/day (DoH 1991) – This overestimates protein needs in obese- so 75% of the estimated protein requirements should be use if BMI is > 30 and 655 if BMI>40
  • Stress
    • Mild stress level: 1-1.2 g/kg/day
    • Moderate stress level: 1.2-1.5 g/kg/day
    • Severe stress level: 1.5-2 g/kg/day

    A more precise estimate of the N2 needs can be obtained by measuring 24 hr urinary urea. gm protein lost/24hr= mmoles urinary urea excreted in 24 hrs/5 (not reliable in liver or renal failure)

Carbohydrate (dextrose):   5 g/kg/day
Fat- 20-40% of the calorie requirements


  1. Manual of Dietetic Practice.  By Briony Thomas, Jacki Bishop, British Dietetic Association. Blackwell Publishing, 2007 ISBN 1405135255, 9781405135252

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