Obesity and metabolic syndrome are now recognized as significant health concerns for survivors of pediatric Acute Lymphoblastic Leukemia (ALL) and are consequences of their treatment. The majority of weight gain occurs during the induction phase of therapy (first 28 days), when patients receive various chemotherapies in addition to high dose glucocorticoids. Physiological levels of glucocorticoids are required for metabolic control, but chronic exposure to elevated doses has been linked to metabolic disease including type 2 diabetes and obesity. Nutrition plays an important role in the development of obesity and is also amongst the few adjustable parameters in the treatment of pediatric ALL. We therefore determined if a diet high in omega‐3 fatty acids provided by fish oil can reduce the weight gain and metabolic syndrome phenotype associated chronic high dose glucocorticoid treatment. 3 week old C57BL/6 male mice were fed a “Western type” diet (45% calories from fat (lard) (HFL)) ad libitum. At 6 weeks of age, mice received the synthetic glucocorticoid, Prednisolone, at a dose of 40 mg/m2/day for 28 days. During the Prednisolone treatment, mice either remained on the HFL diet or were switched to an isocaloric diet containing 45% fat from fish oil (HFO). Body weight, food consumption, fat deposition in the liver, accumulation of epididymal adipose tissue and adipocyte size were determined. Mice on the HFO diet gained less weight during the treatment period (P = 0.03), with a dramatic decrease in fat deposition in the liver irrespective of glucocorticoid treatment. Epididymal adipose depots were smaller in mice consuming the HFO diet (P < 0.0001) with a concomitantly decrease in systemic Leptin levels (P = 0.05). Interestingly, glucocorticoid therapy caused a significant increase in adipocyte size when the mice are consuming the HFL diet (P = 0.001). The results from this study suggest that a dietary intervention in the form of fish oil during glucocorticoid treatment can reduce weight gain and metabolic syndrome and reduce long term consequences of ALL treatment.Support or Funding InformationFY16 Faculty Research Grant (University of Memphis)