The majority of immune development and the ability to ‘tolerate’ food proteins occurs after birth, during the period when most infants’ are consuming human milk. The omega-3 long chain polyunsaturated fatty acid, docosahexaenoic acid (DHA), is required for immune function but Canadian have one of the lowest contents of DHA in their breast milk in the world. The content of this fatty acid is highly variable in breast milk and depends primarily on dietary intake. Using information from the analysis of DHA in breast milk in our Alberta Pregnancy Outcomes and Nutrition (APrON) cohort and work from our neonatal clinical trials, we have designed pre-clinical studies in rodents to determine the importance of DHA in breast milk for the development of both immune function and immune tolerance. Our studies have demonstrated both in health and food allergy susceptible rodents that feeding additional DHA to moms during lactation have both immediate and lifelong (programing) effects on the development of the offspring’s immune system. This is important as the Dietary Reference committee is currently reviewing the dietary recommendations for omega-3 fatty acids.