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Nutrient Requirements and Dietary Assessment

Chapter 343 | Harrison's 22e · Part 10 – Gastrointestinal Disorders · Chapter 343

Key Clinical Points

  1. Nutrients are essential substances not synthesized in sufficient amounts by the body; deficiency leads to growth impairment, organ/metabolic dysfunction, and failure to maintain nitrogen balance.
  2. Conditionally essential nutrients (e.g., arginine, glutamine) are required only under specific conditions like infection, trauma, or during development.
  3. Protein RDA is ~0.8 g/kg of desirable body mass; animal proteins have the highest biological value.
  4. Fat should be ≤ 30% of calories, with saturated/trans-fat and polyunsaturated fats each limited to <10%.
  5. Carbohydrates should provide 45–55% of total calories, with added sugars ideally <6%.
  6. Water requirements are 1–1.5 mL per kilocalorie of energy expenditure.
  7. Estimated Energy Requirement (EER) is calculated as REE imes PAL; use 1.2 to 1.4 for sedentary individuals to avoid overestimation.
  8. The brain requires ~100 g of glucose/day, while other tissues require ~50 g/d.
  9. Alcohol provides 7 kcal/g but is not considered a nutrient.
  10. Protein tolerance is significantly decreased in patients with renal insufficiency (uremia) or liver failure (encephalopathy).

DEFINITION & CLASSIFICATION

• Nutrient Definition: ◦ Definition: Nutrients are substances that are essential but not synthesized in sufficient amounts in the body and therefore must be supplied by diet. ◦ Consequences of Deficiency: ◦ Growth impairment ◦ Organ and metabolic dysfunction ◦ Failure to maintain nitrogen balance or adequate status of protein and other nutrients • Nutrient Categories: ◦ Energy-providing: protein, fat, carbohydrate ◦ Organic Nutrients: 9 essential amino acids, fatty acids, glucose, 4 fat-soluble vitamins, 10 water-soluble vitamins, dietary fiber, and choline ◦ Inorganic Nutrients: 4 minerals, 7 trace minerals, 3 electrolytes, and ultra-trace elements (must be supplied by diet) • Conditionally Essential Nutrients: ◦ Definition: Not required in the general diet but must be supplied to specific individuals ◦ Target Populations: Individuals with genetic defects; those with infection, disease, or trauma; developmentally immature infants ◦ Examples: inositol, taurine, arginine, and glutamine • Amino Acids: ◦ Essential (9): histidine, isoleucine, leucine, lysine, methionine/cystine, phenylalanine/tyzyine, threonine, tryptophan, and valine ◦ Non-essential: alanine, arginine, aspartic acid, glutamic acid, glutamine, and glycine (can be converted to glucose for energy and gluconeogenesis) ◦ Clinical Note: When energy intake is inadequate, protein must be increased because amino acids are diverted into pathways of glucose synthesis and oxidation.

Inorganic Nutrients (Table 343-3)

• Mineral Requirements: Table 343-3 (Figure 1) details the RDAs for Calcium, Vitamin D, Magnesium, Potassium, Sodium, and Zinc. ◦ Clinical Note: These requirements vary by age and sex to meet specific metabolic needs.

MANAGEMENT & TREATMENT

• Protein Requirements: 1. Recommended Dietary Allowance (RDA): ~0.8 g/kg desirable body mass per day (assuming met energy needs and high biological value). 2. Biological Value: Highest for animal proteins, followed by legumes, cereals, and roots. 3. Optimization Strategy: Combinations of plant proteins can increase biological value and lower total protein intakes necessary to meet requirements. 4. Timing: Timing of protein intake over the course of the day has little effect. 5. Increased Needs: Required during growth, pregnancy, lactation, and rehabilitation after injury or undernutrition. • Fat Requirements: 1. Energy Content: 9 kcal/g. 2. Average Intake: 34% of calories. 3. Optimal Health Target: ≤ 30% of calories. 4. Saturated & Trans-fat: <10% of calories. 5. Polyunsaturated Fats: <10% of calories. 6. Monounsaturated Fats: Account for the remainder of fat intake. • Carbohydrate Requirements: 1. Energy Content: 4 kcal/g. 2. Average Intake: 45–55% of total calories. 3. Added Sugars: <10% (preferably <6%). 4. Tissue Specificity: Brain requires ~100 g glucose/day; other tissues require ~50 g/d. • Other Substances: 1. Alcohol: 7 kcal/g, but not a nutrient. • Water Requirements: 1. Standard Requirement: 1–1.5 mL per kilocalorie of energy expenditure. 2. Expected Losses: ◦ Feces: 50–100 mL/d ◦ Evaporation or Exhalation: 500–1000 mL/d ◦ Urine: ≥ 1000 mL/d 3. Adjustment for Increased Loss: ◦ Fever: +200 mL/d per °C ◦ Severe Diarrhea: up to 5 L/d • Energy Calculation (EER): 1. Calculate Resting Energy Expenditure (REE): ◦ Male: 900 + 10m ◦ Female: 700 + 7m (where m = mass in kilograms) 2. Apply Physical Activity Level (PAL) to determine EER: ◦ 1.4 (inactive) ◦ 1.6 (low active) ◦ 1.75 (active) ◦ 2.05 (very active) 3. Clinical Adjustment: ◦ For sedentary or low active individuals, use PAL of 1.2 to 1.4 to avoid overestimation. • Dietary Planning (Table 343-4): 1. Fruit Intake: 1.5–2.5 cups (depending on energy level). 2. Grain Intake: 5–10 oz eq (at least half should be whole grains). 3. Dairy Intake: 3 cups or 120–260 ozc. 4. Sodium Limit: <2300 mg at all energy levels.

SPECIAL POPULATIONS

• Pregnancy & Lactation: ◦ Requirement: Increased protein intake required. • Renal Insufficiency: ◦ Risk: Reduced tolerance to dietary protein due to uremia. • Liver Failure: ◦ Risk: Reduced tolerance to dietary protein; can precipitate encephalopathy.

Reference Tables

Harrison's 22e, p.2602

LIFE-STAGE
GROUP		 TOTAL WATERa
(L/d)		 CARBOHYDRATE
(g/d)		 TOTAL FIBER
(g/d)		 FAT
(g/d)		 LINOLEIC ACID
(g/d)		 `-LINOLENIC ACID
(g/d)		 PROTEINb
(g/d)
Infants
Birth to 6 mo 0.7* 60* NDc 31* 4.4* 0.5* 9.1*
6–12 mo 0.8* 95* ND 30* 4.6* 0.5* 11.0
Children
1.3* 130 19* ND 7* 0.7*
1.7* 130 25* ND 10* 0.9*
Males
9–13 y 2.4* 130 31* ND 12* 1.2* 34
14–18 y 3.3* 130 38* ND 16* 1.6* 52
19–30 y 3.7* 130 38* ND 17* 1.6* 56
31–50 y 3.7* 130 38* ND 17* 1.6* 56
51–70 y 3.7* 130 30* ND 14* 1.6* 56
>70 y 3.7* 130 30* ND 14* 1.6* 56
Females
2.1* 130 26* ND 10* 1.0*
2.3* 130 26* ND 11* 1.1*
2.7* 130 25* ND 12* 1.1*
2.7* 130 25* ND 12* 1.1*
2.7* 130 21* ND 11* 1.1*
2.7* 130 21* ND 11* 1.1*
Pregnant Women
14–18 y 3.0* 175 28* ND 13* 1.4* 71
19–30 y 3.0* 175 28* ND 13* 1.4* 71
31–50 y 3.0* 175 28* ND 13* 1.4* 71
Lactating Women
3.8* 210 29* ND 13* 1.3*
3.8* 210 29* ND 13* 1.3*
3.8* 210 29* ND 13* 1.3*

TABLE 343-4 Choose My Plate: A Guide to Individualized Dietary Planning

Harrison's 22e, p.2604

EXAMPLES OF STANDARD PORTION SIZES AT
INDICATED ENERGY LEVEL
DIETARY FACTOR, UNIT OF
MEASURE (ADVICE)		 LOWER:
1600 kcal		 MODERATE:
2200 kcal		 HIGHER:
2800 kcal
Fruits, cups (Focus on fruits.) 1.5 2 2.5
2 3
Grains, oz eq (Make at least half
of grains whole.)a		 5 7 10
5 6
Dairy, cups or ozc (Choose
calcium-rich foods.)		 3 3 3
120 260
Sodium, mg <2300 at all
energy levels