In children who are 6–59 months of age, severe acute malnutrition is defined by a very low weight-for-height/weight-for-length, or clinical signs of bilateral pitting oedema, or a very low mid-upper arm circumference. Severe acute malnutrition affects an estimated 19 million children under 5 years of age worldwide and is estimated to account for approximately 400,000 child deaths each year.

Severely malnourished children requiring inpatient care have medical complications and are generally unable to tolerate usual levels of certain nutrients such as proteins, fats and sodium. Thus, standard inpatient management of severe acute malnutrition involves two phases:

• initial stabilization when life-threatening complications are treated
• nutritional rehabilitation when catch-up growth occurs

F-75, a low-protein milk-based formula diet, is given as the therapeutic food in the stabilization phase, followed by a gradual transition over two days or so (transition phase) to F-100, a milk formula with higher protein and energy content, in the rehabilitation phase. Ready-to-use therapeutic food (RUTF) has replaced liquid F-100 in the rehabilitation phase in a variety of settings where severe acute malnutrition is treated. Most RUTFs are lipid-based pastes combining milk powder, electrolytes and micronutrients and offer the malnourished child the same nutrient intake as F-100, with the addition of iron.

Many treatment settings currently implement a transition phase of feeding, during which, the amount of the rehabilitation diet, namely F-100 or RUTF, is introduced in carefully restricted amounts for several days, until ad libitum feeding is introduced. However, the optimal approach to transition phase feeding is unclear from practice.