Actually, for up to date research, you can subscribe to
www.vitasearch.com and receive weekly research abstracts. These are mainly nutrient-related studies versus diet-related, but if it's reference material you're looking for, this is an excellent source. The British Medical Journal (
www.bmj.com) is also good, as it
www.altmedreview. These are all no-cost options.
As a print magazine, I like the Townsend Letter, but it's alternative medicine, which includes but is not restricted to, nutrition.