What are you buying? It helps to buy fruit and veg that are in season as they are usually cheaper. Also shop around, and look out for the special offers and promotions. Depending on what plan you're on meals can be bulked out with cheaper ingredients so that they go further.
Personally I find I spend less because now I'm planning my menus and I only buy what I know I need and will use. No impulse buys, no junk foods, and no food going to waste in the fridge that ends up getting thrown out. Also I take lunch to work whereas before I would have nipped out to the shop or cafe to get something, so saving money there too.