Clinical meaning
Nutrition is the process by which the body ingests, digests, absorbs, transports, utilizes, and excretes nutrients necessary for cellular metabolism, tissue repair, growth, and immune function. Macronutrients (carbohydrates, proteins, and fats) provide energy measured in kilocalories: carbohydrates yield 4 kcal/g and serve as the primary energy source; proteins yield 4 kcal/g and provide amino acids essential for tissue synthesis, enzyme production, and immune function; fats yield 9 kcal/g and are critical for cell membrane integrity, hormone synthesis, fat-soluble vitamin absorption (A, D, E, K), and insulation. Micronutrients (vitamins and minerals) serve as cofactors for enzymatic reactions, antioxidant defense, and structural components of tissues. Malnutrition develops when nutrient intake is insufficient to meet metabolic demands, resulting in progressive depletion of body stores. Protein-energy malnutrition manifests in two classic forms: marasmus (chronic caloric deficiency with severe muscle and fat wasting but preserved albumin levels) and kwashiorkor (acute protein deficiency with preserved fat stores, edema from low oncotic pressure, and hypoalbuminemia). In clinical practice, mixed forms are most common. Malnutrition impairs wound healing by reducing collagen synthesis, impairs immune function by decreasing lymphocyte...