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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;
Discuss the calculations for estimating calorie requirement?
Total energy requirement is calculated by adding
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?
Obesity-
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
The following can be useful to double check if concerns regarding over or underfeeding
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:
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-
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
Ref
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