Chapter 343: Nutrient Requirements and Dietary Assessment¶
Chapter 343 | Part 10: Disorders of the Gastrointestinal System
KEY CLINICAL POINTS¶
- Estimated Energy Requirement (EER) is calculated using resting energy expenditure (REE) and physical activity level (PAL), with formulas adjusted for age, sex, weight, and activity level.
- Protein requirements are ~0.8 g/kg desirable body mass/day for adults, with higher needs during growth, pregnancy, lactation, and recovery from illness.
- Dietary Reference Intakes (DRIs) include Recommended Dietary Allowances (RDAs) and Adequate Intakes (AIs) to guide nutrient intake for different populations.
- Excessive nutrient intake can lead to toxicity, with tolerable upper levels (ULs) established to prevent adverse effects.
- Nutritional assessment involves evaluating dietary intake, biochemical markers, anthropometric measurements, and clinical status to identify malnutrition risks.
1. DEFINITION & OVERVIEW¶
Nutrient requirements are essential for maintaining health, with deficiencies leading to growth impairment, metabolic dysfunction, and organ failure. Nutrients include macronutrients (protein, fat, carbohydrates) and micronutrients (vitamins, minerals). Energy needs are balanced by total energy expenditure (TEE), which includes resting energy expenditure (REE) and physical activity.
Table 343-1: Dietary Reference Intakes (DRIs) for Vitamins and Minerals¶
| Nutrient | RDA (mg/day) | AI (mg/day) |
|---|---|---|
| Vitamin A | 700-900 | 700 |
| Vitamin C | 75-90 | 75 |
| Vitamin D | 600-800 | 600 |
| Vitamin B12 | 2.4 | 2.4 |
| Iron | 8-18 | 8 |
Table 343-2: Dietary Reference Intakes (DRIs) for Macronutrients¶
| Macronutrient | RDA (g/day) | AI (g/day) |
|---|---|---|
| Protein | 0.8 g/kg body weight | 0.8 g/kg body weight |
| Fat | 20-35% of calories | 20-35% of calories |
| Carbohydrate | 45-65% of calories | 45-65% of calories |
1.1 Nutrient Classification¶
Essential nutrients (e.g., 9 amino acids, 13 vitamins, 13 minerals) must be obtained from diet. Conditionally essential nutrients may be synthesized under specific conditions. Macronutrients provide energy (protein 4 kcal/g, fat 9 kcal/g, carbohydrates 4 kcal/g).
1.2 Energy Balance¶
Estimated Energy Requirement (EER) maintains energy balance. For adults, average intake is ~2600 kcal/day for men and 1800 kcal/day for women. Energy intake must match total energy expenditure (TEE) to maintain weight.
2. EPIDEMIOLOGY¶
Nutritional deficiencies are prevalent in populations with limited access to diverse diets, malabsorption disorders, or chronic diseases. Risk factors include poverty, aging, and certain medical conditions (e.g., renal failure, liver disease).
Table 343-3: DRIs for Total Water and Macronutrients¶
| Life-Stage Group | Total Water (L/d) | Carbohydrate (g/d) | Protein (g/d) |
|---|---|---|---|
| Infants (0-6 mo) | 0.7 | 60 | 9.1 |
| Infants (6-12 mo) | 0.8 | 95 | 11.0 |
| Children (1-3 y) | 1.3 | 130 | 13 |
| Children (4-8 y) | 1.7 | 130 | 19 |
2.1 Demographics¶
Infants, elderly, and individuals with chronic illnesses (e.g., diabetes, HIV) are at higher risk for nutrient inadequacy. Obesity and malnutrition coexist in populations with poor dietary patterns.
2.2 Nutrient-Specific Risks¶
Sodium excess is linked to hypertension; excessive saturated fats contribute to cardiovascular disease. Micronutrient deficiencies (e.g., vitamin D, iron) are common in populations with limited sunlight exposure or poor dietary diversity.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Nutrient deficiencies arise from inadequate intake, malabsorption, or increased requirements. Chronic diseases (e.g., renal failure, liver disease) alter nutrient metabolism and excretion. Dietary patterns, socioeconomic factors, and medical conditions influence nutrient status.
Table 343-4: Choose My Plate Portion Sizes¶
| Dietary Factor | Lower (1600 kcal) | Moderate (2200 kcal) | Higher (2800 kcal) |
|---|---|---|---|
| Fruits (cups) | 1.5 | 2 | 2.5 |
| Vegetables (cups) | 2 | 3 | 3.5 |
| Grains (oz eq) | 5 | 7 | 10 |
| Protein (oz eq) | 5 | 6 | 7 |
3.1 Malabsorption Mechanisms¶
Conditions like celiac disease, inflammatory bowel disease, and pancreatic insufficiency impair nutrient absorption. Gastrointestinal losses (e.g., diarrhea, vomiting) exacerbate deficiencies.
3.2 Metabolic Alterations¶
In chronic diseases, energy needs may decrease due to reduced lean body mass. Protein-calorie malnutrition (PCM) occurs in severe undernutrition, leading to muscle wasting and immune dysfunction.
4. CLINICAL FEATURES¶
Clinical manifestations of nutrient deficiencies include fatigue, weight loss, anemia, and organ dysfunction. Excess intake may cause toxicity (e.g., vitamin A toxicity, hypernatremia).
Table 343-5: Nutrient Toxicity Thresholds¶
| Nutrient | Toxic Dose (mg/day) | Symptoms |
|---|---|---|
| Sodium | 2000-3000 | Hypertension, edema |
| Vitamin A | 50000 | Hepatotoxicity, teratogenicity |
| Iron | 200 | Gastrointestinal bleeding, organ failure |
4.1 Deficiency Syndromes¶
Iron-deficiency anemia, vitamin D deficiency rickets, and scurvy (vitamin C deficiency) are classic examples. Pellagra (niacin deficiency) presents with dermatitis, diarrhea, and dementia.
4.2 Excess Symptoms¶
Hypernatremia from excessive sodium intake, hypervitaminosis A, and metabolic alkalosis from excessive bicarbonate intake are potential complications.
5. DIFFERENTIAL DIAGNOSIS¶
Nutrient deficiencies must be differentiated from other conditions causing similar symptoms (e.g., anemia due to chronic disease vs. iron deficiency). Laboratory tests and dietary history are critical for accurate diagnosis.
5.1 Anemia Differentiation¶
Iron-deficiency anemia vs. vitamin B12/folate deficiency anemia: serum iron, ferritin, and vitamin levels help distinguish. Hemolytic anemia may mimic nutritional deficiencies.
5.2 Metabolic Disorders¶
Thyroid dysfunction, diabetes, and renal disease can mimic nutrient-related symptoms. Biochemical markers (e.g., serum albumin, BUN) aid in differentiation.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnostic tools include dietary assessment, biochemical tests (e.g., serum albumin, iron studies), and anthropometric measurements. Nutritional screening tools like GLIM criteria help identify at-risk patients.
Table 343-6: Nutritional Screening Tools¶
| Tool | Criteria | Use Case |
|---|---|---|
| GLIM | Weight loss, BMI, muscle mass, dietary intake | Acute care settings |
| MNA | Eating habits, mobility, weight change | Elderly patients |
6.1 Laboratory Tests¶
Serum albumin, prealbumin, ferritin, vitamin levels, and electrolytes are key. Urinary nitrogen and creatinine clearance assess protein catabolism.
6.2 Nutritional Screening¶
GLIM criteria evaluate weight loss, BMI, muscle mass, and dietary intake. The Mini Nutritional Assessment (MNA) is used in elderly populations.
7. MANAGEMENT & TREATMENT¶
Nutritional management involves dietary modifications, supplementation, and addressing underlying causes. Enteral/parenteral nutrition is used in severe cases. Monitoring and follow-up are essential to prevent recurrence.
Table 343-7: Nutrient Supplementation Guidelines¶
| Deficiency | Supplement | Dosage |
|---|---|---|
| Iron deficiency | Iron sulfate | 60-200 mg/day |
| Vitamin D deficiency | Cholecalciferol | 1000-2000 IU/day |
| Vitamin B12 deficiency | Cyanocobalamin | 1000 mcg/day |
7.1 Dietary Interventions¶
Increase intake of fruits, vegetables, whole grains, and lean proteins. Limit saturated fats, added sugars, and sodium. Tailor diets to individual needs (e.g., renal diets, diabetic diets).
7.2 Supplementation¶
Vitamin and mineral supplements are used for deficiencies. Parenteral nutrition is reserved for patients with severe malabsorption or inability to eat.
8. PROGNOSIS & COMPLICATIONS¶
Early intervention improves outcomes. Complications include organ failure, infections, and mortality in severe cases. Long-term follow-up is needed to prevent recurrence and manage chronic conditions.
8.1 Complications of Deficiency¶
Severe protein-calorie malnutrition leads to cachexia, immune dysfunction, and increased infection risk. Micronutrient deficiencies may contribute to chronic diseases (e.g., osteoporosis, cardiovascular disease).
8.2 Long-Term Outcomes¶
Nutritional rehabilitation improves quality of life but requires sustained dietary adherence. Chronic conditions like diabetes and renal disease necessitate lifelong dietary management.
9. SPECIAL CONSIDERATIONS¶
Special populations (e.g., pregnant women, elderly, children) have unique nutrient needs. Cultural, socioeconomic, and medical factors influence dietary compliance and outcomes.
Table 343-8: Nutrient Requirements in Pregnancy¶
| Nutrient | RDA (mg/day) | AI (mg/day) |
|---|---|---|
| Folate | 600 | 600 |
| Iron | 27 | 27 |
| Calcium | 1000 | 1000 |
| Vitamin D | 15 | 15 |
9.1 Pregnancy and Lactation¶
Increased protein, iron, and calcium needs. Folate and vitamin D supplementation is critical. Lactating women require additional calories and nutrients for milk production.
9.2 Elderly Patients¶
Reduced total-body water, decreased appetite, and medication interactions increase risk of malnutrition. Nutrient-dense, easy-to-swallow diets are recommended.
10. KEY POINTS & CLINICAL PEARLS¶
Nutritional assessment is critical for diagnosing and managing deficiencies. Use DRIs and screening tools to guide interventions. Tailor dietary plans to individual needs and monitor for complications.