Children need more energy and protein per kilogram than adults because they are growing. Any illness that reduces intake, blocks absorption, raises needs, or disturbs metabolism shows up first as faltering growth. This topic covers undernutrition and faltering growth, obesity, malabsorption, key micronutrient deficiencies, and the nutrition side of metabolic diseases. Newborn screening disorders are introduced in Unit 3 ("Inborn Errors of Metabolism"); diabetes is covered in "Endocrine Disorders."

Faltering growth (failure to thrive) — inadequate weight gain for age, for example weight below the 2nd–3rd percentile or falling across two major percentile lines. Almost always the final pathway is not enough calories taken in, absorbed, or retained. Causes include feeding difficulties, poverty and food insecurity, disturbed caregiver–child interaction or neglect, and medical conditions (heart disease, GERD, CF, celiac disease, chronic kidney disease). Old labels "organic" vs "non-organic" are less useful because causes usually mix.

Acute malnutrition (WHO)

• Severe acute malnutrition (SAM) in children 6–59 months: weight-for-height below −3 SD, or mid-upper arm circumference (MUAC) under 115 mm, or bilateral pitting edema (kwashiorkor)
• Marasmus: severe wasting of fat and muscle, "old man" face; kwashiorkor: edema, skin and hair changes, enlarged fatty liver, linked to poor diet quality and infection (the exact cause is not fully understood)
• Stunting (height-for-age below −2 SD) reflects chronic undernutrition, especially in the first 1,000 days (conception to age 2)

Obesity — BMI-for-age: overweight 85th to below 95th percentile; obesity at or above the 95th percentile; severe obesity at or above 120% of the 95th percentile. Obesity is a chronic disease driven by genetics, environment, sleep, screen time, food marketing, and social factors. It brings type 2 diabetes, hypertension, dyslipidemia, fatty liver disease, sleep apnea, slipped capital femoral epiphysis, and depression and bullying.

Malabsorption

• Cystic fibrosis: blocked pancreatic ducts → no pancreatic enzymes reach the gut → fat and protein malabsorption and loss of fat-soluble vitamins A, D, E, K
• Celiac disease: villous atrophy (see "Gastrointestinal Disorders")

Micronutrient deficiencies

• Vitamin D deficiency → rickets: soft bones, bowed legs, widened wrists, delayed fontanel closure, hypocalcemia. Breast milk contains little vitamin D
• Vitamin A deficiency: night blindness, xerophthalmia, higher death rate from measles and diarrhea
• Iron deficiency (see "Hematologic Disorders")

Metabolic diseases with nutritional treatment

Anthropometry — plot weight, length/height, head circumference (to age 2–3), and BMI (from age 2) on growth charts at every visit. Use WHO charts from birth to 2 years and CDC or WHO charts after that, depending on country policy. Trends matter more than a single point.

Faltering growth — treat the cause; energy-dense feeds (concentrated formula only as prescribed, added fats); structured meals and snacks; dietitian, feeding therapist, and social work input; hospital admission when safety or severe malnutrition is a concern.

SAM — ready-to-use therapeutic food (RUTF) at home for children with appetite and no complications; hospital care for complications: treat hypoglycemia, hypothermia, and infection (antibiotics routinely), rehydrate slowly with low-sodium ORS (ReSoMal), IV fluids only for shock (risk of heart failure), and start feeding slowly (F-75 formula) to avoid refeeding syndrome, then catch-up feeding.

Obesity (AAP 2023)

• Family-based intensive health behavior and lifestyle treatment as early as possible — the most effective first approach; the whole family changes eating, activity, sleep, and screen habits
• Weight-loss medication may be offered from age 12 with obesity, alongside lifestyle treatment
• Referral for metabolic and bariatric surgery evaluation from age 13 with severe obesity
• Avoid weight stigma; screen for depression and disordered eating; crash diets, skipped meals, and fasting are harmful

CF — pancreatic enzyme replacement with all meals and snacks, high-calorie high-fat diet, CF-specific fat-soluble vitamins, extra salt.

Rickets prevention and treatment — vitamin D 400 IU daily for breastfed and partially breastfed infants starting in the first days of life; treatment doses for deficiency plus calcium.

PKU — phenylalanine-restricted diet (low-protein natural foods plus phenylalanine-free medical formula) for life; avoid aspartame (it contains phenylalanine); sapropterin helps some children. Women with PKU need tight control before and during pregnancy to protect the fetus.

Galactosemia — lifelong elimination of lactose and galactose; soy formula; monitor development, cataracts, and (in girls) ovarian failure.

Congenital hypothyroidism — levothyroxine started as soon as possible after diagnosis, dose adjusted to thyroid tests as the child grows.

Hypoglycemia (conscious child) — fast-acting carbohydrate first (about 0.3 g/kg; commonly 10–15 g glucose tablets, juice, or regular soda), recheck glucose in 15 minutes, repeat if still low, then a snack. Unconscious or unable to swallow: glucagon (IM, SC, or nasal) or IV dextrose — nothing by mouth.

Drug safety (doses weight-based and verified against a pediatric reference)

Listed in priority order.

1. Physiologic safety
   • Hypoglycemia: if the child is conscious and can swallow, give fast-acting sugar immediately, then check glucose; unconscious → glucagon or IV dextrose, side-lying position
   • SAM: prevent hypothermia (skin-to-skin, covers) and hypoglycemia (frequent feeds day and night); watch for refeeding syndrome (low phosphate, potassium, magnesium; weakness, edema, heart failure) and fluid overload during rehydration
   • Galactosemia: stop all milk feeds as soon as the result is reported; watch for sepsis
2. Accurate measurement
   • Weigh on the same scale, unclothed infants; measure length on a length board; plot every measurement
   • Calorie counts and intake records
3. Feeding assessment and support
   • Observe a full feeding: position, latch or bottle technique, duration, cues, and caregiver–child interaction
   • Consistent caregiver at feeds; quiet environment; model positive feeding behaviors
4. Family-centered obesity care
   • Use person-first, nonjudgmental language ("a child with obesity"); set small, specific goals with the whole family
5. Medication and diet teaching (see Education)
6. Safeguarding — when neglect is suspected, document objectively and follow reporting rules

• Obesity: family meals, water instead of sugar-sweetened drinks, more fruits and vegetables, at least 60 minutes of physical activity daily, limit recreational screen time, adequate sleep, no TV in the bedroom; do not single out the child — the whole family changes
• PKU: special formula for life; weigh and count phenylalanine; avoid high-protein foods (meat, fish, eggs, dairy, nuts, legumes) and aspartame; regular blood tests
• Galactosemia: read labels for milk, lactose, whey, casein; some medicines contain lactose
• Levothyroxine: every day for life, never skip; give as taught; attend thyroid tests
• Vitamin D drops for breastfed infants; vitamin A supplementation where offered by national programs
• Hypoglycemia: recognize early signs; always carry fast-acting sugar; do not skip meals; teach the "15-minute recheck"
• Breastfeeding exclusively for about 6 months, then iron-rich and diverse complementary foods

• Faltering growth: observe an actual feeding and keep a diet record first; weight falls before length and head size
• SAM: MUAC under 115 mm, weight-for-height below −3 SD, or bilateral edema; start feeding slowly to prevent refeeding syndrome
• Obesity: BMI at or above 95th percentile; family-based lifestyle treatment first; medication from 12, surgery evaluation from 13 (severe obesity); no fasting or crash diets
• CF: pancreatic insufficiency → fat-soluble vitamins A, D, E, K and enzymes with every meal
• PKU: lifelong phenylalanine-restricted diet with special formula; avoid aspartame
• Galactosemia: no breast milk or lactose formula — soy or lactose-free formula
• Levothyroxine: same time daily, consistent with feeds, not mixed in a bottle, away from soy, iron, calcium
• Conscious hypoglycemic child: fast-acting sugar first, recheck in 15 minutes; unconscious → glucagon
• Vitamin D 400 IU daily for breastfed infants
• In DKA, potassium falls with insulin — monitor closely