F75 and F100 diets

The management of Severe Acute Malnutrition (SAM) is physiologically divided into two distinct phases: the Stabilization Phase and the Rehabilitation Phase. This division is critical because the metabolic state of a child with SAM differs significantly between the acute, fragile state and the recovery state. Two specific therapeutic milk formulas, F-75 (Starter Diet) and F-100 (Catch-up Diet), have been designed by the WHO to meet the specific physiological needs of each phase.

1. F-75 (Starter Diet)

F-75 is the therapeutic diet used exclusively during the Stabilization Phase (usually Days 1–7) of SAM management.

Purpose and Physiological Rationale

• Metabolic Fragility: In the initial phase, the child's body is in a state of "reductive adaptation," meaning vital systems have slowed down to survive on minimal intake. The liver cannot metabolize high protein loads, and the heart is weak.
• Goal: The primary goal is not weight gain but to restore metabolic functions, correct electrolyte imbalances, and prevent death from hypoglycemia or refeeding syndrome.
• Composition Rationale: F-75 is low in protein (0.9 g/100 mL) and energy (75 kcal/100 mL) to avoid overloading the liver (which cannot process excess nitrogen/ammonia) and the kidneys (limited ability to excrete solute load). It is designed to prevent "refeeding syndrome," which can be fatal if high calorie/protein feeds are introduced too early.

Nutritional Composition (per 100 mL)

• Energy: 75 kcal.
• Protein: 0.9 g.
• Lactose: 1.2–1.3 g (Low lactose to prevent osmotic diarrhea).
• Osmolarity: Low osmolarity (approx. 334–413 mOsm/L) to prevent osmotic shifts and diarrhea.
• Micronutrients: It must be fortified with a Combined Mineral Vitamin (CMV) mix containing potassium, magnesium, and other trace elements. Iron is strictly excluded during this phase as free iron promotes bacterial growth and oxidative stress in the unstable child.

Administration Guidelines

• Frequency: Small, frequent feeds are essential to prevent hypoglycemia and gastric overload. Ideally given every 2 hours (12 feeds/day) initially.
• Volume:
  • Standard: 130 mL/kg/day.
  • Severe Edema (+++): Restricted to 100 mL/kg/day to prevent fluid overload and heart failure.
• Route: Oral feeding using a cup and spoon is preferred. Nasogastric (NG) tubes are used if the child is too weak to swallow or takes <80% of the prescribed amount.

Standard Recipes (Preparation for 100 mL and 1000 mL)

There are two main types of F-75: Milk-based and Cereal-based. Cereal-based F-75 has lower osmolarity and is preferred for children with persistent diarrhea.

[Sources: 232, 361, 434]

2. F-100 (Catch-up Diet)

F-100 is the therapeutic diet used during the Rehabilitation Phase (usually from Week 2 onwards) after the child has stabilized, regained appetite, and lost edema.

Purpose and Physiological Rationale

• Rebuilding Tissues: Once metabolic machinery is restored, the body needs high energy and protein to rebuild wasted muscle and fat.
• Goal: To achieve rapid catch-up growth (weight gain of >10 g/kg/day).
• Composition Rationale: F-100 is energy-dense (100 kcal/100 mL) and high in protein (2.9 g/100 mL) to support rapid tissue accretion. It contains significantly more calories and protein than breast milk or standard formula to bridge the massive nutrient gap.

Nutritional Composition (per 100 mL)

• Energy: 100 kcal.
• Protein: 2.9 g (approx. 3 times that of F-75).
• Lactose: ~4.2 g (Higher than F-75; use caution in severe lactose intolerance).
• Osmolarity: Approx. 419 mOsm/L.
• Micronutrients: Similar fortification with electrolytes and vitamins. Iron is added in this phase (if not already in the CMV/pre-mix) to treat anemia and support tissue synthesis.

Administration Guidelines

• Transition: F-100 is introduced gradually. The standard protocol involves replacing F-75 with an equal volume of F-100 for 2 days (48 hours) before increasing volume, to avoid a sudden metabolic load.
• Frequency: Feeds are reduced to every 4 hours (6 feeds/day).
• Volume: The goal is free feeding (ad libitum). The target intake increases to 150–220 kcal/kg/day (approx. 150–220 mL/kg/day).
• Weight Gain Monitoring: Daily weight gain is monitored. Good weight gain is >10 g/kg/day; moderate is 5–10 g/kg/day; poor is <5 g/kg/day.

Standard Recipes (Preparation for 100 mL and 1000 mL)

[Sources: 233, 440]

3. Comparison of F-75 and F-100

[Sources: 232, 233, 296, 361, 363]

4. Transition Protocol (Step 8 of SAM Management)

Moving from F-75 to F-100 is a critical period where the child is monitored for tolerance (signs of refeeding syndrome like heart failure).

1. Readiness Criteria: Return of appetite, resolution/reduction of edema, and control of infection.
2. Procedure:
   • Replace F-75 with the same amount of F-100 for 48 hours (2 days).
   • If well tolerated, increase each successive feed by 10 mL until some food is left uneaten.
3. Monitoring: Watch for rapid breathing or rapid pulse (signs of fluid overload/heart failure). If these occur, reduce the volume or revert to F-75.

5. Practical Notes on Preparation

• Measurement: Accurate measurement is crucial. Using a marked container is better than adding a fixed volume of water, as the final volume must be exactly 100 mL or 1000 mL to maintain correct caloric density.
• Hygiene: Feeds must be prepared freshly. If refrigeration is available, they can be stored for 24 hours; otherwise, they should be used within a few hours to prevent bacterial contamination.
• Local Alternatives: If commercial F-75/F-100 packs are not available, they can be prepared using local milk, sugar, oil, and cereal powder as per the recipes above. Micronutrient solution (CMV) must be added (20 mL per 1000 mL of diet).