Nutritional Disorders

Core Concepts

How the Body Uses Food

Carbohydrates are broken into sugars for quick energy; protein is broken into amino acids used to build and repair tissue; fat is broken into fatty acids for energy storage and cell function. Vitamins and minerals act as helpers in these reactions. The gut does the processing: the mouth chews and starts starch digestion, the stomach mixes and begins protein digestion, the small intestine absorbs most nutrients (with pancreatic enzymes and liver bile), and the large intestine reabsorbs water. When any step fails — poor intake, vomiting, malabsorption, increased losses, or increased demand from illness — nutritional status declines.

Undernutrition and Malnutrition

Undernutrition ranges from mild weight loss to severe malnutrition. It can be primary (not enough food available or eaten — poverty, swallowing problems, depression, dementia, dental problems, restrictive diets) or secondary (the body cannot use what is eaten — cancer, chronic infection, malabsorption, or increased metabolic demand). Two classic severe forms, seen historically in famine and still seen in some settings, are marasmus (severe calorie deficiency with wasting of muscle and fat) and kwashiorkor (protein deficiency with edema, even when some calories are eaten). For today's hospital nurse the principle is simple: unexplained weight loss, poor appetite, or muscle wasting in any patient is a flag worth acting on, whatever their weight.

Micronutrient Deficiencies

Specific vitamin and mineral deficiencies produce recognizable problems, though in practice they often overlap with general malnutrition:

• Iron deficiency causes anemia — fatigue, weakness, pale skin — because iron is needed to make hemoglobin, the oxygen-carrying protein in red blood cells.
• Vitamin B12 deficiency (from poor intake or the stomach's inability to absorb the vitamin, as in some GI conditions) causes anemia and nerve problems, including numbness and tingling.
• Folate deficiency also causes anemia and is especially important in pregnancy, affecting fetal development — which is why folate supplementation is routine in prenatal care.
• Vitamin D deficiency affects calcium balance and bone health; it is common with little sun exposure and in older adults.
• Iodine deficiency affects thyroid hormone production and was historically a leading cause of goiter (thyroid enlargement).

This is a study guide, not a dosing reference: screening, diagnosis, and supplementation decisions belong to providers and registered dietitians, and lab values are facility-specific.

Overnutrition and Obesity

Overnutrition is the modern epidemic: too many calories relative to needs, stored as fat. Obesity is classified by body mass index (BMI, weight relative to height), though BMI alone is a rough tool that does not capture muscle mass, body composition, or where fat is carried. Obesity is linked to type 2 diabetes, hypertension, heart disease, sleep apnea, joint problems, and increased surgical risk — and it is a chronic condition, not a character flaw. Nursing care involves respectful communication (person-first language, no assumptions about effort or willpower), supporting weight-management plans made with the person and their care team, and coordinating with dietitians and other specialists.

The Nurse's Nutrition Assessment

A practical nutrition assessment includes: weight trends (recent unintentional weight loss is more meaningful than a single number), appetite and intake, swallowing (coughing or choking with meals suggests dysphagia and aspiration risk), physical signs (muscle wasting, poor wound healing, oral health), and functional changes (weakness, fatigue, declining ability to eat independently). Many facilities use a nutrition screening tool (for example, the Malnutrition Universal Screening Tool or similar) to identify risk systematically. The nurse does not diagnose malnutrition — the nurse screens, observes, documents, reports, and refers to the registered dietitian, who performs the full assessment and develops the nutrition plan with the provider.

Supporting Intake at the Bedside

Everyday nursing actions improve nutrition: positioning the patient upright for meals, providing assistance and adaptive utensils, offering smaller frequent meals for poor appetite, honoring food preferences and cultural needs when possible, addressing dental pain or swallowing problems, and treating the causes of poor intake (nausea, pain, constipation). When oral intake is not enough or not possible, the next steps are enteral nutrition (feeding through a tube into the gut, e.g., nasogastric or gastrostomy) or parenteral nutrition (intravenous feeding) — both covered in their own file in this chapter, Parenteral and Enteral Nutrition.

Common Confusions