DESCRIPTION

• Globally, the World Health Organization (WHO) identifies malnutrition in three main forms: undernutrition, micronutrient-related malnutrition with deficiency or excess, and overweight/obesity with associated diet-related noncommunicable diseases like diabetes or heart disease. Undernutrition includes low weight for age (underweight), low height for age (stunting), and low weight for height (wasting). As undernutrition is corrected, there may be higher risk for overweight and obesity, which is addressed in a separate chapter.
• In 2013, the American Society for Parenteral and Enteral Nutrition (ASPEN) defined malnutrition “as an imbalance between nutrient requirement and intake, resulting in cumulative deficits of energy, protein, or micronutrients that may negatively affect growth, development, and other relevant outcomes.”
• This definition considers the etiology as either “illness-related malnutrition” (secondary to disease or injury) or “non–illness-related malnutrition” (secondary to environmental or behavioral factors). Malnutrition may be classified as acute (<3 months in duration), which primarily affects weight, or chronic (>3 months), which can lead to stunting.
• The 2023 WHO guidelines expand from management of children 6 to 59 months of age to include infants <6 months at risk for poor growth and development with emphasis on care of the mother–child dyad, post-exit interventions after recovery, and prevention.
• There are two clinical presentations of severe acute malnutrition (SAM): kwashiorkor and marasmus.
  • Kwashiorkor (nutritional edema) is characterized by severe protein deficiency, varying degrees of wasting and/or stunting, bilateral pitting edema, and dermatosis.
  • Marasmus results from a deficiency of total energy (calories) and protein, leading to wasting.
  • The distinction between kwashiorkor and marasmus may be blurred, and features of both may be present as marasmic kwashiorkor.

EPIDEMIOLOGY

• Undernutrition underlies 45% of childhood mortality in those <5 years of age worldwide.
• Most with acute malnutrition live in Asia and Africa.
• Global hunger was declining in most parts of the world but increased with the COVID-19 pandemic. The estimated number of children with stunting <5 years of age was 149 million and 45 million with wasting in 2022. The 2022 Global Nutrition Report noted 3.4% of children <5 years of age had stunting and 0.1% had wasting in the United States.
• The highest prevalence in those with malnutrition are <1 year old.

ETIOLOGY

• Several theories have been proposed regarding the etiology of kwashiorkor with its characteristic edema, but more recent studies suggest that protein deficiency and oxidant stress with free radical damage may be sequelae rather than causes.
• Studies suggest a link between the gut microbiome and poor diet resulting in kwashiorkor.

RISK FACTORS

• Increased nutritional needs in chronic disease, malabsorption causing increased losses, decreased intake in the setting of behavioral or psychosocial issues, or medical conditions that cause feeding difficulties such as congenital anomalies
• Lack of sanitation, poor hygiene, poverty, racism, and food insecurity are contributing factors. Availability of resources and their allocation as determined by social, cultural, political, and environmental factors like war and climate change also affect malnutrition.
• Kwashiorkor has been described in chronic malabsorptive conditions such as cystic fibrosis, but such cases are rarer as treatments for underlying diseases and direct causes of malabsorption like pancreatic enzyme replacement have become standards of care.
• Cases may be from neglect or undiagnosed disease.
• Consumption of protein-deficient milk alternatives, sugar water, or juice can be due to poor caregiver knowledge about nutrition, perceived milk or formula intolerance, or food fads causing malnutrition.

GENERAL PREVENTION

Thorough prevention would require examination of accessibility, availability, and affordability of nutritious food, access to health providers to screen for risk factors, establishment of national safety nets for child health, and the deconstruction of systemic racism and social constructs that have developed over time.

PATHOPHYSIOLOGY

• Reduced basal metabolic rate
• Impaired temperature regulation, leading to hypothermia in a cold environment and hyperthermia in a hot environment
• Increased total-body sodium and decreased total-body potassium and phosphorus
• Protein synthesis, including albumin, transferrin, and apolipoprotein B, is reduced. Decreased fat transport causes fatty infiltration of the liver. Reduced hepatic metabolism can impair toxin excretion.
• Early rapid gluconeogenesis, followed by impaired gluconeogenesis (risk of hypoglycemia) and use of fat stores for energy, resulting in lipolysis and ketosis, and then protein use (visceral proteins in kwashiorkor and musculature in marasmus)
• Reduced cardiac output leads to low blood pressure, compromised tissue perfusion, reduction in renal blood flow, and decreased glomerular filtration rate.
• Diminished inspiratory and expiratory pressures and vital capacity
• Reduction of gastric and pancreatic secretions and intestinal motility
• Intestinal mucosal atrophy resulting in malabsorption of carbohydrates, fats, and vitamins
• Hormonal changes: increased growth hormone secretion and levels of glucagon, epinephrine, and cortisol, low circulating insulin and serum triiodothyronine (T₃) and thyroxine (T₄) levels, and reduced somatomedin activity
• Thinning of cerebral cortex due to decreased numbers of neurons, synapses, and myelinations, leading to slowed brain growth and neurocognitive changes
• Immune system
  • Atrophy of lymph glands, tonsils, and thymus with diminished T-cell function, increasing susceptibility to infection
  • Serum immunoglobulins are typically normal or increased, although enteral immunoglobulin A (IgA) is decreased in experimental models of SAM.
  • Diminished gut barrier function in setting of luminal bacterial overgrowth may allow bacterial translocation. Breakdown of skin and respiratory mucosal barriers can increase risk of infections.
  • Delayed wound healing may be seen with nutritional deficiencies.
  • Typical signs of infection, such as leukocytosis and fever, may be absent.