Background: The utility of dairy ingredients in the supplementary foods used in the treatment of childhood moderate acute malnutrition (MAM) remains unsettled. Objective: We evaluated the effectiveness of a peanut-based readyto-use supplementary food (RUSF) with soy protein compared with a novel RUSF containing dairy ingredients in the form of whey permeate and whey protein concentrate in the treatment of children with MAM. Design: We conducted a randomized, double-blind clinical effectiveness trial involving rural Malawian and Mozambican children 6-59 mo of age with MAM treated with either soy RUSF or a novel whey RUSF treatment of w75 kcal $ kg 21 $ d 21 for up to 12 wk. Results: The proportion of children that recovered from MAM was significantly higher in the group that received whey RUSF (960 of 1144; 83.9%) than in the group that received soy RUSF (874 of 1086; 80.5%; P , 0.04; risk difference 3.4%, 95% CI: 0.3%, 6.6%). Children who consumed whey RUSF also demonstrated better growth markers, with a higher mean midupper arm circumference (MUAC) at the time of discharge (P , 0.009), greater MUAC gain during the course of treatment (P , 0.003), higher mean weight-forheight z score at discharge (P , 0.008), and greater weight gain (P , 0.05). No significant differences were identified in length gain or time to recovery between the 2 groups. Conclusion: This study highlights the importance of milk protein in the treatment of MAM, because the use of a novel whey RUSF resulted in higher recovery rates and improved growth than did soy RUSF, although the whey RUSF supplement provided less total protein and energy than the soy RUSF. This study was registered at clinicaltrials.gov as NCT01790048.Am J Clin Nutr 2016;103:926-33.