Background: Childhood acute lymphoblastic leukemia (ALL) is the most common pediatric malignancy. The onset of obesity during childhood ALL has been well established and is associated with inferior survival rates and increased treatment-related toxicities. This pilot study sought to determine if a dietary intervention is feasible and minimizes weight gain during the initial phases of treatment for ALL. Methods: Participants were recruited from four institutions, fluent in English or Spanish, between 5-21 years old, and enrolled within three days of starting induction therapy. Participants were counseled for six months to follow a low glycemic diet. Dietary and anthropometric data were collected at baseline, end of induction, and end of month six (NCT03157323). Results: Twenty-three of 28 participants (82.1%) were evaluable and included in the analysis. Dietary intake of several nutrients targeted by the nutrition intervention declined (sugar, P = 0.003 and glycemic load, P = 0.053). We also observed a persistent increase in total vegetables across each timepoint (P = 0.015) and by the end of the intervention (P = 0.033). Importantly, we did not observe an increase in body mass index z-score during induction or over the six-month intervention period. Most families found the nutrition intervention easy to follow (60%) and affordable (95%) despite simultaneous initiation of treatment for ALL. Conclusions: A six-month nutrition intervention initiated during the initial phase of treatment for childhood ALL is feasible and may prevent weight gain. Our preliminary findings need to be confirmed in a larger clinical trial.