Growth is considered the gold standard tool and primary outcome measure of nutritional status in pediatrics (11, 13). Growth should be monitored at regular intervals throughout childhood and adolescence and measured every time a child presents, regardless of the health setting (i.e., preventive, acute, or chronic care) (5, 13). In this regard, anthropometric measurement is the initial critical component of all primary care routine well visits in pediatric clinical practice (18, 20). Accurately collecting and trending anthropometric data over time and reviewing age and gender-adjusted growth charts at every pediatric visit is essential in early recognition of failure to thrive (FTT), particularly a decline in weight percentile, and malnutrition (5, 12, 18).

Anthropometric measures of growth include weight for age (WFA), length for age (LFA), weight for length (WFL) in children under 2 years of age and head circumference up to 36 months of age, while standing height for age (HFA), WFA and body mass index (BMI) for age are typically collected after 2 years of age (12, 13, 21).

Based on anthropometric measurements, malnutrition can be classified as severe, moderate and mild (4, 8, 12) (Table 1).

Weight velocity (for children under 2 years; useful for early detection of abnormal growth patterns), head circumference (0–36 months; developmental delays may be associated with malnutrition), MUAC (in children aged ≥2 months), and TSFT (in children >12 months) are additional anthropometric parameters used to assess growth and development (11, 12, 22) (Table 1).

Although changes in growth percentiles are visually easy to interpret on a growth chart, current guidelines recommend using z-scores instead of percentiles for anthropometric assessments. Z-scores provide more precise information on a child's nutritional status by quantifying how far individual measurements deviate from population medians (5, 11–13, 23). A decline in z-scores—reflecting a greater negative deviation from the median—is associated with an increased risk of severe malnutrition (5).

When compared to WFL, WFH and BMI z-scores, MUAC z-scores are considered to be more sensitive to diagnose mild-to-moderate malnutrition and to track the change in nutritional status overtime, and also to provide more reliable data in the presence of ascites or edema, being not affected by fluid shifts or hydration status (24–26). Recently, MUAC z-score tape was developed to further facilitate the diagnosis of primary malnutrition which enables single-step assessment of nutritional status (as defined by z-score) without using ancillary reference charts and calculators, and for a larger number of children regardless of the any age and across a wide weight range (12, 26–28).

Currently accepted z-score ranges differentiate mild malnutrition (z-score −1 to −1.9), moderate malnutrition (z-score −2 to −2.9), and severe malnutrition (z-score ≤ −3), which can be further characterized as acute changes (<3 months) or chronic (>3 months) in duration (5, 29) (Table 1).

According to ASPEN recommendations, the diagnosis of pediatric malnutrition requires evidence of deterioration in at least one of the following indicators, assessed using data from two separate time points: weight gain velocity (for children aged <2 years), weight loss (for those aged >2 years), deceleration in weight-for-length or BMI-for-age z-scores, or inadequate nutrient intake (13, 30, 31) (Table 1). These criteria are applicable when multiple anthropometric data points are available over time, and a decline in any single indicator may be sufficient to establish the diagnosis of malnutrition.

In children with neurological disabilities, such as those with cerebral palsy (CP), the accuracy of anthropometric measurements is often compromised by factors like joint contractures, muscle atrophy, and movement disorders. These limitations reduce the reliability of standard anthropometric tools and may lead to misinterpretation of nutritional status (12, 32–34).

Furthermore, the commonly used cut-off values below −2 z-scores on standard growth charts for the healthy children—typically applied for nutritional assessment and malnutrition classification—may not be appropriate for children and adolescents with CP. This is due to differences in growth trajectories between children with CP and typically developing peers, which necessitates individualized interpretation and, in some cases, alternative growth references (13, 19, 35, 36).

Accordingly, nutritional assessment of children with neurological impairment is suggested to include the evaluation of body composition (assessment of body fat mass and muscle wasting) besides the weight and height measurements (37–39). Nutrition-focused physical exam (NFPE), including the evaluation of muscle and subcutaneous fat wasting, signs of oedema, oral health, suck, swallow/breathe ability, appetite and affect, is considered useful in providing supportive evidence to malnutrition in these children (38–41).

Developmental assessment and neurocognitive monitoring are recognized as key functional outcome measures in the context of malnutrition. In contrast, restricted growth and stunting are considered incomplete proxies for developmental delay, and should be interpreted with caution (5, 11, 31, 42).

In most cases, inadequate nutrient intake is related to non-illness causes such as lack of parental knowledge of appropriate feeding, patient feeding refusal or other maladaptive feeding behaviors, food insecurity, and less commonly parental abuse or neglect (18, 45). The remaining cases of inadequate nutrient intake are attributed to underlying organic medical conditions such as acute illness, gastrointestinal, endocrine, genetic and other systemic inflammatory disorders (18, 44) (Table 2) (Table 2).

The risk factors increasing the likelihood of underlying medical condition and hospitalization for evaluation and initial treatment in a malnourished child are history of prematurity and a more severe decline in weight/height z-score (z-score of <−3) (18, 46) (Table 2).

The underlying conditions in this category typically are gastrointestinal conditions that result in malabsorption, such as inflammatory bowel disease, celiac disease, food-protein allergy, exocrine pancreatic insufficiency such as cystic fibrosis, and other protein-losing enteropathies. These conditions can also all be exacerbated by nonorganic factors (18) (Table 2).

In this category, it is challenging to consume enough calories to meet the increased demand due to underlying chronic diseases such as CHD, CLD, CKD, anemia, malignancy, and chronic infectious diseases. Nonorganic factors can also exacerbate these conditions (18) (Table 2).

Nutritional support is the cornerstone of malnutrition treatment, with two primary goals: restoration of cellular function (short-term) and replenishment of lost tissue (long-term) (4, 47–49). The criteria for initiation and monitoring of nutritional support are summarized in Table 3 (1, 4, 49–52).

In children achieving a WFH ≥ −1 z score or ≥ 90% of the median WHO reference values under nutritional support, the progress is considered (4, 52). However, most children remain in the range of −1 to −2 z scores within the specified time limits (max 6 months) of the first nutritional support and they eventually regress to −3 z scores without continued nutritional support. Moreover, even in those with progress, there is a high risk of relapse of malnutrition (1, 4, 52).

Hence, the participating experts consider that current clinical nutrition practice only covers the children with established malnutrition, while those with mild malnutrition (−1 to −2 z scores) remain at risk of worsening to established malnutrition particularly in the setting of primary malnutrition, and those with chronic or severe malnutrition remain insufficiently treated given their need for a prolonged nutritional support. In general, adherence to nutritional product is higher in secondary malnutrition, while discontinuation rates are remarkably high in children with primary malnutrition who were prescribed with home nutritional support.

Accordingly, periodic monitoring of the child every 3–6 months during the first 2 years following recovery or discharge is essential. An effective strategy should also be implemented to track children who miss follow-up appointments, as they are at increased risk of malnutrition recurrence (1, 4, 52–54). At each visit, caregivers should be asked about the child's recent health status, feeding practices, and play activities, and the child should be thoroughly assessed for growth and developmental progress (1, 4, 52).

Malnourished children with a good appetite (documented to be taking at least 80% of the recommended daily oral supplement), and those without clinically noticeable medical complications are eligible for outpatient management with oral supplement support (55).

Conversely, those who have a poor appetite (consuming below the minimum standard) or present with complications should be referred and admitted for inpatient care or stabilization centers (55).

Children with severe acute malnutrition (SAM) and complications require hospitalization. The nutritional support principles are similar in primary and secondary malnutrition, which involves stabilization, active catch-up and nutritional rehabilitation. The inpatient care is discontinued when WFH/L z score or MUAC z score ≥ −2 and edema has completely resolved for at least 2 weeks (4, 55). Failure to regain appetite and weight or reduce edema are the criteria for declaring “failure to respond to treatment,” which requires extensive medical evaluation and return to the stabilization phase (4, 8, 55) (Table 4).

Appropriate nutritional intervention is a critical component in the management of malnutrition (9, 18, 56). Experts emphasize the following primary goals in the treatment of pediatric malnutrition:

Timely replenishment of protein, energy, and micronutrient deficits through individualized nutritional support tailored to each patient's specific needs, including the duration and method of intervention

Recommended energy intake for the healthy children and in those with specific underlying conditions is summarized in Table 5 (4, 22, 57–59).

Mild-to-moderate malnutrition is treated generally on an outpatient basis with increasing the amount of energy intake by 50%–100% of that recommended for the age-matched healthy children (57–59).

In infants, breastfeeding is continued along with enriched supplementary feeding and addition of enteral product when necessary (4, 57).

Daily energy requirement for catch-up growth in children with primary malnutrition is calculated based on the condition of the malnourished child with 1.2–2.0-fold higher energy intake than recommended for the healthy children (4, 58, 59) (Table 5).

In children with secondary malnutrition, energy requirement is determined based on the underlying disease with consideration of higher energy intake for hypermetabolic conditions (i.e., chronic disease, severe infection) and lower energy need in those with minimal activity (i.e., children with neurological disease, bed-ridden children) (4, 8) (Table 5).

In the general pediatric population, sufficient protein intake is necessary in infancy and early childhood periods to enable normal growth and development (22, 60).

As shown in Table 6, recommendations for protein intake in the pediatric population as well as the terminology related to nutrition vary depending on the issuing health authority. Dietary reference values (DRVs) and Dietary Reference Intakes (DRIs) are umbrella terms for a set of nutrient reference values. Estimated Average Requirement-EAR/Average Requirement-AR refers to the level of nutrient intake that is adequate for half of the people in a population group. Recommended Dietary Allowance-RDA/Population Reference Intake-PRI refers to the level of nutrient intake that is adequate for virtually all (97%–98%) people in a population group. Adequate Intake-AI refers to the average observed daily level of intake by a population group/groups of apparently healthy people that is assumed to be adequate. Tolerable Upper Intake Level-UL refers to the maximum amount of a nutrient that can be consumed safely over a long period of time), and Lower Threshold Intake-LTI refers to the level of intake below which almost all individuals will be unable to maintain “metabolic integrity”, according to the criterion chosen for each nutrient (60–66).

The Acceptable Macronutrient Distribution Range (AMDR) for protein is considered to be 5%–20% of total calories for children during 1–3 years of age and 10%–30% of total calories for children 4–18 years of age (67). As age increases, the protein content of the formula per 100 kcal generally increases, and lower calorie formulas have a higher percentage from protein. According to their caloric density, formulas are classified as low-/isocaloric (<0.9 kcal/mL), normocaloric/ (0.9–1.2 kcal/mL), and high energy (>1.2 kcal/mL) formulae (68, 69).

Accordingly, experts consider that the standard of care in pediatric malnutrition involves use of an energy and protein-rich formula, which is defined as the formula containing ≥1.2 kcal/mL and ≥ 4 gr protein/100 mL. Protein should constitute at least 10% of total calories (70, 71).

Nonetheless, it should be noted that beyond the dietary recommendations to prevent deficiency, there are no guidelines for an “optimal” protein intake in pediatric population for promoting healthy growth and development (60). In fact, protein intake trends in children and adolescents in Western Europe and United States are usually two- to three-fold higher than the dietary recommendations (60). The transition period to a family diet is considered a critical time window for protein intake, as usually characterized by a rapid increase of protein intake mainly due to the shift to cow's milk which has two times higher protein content (5.15 g/100 kcal) compared to infant formula (IF) or follow-on formulas (FOFs) (60, 72–74). This seems notable given that increased intakes exceeding the current recommended protein intake in the pediatric age group are considered likely to be causally related to an increased risk of obesity across one's lifespan (60, 73–75).

Hence, the European Food Safety Authority (EFSA) scientific opinion on the composition of IFs and FOFs recommended that the minimum level of protein in these formulas should remain at 1.8 g/100 kcal, but that the upper limit for protein content of FOFs should be reduced from 3.0 to 2.5 g/100 kcal (71, 76, 77).

However, these recommendations are based on the factorial method utilizing nitrogen balance studies, which tend to overestimate nitrogen intake and underestimate excretion, leading to a net positive balance and potentially underestimating the actual protein requirements of children and adolescents (60, 62, 78). Therefore, further research is needed to clarify critical time windows, define optimal protein intake ranges, and validate current protein intake guidelines in the pediatric population (60).

Although an increase in the energy density of foods and thus provision of adequate energy in diet is often achieved by increasing the lipid content, there is disturbed lipid metabolism in children with severe malnutrition (10, 79). While healthy children need approximately 30% of their daily energy intake from fat after the age of 2, the recommended amount is higher for malnourished children. The WHO recommends F75 with 32% of its total energy coming from fat at the beginning of malnutrition treatment while recommends F100, that has 53% of its total energy coming from fat, for the rehabilitation period (52). MCTs are easier to digest, absorb, and metabolize than LCTs, which makes them a preferable source of abundant and rapidly available energy in case of increased energy needs (i.e., undernourished patients after major surgery or children during normal or retarded growth) (10, 80–83). However, to avoid essential fatty acid deficiency, care should be taken to ensure that energy from long-chain fatty acids does not fall below 15%.

The recommended protein requirements for the pediatric critical care population (ASPEN Clinical Guidelines), children with normal growth, metabolism, body composition, and activity levels (National Academy of Sciences), and underweight infants and children requiring catch-up growth (National Research Council) are summarized in Table 7 (13, 63, 75, 84).

Enteral nutrition (EN) remains the preferred route of nutrient delivery in critically ill children and, whenever feasible, should be initiated within the first 24–48 h of pediatric intensive care unit (PICU) admission. Current guidelines (85) recommend that parenteral nutrition (PN) not be initiated during the initial 24 h of critical illness. In children with an adequate baseline nutritional status and considered to be at low risk of nutritional deterioration, initiation of supplemental PN should be deferred until at least one week after PICU admission. Conversely, in malnourished or high-risk children, PN may be considered within the first week of admission if sufficient advancement of EN cannot be achieved (Table 8). However, in recent years, data have emerged suggesting that early initiation of PN should not be considered, regardless of the child's nutritional status (86, 87). Protein provision should be initiated early in the course of critical illness, with a minimum target of 1.5 g/kg/day, acknowledging that higher intakes may be necessary in infants and younger children, as well as in those with more severe illness, to promote a positive protein and nitrogen balance. This should then be gradually increased as tolerated up toward 3 g/kg by the stage of recovery with appropriate provision of energy. The safety of protein intake >3 g/kg/d in children has not been demonstrated (85, 88). Similar to the recommendation to start PN late, there are also data suggesting that it would be better not to give protein in the acute phase of parenteral nutrition (87).

For protein and energy requirements for “optimal” catch-up growth; in the first step, it is necessary to decide what the ratio of fat and lean mass of the weight gain will be. Total body percent fat changes with age. If we want the desired catch-up growth to be 30% fat (normal total percent body fat of a 6-month-old infant) and 70% lean body mass (25% of which is protein), the additional energy requirement for 1 g of weight gain will be (0.3 × 9) + (0.7 × 0.25 × 4) = 3.4 kcal. If we aim for a 10 g/kg/day weight gain per day, we must provide 10 × 3.4 = 34 kcal/kg/day energy in addition to normal energy requirement (84, 89).

Similar calculations can be made for protein requirements. 20%–25% of lean body mass is protein. If we assume that the metabolic efficiency of dietary proteins is 70%, 0.36 g (0.25/0.7) protein should be taken for 1 g of lean body. If a 10 g/kg/day weight gain is planned, 3.6 g/kg protein should be given in addition to the maintenance protein requirement (84, 89).

Accordingly, as shown in Table 9, increasing nutritional needs (specific calorie and protein requirements) should be considered in certain disease groups associated with increased likelihood of malnutrition and growth delay, such as neurological disability, CKD, oncologic disease, CHD and cystic fibrosis (4, 5, 85, 88, 90–102).