Nutrition supplies energy, builds and repairs tissue, and regulates body processes. Malnutrition — undernutrition or overnutrition — delays wound healing, weakens immunity, increases falls and pressure injuries, and lengthens hospital stays. Nurses are often the first to spot a nutrition problem.
Energy-yielding nutrients
| Nutrient | kcal per gram | Main roles |
|---|
| Carbohydrate | 4 | Main energy source; spares protein from being burned for energy; prevents ketosis; fiber aids bowel function |
| Protein | 4 | Tissue growth and repair, enzymes, hormones, antibodies, plasma proteins (oncotic pressure) |
| Fat | 9 | Concentrated energy, absorption of fat-soluble vitamins, insulation, cell membranes |
| Alcohol | 7 | Energy without nutrients ("empty calories") |
Vitamins, minerals, and water provide no energy.
Carbohydrates: glucose is the brain's preferred fuel, but during prolonged fasting the brain can also use ketone bodies. Dietary fiber has no caloric value in the usual sense but lowers LDL cholesterol (soluble fiber) and adds stool bulk (insoluble fiber).
Proteins: made of amino acids. Essential (indispensable) amino acids cannot be made by the body and must come from food. Current references list nine essential amino acids for adults as well as children — histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. (Older texts listed eight for adults and added histidine only for infants.) A complete (high-quality) protein supplies all essential amino acids in adequate amounts — animal proteins and soy; plant proteins can be combined (e.g., rice with legumes).
Fats: the essential fatty acids — linoleic acid (omega-6) and alpha-linolenic acid (omega-3) — cannot be made by the body. Saturated and trans fats raise cardiovascular risk.
Vitamins
- Fat-soluble: A, D, E, K — stored in liver and fat, so toxicity is possible with excess supplements
- Water-soluble: B complex and C — not stored in large amounts, excess excreted in urine, so regular intake is needed
| Deficiency | Classic sign |
|---|
| Vitamin A | Night blindness, dry eyes |
| Vitamin D | Rickets (children), osteomalacia (adults) |
| Vitamin K | Bleeding, prolonged clotting time |
| Thiamine (B₁) | Beriberi, Wernicke encephalopathy (alcohol use disorder) |
| Vitamin B₁₂ / folate | Megaloblastic anemia (B₁₂ also neuropathy); folate deficiency → neural tube defects |
| Vitamin C | Scurvy — bleeding gums, poor wound healing |
Minerals: major (calcium, phosphorus, magnesium, sodium, potassium, chloride) and trace (iron, zinc, iodine, selenium). Calcium and phosphorus form bone and teeth; iron carries oxygen in hemoglobin; zinc supports wound healing; iodine is needed for thyroid hormone.
Water is the most essential nutrient: solvent for metabolic reactions, transport, temperature regulation, and lubrication. Adults need roughly 30–35 mL/kg/day unless restricted.
Protein-energy malnutrition
- Marasmus — chronic deficit of total energy: severe wasting of fat and muscle, "skin and bones," serum albumin often near normal
- Kwashiorkor — inadequate protein with relatively adequate calories, often with acute stress: edema, enlarged fatty liver, low albumin, skin and hair changes (the flag sign — alternating bands of normal and depigmented hair)
- Marasmic kwashiorkor — features of both
A full nutrition assessment follows ABCD: Anthropometric, Biochemical, Clinical, and Dietary data.
Anthropometric
- Weight and height at every admission, using the same scale and time of day for trends
- Body mass index (BMI) = weight (kg) ÷ height (m)²
| BMI (kg/m²), WHO adult categories | Classification |
|---|
| < 18.5 | Underweight |
| 18.5–24.9 | Normal |
| 25.0–29.9 | Overweight |
| ≥ 30.0 | Obesity |
WHO suggests lower Asian action points: BMI ≥ 23 increased risk and ≥ 27.5 high risk (some Asian guidelines use ≥ 25 as obesity). In children and adolescents, BMI is interpreted by age- and sex-specific percentiles (WHO or CDC growth charts), not adult cutoffs.
- Unintentional weight loss is one of the most important findings: more than 5% in 1 month, 7.5% in 3 months, or 10% in 6 months is clinically significant (severe) weight loss. % weight change = (usual weight − current weight) ÷ usual weight × 100.
- Waist circumference reflects abdominal (visceral) fat: increased risk at > 102 cm (40 in) in men and > 88 cm (35 in) in women by US criteria; for Asian populations the thresholds are ≥ 90 cm in men and ≥ 80 cm in women.
- Triceps skinfold thickness estimates fat stores; mid-upper arm circumference (MUAC) is simple, cheap, and noninvasive — it reflects combined fat and muscle and is widely used to screen children and adults for malnutrition.
Clinical (physical signs)
- Loss of subcutaneous fat (orbital, triceps, ribs) and muscle wasting (temples, clavicles, shoulders, thighs)
- Edema or ascites (can hide weight loss)
- Hair: dull, thin, easily plucked, flag sign; skin: dry, flaky, poor turgor, slow healing, bruising
- Mouth: cracked lips (cheilosis), glossitis, bleeding gums
- Reduced grip strength and functional capacity
Dietary
- 24-hour recall, food frequency, food records, calorie counts
- Appetite, chewing and swallowing, nausea, food access, cultural and religious practices, alcohol use, supplements
Screening vs. assessment
- Screening (within 24 hours of admission in most hospitals) identifies clients at risk — e.g., Malnutrition Screening Tool, MUST, NRS-2002. A positive screen triggers referral to a dietitian.
- Mini Nutritional Assessment (MNA) is designed for older adults.
- Subjective Global Assessment (SGA) uses history (weight change, intake change, GI symptoms, function) and physical exam (fat loss, muscle wasting, edema). It rates clients A = well nourished, B = moderately (or suspected) malnourished, C = severely malnourished. SGA does not use laboratory values.
- Current diagnostic frameworks (the ASPEN/Academy of Nutrition and Dietetics characteristics and the GLIM criteria) diagnose malnutrition from weight loss, low BMI or reduced muscle mass, reduced intake, and disease burden or inflammation.
Laboratory values — interpret with caution
| Test | Normal (adult) | Notes |
|---|
| Serum albumin | 3.5–5.0 g/dL (35–50 g/L) | Half-life about 3 weeks; falls with inflammation, liver disease, and fluid overload — a marker of illness severity rather than a reliable measure of nutrition |
| Prealbumin (transthyretin) | About 15–36 mg/dL (150–360 mg/L) | Half-life 2–3 days; also falls in inflammation |
| Transferrin / TIBC | TIBC about 250–450 mcg/dL (45–81 µmol/L) | Transferrin and TIBC decrease in protein malnutrition (but rise in iron deficiency) |
| Total lymphocyte count | Reduced in malnutrition | Nonspecific |
| Hemoglobin | Low in iron, B₁₂, folate deficiency | |
| C-reactive protein | Elevated with inflammation | Helps explain low albumin |
Because albumin and prealbumin fall during any acute illness, current guidance no longer uses them alone to diagnose malnutrition; weight history, intake, and physical findings are more reliable. Very low albumin (below about 2.5–3.0 g/dL) still signals high risk of complications.
Energy needs
- Indirect calorimetry — measures O₂ consumption and CO₂ production and is the most accurate way to determine energy expenditure in hospital
- Estimates: predictive equations (e.g., Mifflin-St Jeor) or about 25–30 kcal/kg/day for many adults; protein about 0.8 g/kg/day in health and higher (often 1.2–2.0 g/kg/day) in illness, wounds, or critical care
- Dietitian referral for positive screens, poor intake, wounds, or special diets
- Therapeutic diets ordered by the provider: clear liquid (broth, clear juice, gelatin), full liquid (adds milk, cream soups, ice cream), mechanical soft or pureed (chewing or swallowing problems), and modified diets such as sodium-restricted, carbohydrate-consistent, renal, or high-protein
- Swallowing evaluation by a speech-language pathologist when dysphagia is suspected; texture-modified diets and thickened liquids as ordered
- Oral nutrition supplements, and enteral or parenteral nutrition when oral intake is inadequate (see Nutritional Support)
Supplement safety
| Supplement | Safety points |
|---|
| Vitamin A | High doses are teratogenic — avoid excess in pregnancy; toxicity causes liver damage and raised intracranial pressure |
| Vitamin D | Toxicity → hypercalcemia (nausea, confusion, kidney stones) |
| Vitamin K | Reverses warfarin — keep intake consistent rather than avoiding leafy greens |
| Iron (oral) | Constipation, nausea, dark green-black stools; absorbed best with vitamin C on an empty stomach; separate from antacids, calcium, tetracyclines, and levothyroxine; accidental overdose is dangerous in children — store securely |
| Folic acid | 400 mcg (0.4 mg) daily for everyone who could become pregnant, continued in early pregnancy; higher doses after a previous pregnancy affected by a neural tube defect; can mask B₁₂ deficiency anemia |
- Screen every client on admission and whenever condition changes; refer positive screens.
- Weigh accurately and consistently; report unintended loss or rapid gain (rapid gain usually means fluid).
- Protect the airway during meals for clients with dysphagia: upright 90° if possible, chin tuck as taught, small bites, supervise, keep upright 30 minutes after meals.
- Monitor intake (percentage of meals eaten, calorie counts) and document intake and output.
- Create conditions for eating: oral care before meals, pain and nausea control before meals, clean environment, glasses and dentures in place, assistance with tray setup, protected mealtimes.
- Offer preferred and culturally acceptable foods, small frequent meals, and nutrient-dense snacks for clients with poor appetite.
- Collaborate with the dietitian and speech-language pathologist; reassess weekly.
- Balanced diet based on the national food guide; plenty of vegetables, fruits, whole grains, and lean protein; limit sugary drinks, sodium, and saturated fat.
- Read food labels for serving size, sodium, sugar, and fat.
- Supplements are not a substitute for food; fat-soluble vitamins can accumulate to toxic levels.
- Adequate fluid intake unless restricted.
- Older adults: report unplanned weight loss, poor appetite, and chewing problems early.
| Finding | Concern |
|---|
| Unplanned loss > 5% in 1 month or > 10% in 6 months | Significant malnutrition |
| BMI < 18.5 with muscle wasting | Undernutrition |
| Coughing or choking with meals, wet voice | Dysphagia and aspiration risk |
| Edema with low albumin and poor intake | Protein deficiency, fluid shifts |
| Poor wound healing, frequent infections | Protein, zinc, or vitamin C deficiency |
| Confusion, unsteady gait, eye movement abnormalities in heavy alcohol use | Thiamine deficiency — give thiamine before glucose |
- Carbohydrate 4, protein 4, fat 9, alcohol 7 kcal/g; vitamins, minerals, and water supply no energy
- Fat-soluble vitamins A, D, E, K can accumulate to toxic levels; vitamin C is water-soluble
- BMI = kg ÷ m²; normal 18.5–24.9
- Significant weight loss: > 5% in 1 month, > 10% in 6 months
- SGA rates A (well nourished), B (moderate), C (severe) using history and exam — no labs
- MNA is designed for older adults
- Albumin reflects inflammation and fluid status, not just nutrition; prealbumin has a shorter half-life (2–3 days)
- TIBC/transferrin fall in protein malnutrition
- Triceps skinfold = fat stores; MUAC = simple, noninvasive screening
- Indirect calorimetry is the most accurate measure of energy expenditure
- Kwashiorkor = edema and low albumin; marasmus = severe wasting
- Nine essential amino acids for adults (histidine included)
Country Notes
United States
- The Dietary Guidelines for Americans (updated every 5 years) and MyPlate are the national food guidance tools.
- Hospitals accredited by The Joint Commission must screen nutrition status on admission within a defined time frame.
Philippines
- "Pinggang Pinoy" (Food and Nutrition Research Institute) is the national healthy-plate guide, and Philippine Dietary Reference Intakes set nutrient targets.
- The ASIN Law (Republic Act 8172) requires salt iodization to prevent iodine deficiency.
- Both undernutrition (stunting, wasting) and rising overweight and obesity coexist; apply the Asian BMI and waist action points above or the local clinical guideline when classifying adults.