Pi / 20B09 / 17B02: Outline the daily nutritional requirements, including electrolytes, for a normal 70kg adult

20B09: Exam Report

Outline the daily nutritional requirements, including electrolytes, for a normal 70 kg adult

40% of candidates passed this question.

This topic is well covered in the recommended physiology textbooks. Many answers unfortunately simply listed the various components without providing sufficient detail; outline questions require some context around the key points as opposed to just a list.

Most candidates had a good estimate for the basal energy requirements of a resting adult. Good candidates were able to outline the g/kg daily protein requirements and the distribution of remaining energy intake between carbohydrates and lipids and included how this may change during periods of stress. They also stated the energy derived per gram of each of those food groups. Few candidates mentioned the need to include essential amino acids. Similarly, with fat intake, few candidates mentioned the need for essential fatty acids. A definition of “vitamin” would have received credit. Most candidates were able to classify vitamins as water soluble or fat soluble. Most candidates mentioned trace elements (with an abbreviated list) and mentioned bone minerals. A daily intake requirement for Na and K was expected, though not for bone minerals or trace elements.

17B02: Exam Report

Outline the daily nutritional requirements, including electrolytes, for a normal 70 kg adult.

21% of candidates passed this question.

The provision of nutrition is a core skill in ICU. An understanding of its key elements enables prescription and modification. However, most answers lacked detailed information which is available in the standard texts. Better responses outlined the caloric requirements including each major element (water, carbohydrate, fat and protein) along with the caloric values and
potential sources. Essential amino acids, fatty acids, fat and water-soluble vitamins were expected. A list of the requirements for major electrolytes and some of the trace elements were expected. Some candidates seemed to confuse calories, kilocalories and kilojoules.

Some answers did not provide the nutritional requirements, as asked, but instead discussed the fate of the nutrients; hence did not score marks. Candidates are reminded to read the question carefully.

Pi / 20B09 / 17B02: Outline the daily nutritional requirements, including electrolytes, for a normal 70kg adult

Definitions

Nutrient: a substance which is used by an organism to survive, grow, and reproduce.

Macronutrients: consumed in large amounts and are used for energy (to meet the energy expenditure) or are incorporated into the structure of tissues.
Micronutrients: consumed in small amounts and have various other physiological roles

Resting energy expenditure (REE): the amount of energy consumed (the metabolic rate) by normal physiological processes at rest.

Normal value (estimate) = ~1kcal/kg/h = 25kcal/kg/day
- For a 70kg adult = 1750kcal/day
Can be measured by indirect calorimetry, or estimated by formulas (e.g. Harris-Benedict)

Caloric Value of Food (CVF): the energy released from the complete oxidation of 1g of food – in kcal/g

kCal = unit of E used in metabolic studies of humans = the amount of E required to raise the temp of 1g H₂O from 15°C → 16°C
Calorie content of food = E released from food oxidation in the body

CARB = 4kcal/g

FAT = 9kcal/g

PROTEIN = 4kcal/g

Daily caloric requirements depend on activity, BMI, age
However, for sedentary 70kg adult approx. 2000 – 2500kcal/day
Daily caloric needs from each group: 2000kcal
- PROTEIN → 1g/kg/day = 70g x 4kacl = 280kcal
- FAT ~30% → 500kcal = 55g
- CARB ~45 – 65% → 1220kcal = 300g

Macronutrients

Protein

Requirement: 1.5-2g/kg/day in an ICU patient
- 6-0.68g/kg/day in healthy adults (more for males) – even more in the elderly

Dietary protein is digested to amino acids (AAs), which can be used to form proteins in the cells of the body.
- Non-essential AAs: these can be synthesized within the body (primarily in the liver) from intermediates (e.g. other AAs, sugars) – e.g. arginine, glutamine, tyrosine.
- Essential AAs: cannot be synthesized in the body from intermediates, must be included in nutritional intake – e.g. phenylalanine, methionine.

Protein/AAs can be metabolized for energy/ATP synthesis – this only occurs to significant degree in starvation or overfeeding, and therefore dietary protein is not typically used to make up the resting energy expenditure.
- CVF of protein: 4 kcal/g

Carbohydrates and Lipids

Glucose and triglycerides are oxidized to release energy, which is stored as ATP. The energy released is used to meet the REE. The recommended proportion of carbohydrates to lipids is 70:30.

Carbohydrates

Primarily converted to glucose -> oxidized for energy
CVF: 4 kcal/g of glucose
Requirement: ~70% of caloric goal
- 1750kcal x 0.7 = 1225kcal = 306g = approx. 4.5g/kg/day of glucose
- Minimum recommended amount is 2g/kg/day – to prevent neuronal hypoglycaemia

Lipids

Triglycerides -> metabolized to FFAs and glycerol
- FFAs oxidized for energy, glycerol metabolized in the glycolytic pathway
  - CVF: 9 kcal/g of fat
  - Requirement: ~30% of caloric goal
    - 1750kcal x 0.3 = 525kcal = 58g = ~1g/kg/day
Essential fatty acids (omega-3 and omega-6 FAs) – cannot be synthesized in the body and are important for cell structure and function. The 30% of caloric intake goal allows for adequate essential FA intake.

Water

Matches normal daily excretion of water
Requirement: 25-30mL/kg/day
CVF: 0 kcal/g

Micronutrients

Minerals

Inorganic substances (elements) needed in small quantities for normal tissue function.

Major minerals / electrolytes – requirement/day
- Na – 2mmol/kg (major extracellular cation)
- K – 1mmol/kg (major intracellular cation)
- Ca – 0.1mmol/kg (bone health)
- Mg – 0.1mmol/kg (catalyst for intracellular enzyme reaction)
- PO4 – 0.1mmol/kg (major anion of ICF. Co-enzyme)
- Cl – (major extracellular anion) no Australian recommendation, usually intake is the same as Na
Trace elements – elements present in the body in minute amounts, but without which a specific deficiency syndrome develops
- Fe – 10mg/day (more during menstruation and pregnancy)
- Zn – 15mg/day (integral to carbonic anhydrase)
- Cu – 2mg/day
- I – 150mcg/day (formation & function of thyroid hormone)
- Mn – 5mg/day
- Cr – 35mcg/day
- Se – 70mcg/day

Vitamins

Organic compounds needed in small quantities for tissue function – cannot be synthesized adequately in the body.

Fat soluble

Vitamin A – 900mcg/day (retinal eye pigment, epithelial tissue repair)
Vitamin D – 5mcg/day (increases with age – essential for bone formation ↑intestinal absorption of Ca²⁺ + PO₄^2-
Vitamin E – 10mg/day (fat oxidation, co-factor in ETC)
Vitamin K – 70mcg/day (clotting)

Water Soluble

B-group vitamins
- B1 (Thiamin) – 1.2mg/day
  - Essential for pyruvate dehydrogenase activity
  - ∴Deficiency ↓utilisation of carbs as nutrients
  - CNS + PNS depend almost entirely on glucose → degeneration myelin sheath, swelling of neuronal cells, neuritis, cardiac failure
- B2 (Riboflavin) – 1.2mg/day (oxidative phosphorelation)
- B3 (Niacin) – 16mg/day
- B6 (Pyridoxine) – 1.3mg/day
- B9 (Folate) – 400mcg/day (RBC maturation)
- B12 (Cyanocobalamin) – 2.4mcg/day
Vitamin C – 45mg/day (promotes hydroxylation -> essential for collagen)

Essential Amino Acids

9 of these:

i. Histidine

ii. Isoleucine

iii. Leucine

iv. Lysine

v. Methionine

vi. Phenylalanine

vii. Threonine

viii Tryptophan

ix. Valine

Included in the protein requirement (1g/kg/day)
Derived from animal & plant sources of protein

Essential FAs

Omega 3 FA
Omega 6 FA
Required for neuronal development
Not synthesised in body
Obtained from fish sources, nuts, green leafy veg
Approx 8g/day combined

Author: Joshua McLarty