Abstract In this paper, a quantitative reconstruction of Middle Neolithic diet in the area of Falbygden, Sweden, is attempted. The reconstruction is based on carbon and nitrogen isotope values for human bone collagen in the passage grave at Fralsegarden as well as on a series of animal and cereal isotope measurements from the same area and period. The Bayesian software package FRUITS is employed, resulting in estimates of the caloric contribution of plants, terrestrial animals, and fish to the diet. Two models were developed, one based on carbon and nitrogen isotope values in adult bone collagen and one based on carbon and nitrogen isotopes in tooth enamel and collagen. The estimates from both models are similar, suggesting a high caloric contribution from plants and a smaller one from terrestrial animals while the contribution from freshwater fish is marginal. These results contradict some earlier views regarding Neolithic economy on Falbygden and suggests that Funnel Beaker society in this region was heavily reliant on cultivation, rather than a pastoral economy with only marginal importance of cereals.