When Cicely Williams published her 1933 paper in the Archives of Disease in Childhood describing a syndrome she had observed in Ghanaian children characterised by oedema, skin depigmentation, fatty liver, and growth failure, she named it “kwashiorkor” - the word used by the Ga people of the Gold Coast to describe the disease suffered by a child displaced from the breast by a new sibling. Williams had identified what would eventually be classified as the most severe protein-deficient form of protein-energy malnutrition, a condition that would occupy nutritional science, paediatric medicine, and global health policy for the following nine decades. Her observations predated the coinage of the term “protein-energy malnutrition” itself - that came in the 1960s - but they established the epidemiological reality that continues to shape health outcomes across Sub-Saharan Africa: that the consequences of inadequate dietary protein and energy are not merely matters of weight and height, but of immune function, organ integrity, brain development, and survival.

Defining Protein-Energy Malnutrition

Protein-energy malnutrition (PEM) is an umbrella term encompassing a spectrum of conditions arising from inadequate intake, impaired absorption, or excessive loss of dietary protein and/or total energy. The term captures both macronutrient dimensions simultaneously because in the diets of most low-income populations, energy and protein deficits tend to co-occur and are difficult to disentangle clinically. Although the term has been criticised for obscuring the distinct pathophysiology of protein versus energy deficit - and for oversimplifying what is almost always a compound deficiency involving micronutrients as well - it retains utility as a clinical and epidemiological category describing the spectrum from mild underweight to life-threatening severe acute malnutrition.

Bhutta et al. (2013) placed PEM within the broader architecture of undernutrition, distinguishing it from micronutrient deficiency while acknowledging that in practice the two rarely present alone. The 2013 Lancet Nutrition Series estimated that undernutrition in its various forms - including PEM, micronutrient deficiencies, and intrauterine growth restriction - collectively underlies approximately 45 per cent of under-five deaths globally.

Clinical Spectrum

Mild and Moderate Undernutrition

The largest portion of the PEM burden exists in a clinically subtle zone. Children with mild or moderate PEM may present with weight-for-age or weight-for-height z-scores between −1 and −2 standard deviations below the WHO median - below average but above thresholds for formal clinical designation. Subclinical deficits at this level are associated with higher susceptibility to infectious disease and slower recovery from infection, even when no acute clinical syndrome is present. Pelletier et al. (1995) demonstrated that mild-to-moderate malnutrition exerts a multiplicative effect on infection-related mortality risk - meaning the majority of malnutrition-associated deaths occur in children who are not severely malnourished, simply because the population carrying mild and moderate deficits vastly outnumbers those with severe wasting.

This epidemiological insight has important programme implications. If severe acute malnutrition accounts for a minority of attributable deaths, then therapeutic feeding programmes targeting only the severe end of the spectrum - however clinically appropriate - cannot on their own address the full mortality burden. Prevention-oriented approaches acting across the whole distribution of nutritional status are necessary complements.

Severe Acute Malnutrition: Marasmus

Marasmus - derived from the Greek for “withering” - is the non-oedematous form of severe acute malnutrition. It results primarily from prolonged energy deficit with relative preservation of protein intake, though both are usually depleted. The body progressively catabolises adipose tissue and then skeletal muscle to meet basal metabolic demands, resulting in the characteristic appearance of a child with almost no subcutaneous fat, visible ribs, and skin that hangs in loose folds from limbs and buttocks. The “old man’s face” - sunken cheeks and temporal wasting - and the “baggy pants” appearance of skin folds at the buttocks are clinical hallmarks.

Despite dramatic physical appearance, a child with uncomplicated marasmus often retains alertness and appetite - a clinically important distinction from kwashiorkor, where appetite suppression is frequent and neurological apathy is common. The presence of appetite is used operationally in CMAM protocols to distinguish children who can be managed in outpatient settings (those who pass the RUTF appetite test) from those requiring inpatient stabilisation.

Severe Acute Malnutrition: Kwashiorkor

Kwashiorkor presents the more complex pathophysiology. Its cardinal feature is bilateral pitting oedema - fluid accumulation in the interstitial spaces, extending from the feet upward in severe cases to affect the face, arms, and abdomen. Multiple mechanisms have been proposed to explain oedema in the context of malnutrition, and none is universally accepted as definitive. The classical hypoalbuminaemia theory - that low serum albumin reduces oncotic pressure, allowing fluid to shift from the vascular to interstitial compartment - has been challenged by observations that albumin levels do not consistently correlate with oedema severity. Alternative hypotheses include free radical damage from inadequate antioxidant micronutrients (particularly glutathione precursors), disruption of sodium-potassium pump function, and impaired hepatic protein synthesis beyond albumin alone. The metabolic basis of kwashiorkor is explored in clinical detail at Kwashiorkor and Marasmus: Clinical Features, Pathophysiology, and Management .

Skin changes in kwashiorkor include flaky paint dermatosis - areas of dark hyperpigmentation that crack and peel - and flag sign in hair, where alternating pale and dark bands reflect episodic nutritional adequacy and deficiency. Fatty liver arises from impaired synthesis of the lipoproteins needed to export accumulated triglycerides, and is often clinically detectable as hepatomegaly.

Metabolic Consequences of PEM

Muscle Wasting and Lean Mass Depletion

The body’s response to prolonged energy deficit follows an ordered sequence of catabolism. Glycogen stores are depleted within 24 hours; adipose tissue follows over days to weeks; skeletal muscle is mobilised as a substrate of last resort, releasing amino acids for gluconeogenesis and acute-phase protein synthesis. In severe malnutrition this process is far advanced: the child’s lean mass is substantially depleted, resting metabolic rate is suppressed, and the capacity for catch-up growth is constrained by the extent of muscle loss.

Prentice et al. (2013) reviewed the hormonal mediators of this catabolic cascade, highlighting suppression of insulin-like growth factor-1 (IGF-1), growth hormone resistance, low thyroid hormones (T3 and T4), and elevated cortisol as characteristic of the metabolic adaptation to undernutrition. These endocrine disruptions compound lean mass loss and impair the anabolic response to refeeding, explaining why catch-up growth is slower and less complete than nutritional rehabilitation alone would predict.

Hypoalbuminaemia and Acute-Phase Response

Serum albumin is synthesised exclusively in the liver, and its production depends on adequate amino acid supply. In severe protein deficiency, albumin synthesis falls; circulating albumin levels below 30 g/L are common in kwashiorkor, and levels below 20 g/L indicate critical protein depletion. Beyond its role in oncotic pressure maintenance, albumin serves as a transport protein for fatty acids, hormones, calcium, bilirubin, and many drugs - meaning hypoalbuminaemia has systemic metabolic consequences beyond fluid balance.

The liver simultaneously upregulates synthesis of acute-phase proteins (C-reactive protein, fibrinogen, ferritin) as part of the inflammatory response to concurrent infection and metabolic stress. This diversion of synthetic capacity away from albumin towards acute-phase reactants accelerates the decline in oncotic albumin levels.

Immune Impairment

Immune function depends on rapid cell proliferation and protein synthesis - processes that are severely curtailed in the context of PEM. T-lymphocyte counts fall, delayed hypersensitivity responses are blunted, and complement levels decline. The secretory IgA response at mucosal surfaces - the first line of defence against enteric pathogens - is impaired, increasing vulnerability to gastrointestinal and respiratory infections. Phagocyte function deteriorates, reducing the capacity to clear bacterial infections even when complement is adequate.

Guerrant et al. (2008) described the vicious cycle between gut pathology, nutrient malabsorption, and immune suppression in detail, establishing that environmental enteric dysfunction - subclinical gut inflammation driven by repeated exposure to faecal pathogens - independently compromises immune and nutritional status in SSA populations. Children living without access to safe water and adequate sanitation face repeated cycles of enteric infection that both precipitate PEM and prevent recovery from it.

The clinical consequence of immune impairment in PEM is a dramatic increase in case fatality rates from common childhood infections. Measles in a severely malnourished child carries a case fatality rate 400–800 times higher than in a well-nourished child; similarly elevated fatality rates apply to malaria, pneumonia, and invasive bacterial infections. It is through this potentiation of infection-mortality that PEM exerts most of its demographic impact.

Micronutrient Co-Deficiencies

PEM almost never presents in isolation from micronutrient deficiency. Diets that are inadequate in protein and energy are virtually always inadequate in zinc, iron, vitamin A, folate, iodine, and B-complex vitamins. Black et al. (2013) estimated that vitamin A deficiency alone contributes to approximately 670,000 under-five deaths annually, overlapping substantially with the population affected by PEM. Zinc deficiency, present in the majority of children with SAM, compounds immune impairment and specifically disrupts gut mucosal integrity, accelerating the malabsorption-malnutrition cycle.

This co-occurrence has important therapeutic implications: treating the protein-energy deficit without addressing micronutrient deficiencies produces incomplete recovery. Ready-to-use therapeutic food (RUTF) was specifically formulated to correct multiple micronutrient deficits simultaneously alongside macronutrient repletion. The interaction between zinc, iron, vitamin A, and the immune response during refeeding is reviewed further in the context of supplementation programmes at The Role of Micronutrient Interventions in Reducing Malnutrition .

PEM Across the Life Course

Intrauterine and Early Postnatal Origins

PEM does not begin at weaning. Maternal undernutrition before and during pregnancy reduces placental nutrient transfer, constraining foetal growth and producing intrauterine growth restriction (IUGR). Low birth weight - defined as below 2,500 g at term - is both a consequence of maternal PEM and a risk factor for PEM in the child, through reduced nutritional reserves at birth, compromised immune function, and reduced breastfeeding success.

Victora et al. (2010) described the intergenerational transmission of undernutrition, demonstrating in cohort data from five LMICs that women who were stunted as children give birth to smaller, more vulnerable infants - perpetuating the cycle across generations. This intergenerational dimension places PEM within a framework that extends well beyond individual dietary management to encompass adolescent girl nutrition, antenatal care, and social determinants of poverty.

The First 1,000 Days

The period from conception through 24 months of age - the “first 1,000 days” - represents the developmental window in which nutritional insults have the most profound and the least reversible consequences. During this period, brain growth is at its most rapid, the microbiome is established, immune programming is completed, and critical windows for physical growth are open. PEM during this window disrupts all of these processes concurrently.

Exclusive breastfeeding for the first six months provides complete nutritional protection against PEM in the absence of maternal malnutrition, while simultaneously conferring immune protection through secretory IgA, lactoferrin, and bioactive compounds. The transition to complementary feeding at six months is a period of particular vulnerability: most complementary foods in SSA are low-energy, low-protein porridges that cannot meet the infant’s growing nutrient demands. The interaction between infant feeding practices and PEM incidence is documented extensively in the programme literature from WASH Nutrition and community infant and young child feeding (IYCF) programmes across the region.

Long-Term Consequences

Children who survive severe PEM face a trajectory of adverse long-term outcomes even when clinical recovery appears complete. Neurodevelopmental consequences include reduced cognitive test scores, impaired school performance, and - in the case of kwashiorkor - specific deficits in language development and executive function that persist into adolescence. Physical consequences include reduced adult height, lower lean mass, and, paradoxically, increased risk of metabolic syndrome (insulin resistance, abdominal adiposity, hypertension) in later life - a manifestation of the developmental programming induced by early nutrient deprivation and subsequent nutritional transition.

The pathways between early malnutrition and adult non-communicable disease operate through epigenetic modifications, altered metabolic set-points, and the mismatch between a thrifty phenotype programmed for scarcity and an adult environment of caloric abundance. Victora et al. (2010) provided longitudinal evidence from the COHORTS collaboration confirming that low height-for-age at two years predicted lower adult height, educational attainment, and income, as well as higher risk of overweight and hypertension in adulthood.

Rehabilitation: Phases and Principles

Stabilisation Phase

The stabilisation phase of SAM treatment addresses the immediate physiological priorities: correcting metabolic emergencies (hypoglycaemia, hypothermia, dehydration), managing infections, and avoiding the dangers of refeeding syndrome. The WHO 10-step protocol for inpatient stabilisation recommends F-75 therapeutic milk - providing 75 kcal and 0.9 g protein per 100 ml - at this stage. High protein and high energy loads are specifically avoided in Phase 1 because the severely malnourished child cannot metabolise them safely: electrolyte shifts (particularly potassium and phosphate) during rapid refeeding can precipitate cardiac arrhythmias and death.

Iron supplementation, counterintuitively, is withheld during the stabilisation phase because free iron in the presence of bacterial infection can potentiate sepsis. It is introduced only during the rehabilitation phase when the child is clinically stable. Vitamin A is given as a high-dose supplement on admission, given the near-universal co-deficiency.

Rehabilitation Phase

The rehabilitation phase transitions to F-100 or RUTF - higher energy and protein formulations - to support catch-up growth. Catch-up growth rates of 10–20 g/kg/day are achievable with adequate nutritional and medical support, substantially exceeding normal infant growth rates. Stimulation - play, cognitive engagement, emotional interaction - is now recognised as an essential component of rehabilitation, given the pervasive effects of severe malnutrition on neurodevelopmental trajectories. The therapeutic milieu of stabilisation centres that includes structured play alongside nutritional rehabilitation has shown superior developmental outcomes compared to nutritional rehabilitation alone in randomised trial data.

Manary & Sandige (2008) reviewed the evidence for community-based rehabilitation with RUTF, concluding that for uncomplicated SAM the community setting achieves outcomes equivalent to hospital-based rehabilitation with major gains in coverage and reach. Collins et al. (2006) established the foundational programme evidence for this model at scale in SSA.

Follow-Up and Relapse Prevention

Discharge criteria - MUAC above 125 mm, absence of oedema, and two consecutive weeks of weight gain - mark the transition from therapeutic to follow-up care. Relapse rates of 10–20 per cent within twelve months of discharge are commonly reported; they are highest in children discharged to households with persistent food insecurity. Linking therapeutic feeding discharge to enrolment in supplementary feeding programmes, and to social protection transfers where available, is the most evidence-supported approach to reducing relapse, though operational integration between these programme streams remains inconsistent across SSA countries.

Epidemiological Burden in Sub-Saharan Africa

Across Sub-Saharan Africa, prevalence estimates from Demographic and Health Surveys and MICS surveys reveal a stark north-south gradient in acute PEM burden: the highest rates of severe and moderate wasting cluster in the Sahel (Niger, Chad, Mali, Burkina Faso), the Horn (Somalia, Ethiopia, South Sudan, Kenya), and conflict-affected countries (Central African Republic, DRC). Southern and middle Africa generally show lower acute malnutrition rates but often higher stunting burdens. For a broader epidemiological framing of malnutrition types and national statistics, see Malnutrition: Definition, Types, Causes, and Global Statistics .

The economic costs of PEM extend far beyond health systems. Lost cognitive potential translates to reduced educational attainment and adult productivity; increased illness burden raises healthcare expenditure; premature adult mortality reduces workforce participation. World Bank estimates suggest that undernutrition costs SSA economies 2–3 per cent of GDP annually through these channels - a figure that substantially understates the social cost by excluding the welfare effects on families and communities directly affected.

Limitations

This review draws primarily on programme data, cohort studies, and reviews from the published literature; randomised controlled trial evidence on specific aspects of PEM management - particularly the optimal protein-to-energy ratio during catch-up growth and the relative contributions of individual micronutrients to recovery - remains limited. The pathophysiology of kwashiorkor, despite nine decades of research, is not fully resolved: the relative contributions of hypoalbuminaemia, free radical damage, and sodium-potassium pump dysfunction to oedema formation remain contested. Epidemiological estimates of PEM burden rely on anthropometric surveys with variable quality and coverage; national estimates mask substantial within-country heterogeneity by wealth, rural-urban location, and agro-ecological zone. Long-term developmental follow-up data are sparse, particularly for populations in which severe malnutrition is treated at community level outside research settings.

FAQ

What is the difference between marasmus and kwashiorkor in PEM? Marasmus results primarily from severe energy deficiency and presents as profound wasting of muscle and fat with no oedema; affected children are typically alert and hungry. Kwashiorkor results primarily from protein deficiency and presents with bilateral pitting oedema, skin and hair changes, fatty liver, and often appetite loss and apathy. Both are classified as severe acute malnutrition. The two syndromes can coexist in the same child (marasmic-kwashiorkor), producing combined features.

Why does protein-energy malnutrition increase the risk of dying from infections? PEM impairs multiple arms of the immune system simultaneously: T-lymphocyte counts fall, mucosal secretory IgA is reduced, phagocyte function deteriorates, and complement levels decline. A malnourished child cannot mount an effective immune response to bacterial or viral infection, and cannot tolerate the metabolic demands of fever and acute inflammation. The result is that infections which a well-nourished child would survive readily - measles, pneumonia, diarrhoea - carry dramatically elevated case fatality rates in the context of PEM.

Can children recover fully from severe protein-energy malnutrition? Clinical recovery - defined as return to normal weight-for-height and resolution of oedema - is achievable in the majority of children with adequate treatment. Full neurodevelopmental recovery is less certain: severe or repeated malnutrition during the first two years of life, when brain growth is most rapid, can produce lasting cognitive and language deficits. Growth catch-up in height is partial at best. Adult metabolic risk, including insulin resistance and hypertension, is elevated even in those who appeared to recover clinically as children.

What role do micronutrient deficiencies play in protein-energy malnutrition? Micronutrient deficiencies almost always co-occur with PEM. The most consequential are zinc (impairs immunity and gut integrity), vitamin A (essential for immune function and epithelial barrier), iron (necessary for haemoglobin and immune cell function), and iodine (critical for brain development). Standard therapeutic foods such as RUTF are micronutrient-fortified specifically to address these concurrent deficits. Treating macronutrient deficiency alone without correcting micronutrient deficits produces incomplete recovery.

Dr. Amara Osei is a research fellow in global health nutrition. This article is part of an academic archive on nutrition in Sub-Saharan Africa.