Breadfruit is a traditional staple crop from Pacific islands with the potential to improve worldwide food security and mitigate diabetes. Flour produced from breadfruit is a gluten-free, low glycemic index, nutrient dense and complete protein option for modern foods but basic scientific knowledge of health impacts of a breadfruit-based diet in animals and humans was lacking. We designed a series of studies to provide basic and fundamental data on impacts of a breadfruit-based diet through an in vitro and in vivo model. Cooked breadfruit flour was digested through a multi-stage enzyme digestion model to estimate protein digestibility in comparison to wheat flour. Breadfruit protein was found to be easier to digest than wheat protein in the enzyme digestion model. The flour digestions were applied to Caco-2 cells to test the cytotoxicity and to measure the immunogenicity through cytokine expression. No significant differences were observed for immune factors and cytokines (IL-4, IL-10, IL-8, TNF-α, IFN-γ) on Caco-2 cells between the breadfruit and wheat groups. A breadfruit-based rodent chow was formulated by substitution of all of the wheat in the standard formulation with breadfruit. The diets were isocaloric, nutrient equivalent and used to feed male and female C57BL/6 mice for 21 days. No sign of malnutrition, discomfort, illness or death was observed among the mice because of the diet. The histology and the cytokine expression of the mice ileum from both groups were analyzed and showed similar results. The expression of major bacteria was measured in the colon and showed similar results. Mice fed the breadfruit diet had a significantly higher growth rate and body weight than standard diet fed mice. No negative health outcomes were observed in studies with in vitro or in vivo models and breadfruit flour is a healthy alternative to other starches for modern foods.