The National Post reports in its Thursday edition that NDP leadership candidate Avi Lewis plans to lower grocery bills nationwide with a national "public option" to compete with major supermarket chains, but economists warn it may be challenging. The Post's Rahim Mohamed writes that University of Guelph food professor Mike Von Massow says: "I think it would be profoundly expensive, and very difficult to make succeed, for a relatively marginal benefit for Canadians. If you wanted to provide food support for low-income or underserved Canadians, there are much more cost-effective ways of doing that." Mr. Lewis says the federal government has the capacity to buy food directly from distributors and then sell it to Canadians at cost via non-profit grocery stores. Mr. Lewis called his plan for public grocery stores a "fantastically popular policy that I think (the NDP) can win with." Five large chains, three domestic and two foreign, control about three-quarters of the Canadian market for groceries. Mr. Von Massow said that, even if government-owned grocery stores integrated seamlessly into the market, they would still offer a relatively small savings for the average customer, given already thin profit margins for grocers.