Is it possible to prime MDF with a more sustainable product to allow one to paint with a low VOC latex paint?

If you haven't installed it yet, you can get a very low VOC cold-pressed melamine coating applied to the MDF by Eco-Lumber Co-op. Unfortunately, if the MDF has been installed, there is not much you can do. It is true that it will swell if you use a latex paint on it. You will need to use a sealer. See the buildsmart directory (http://www.gvrd.bc.ca/buildsmart/Apps/searchResult.aspx?type=169&typeText=sealants) for low VOC alternatives. You could also try contacting Eco-Lumber Co-op for other options.