There is increasing interest from consumers in local food systems (LFS) in which consumers purchase their food from predominantly local sources. This paper investigates the claim that LFS use less energy and emit less greenhouse gasses than mainstream food systems (MFS), such as supermarkets. We calculated the energy required during part of the lifecycle of a selected number of food items sourced by different food supply systems and their resulting greenhouse gas emissions. Data were collected from literature, interviews with producers and suppliers of food, experts, and internet. Our results show that in the base simulation of full summer season and only inland, open-air production, energy uses and carbon dioxide emissions are slightly higher in LFS compared to the MFS, but in the same order of magnitude. LFS can be more sustainable by optimizing their transport and storage through minimizing the transport distance and by increasing the stored and traded quantities. Supermarkets could be more sustainable through choosing in-season food products that are homegrown in open air as well and by minimizing distances and storage times. Also consumers could have a large impact through a consistent choice for these in-season, inland products and through their shopping trips.