FutureLearn.com, Coursera.org and Open2Study.com offer free nutrition classes, as of 2015. A comprehensive listing of massive open online class offerings, or MOOCs, is available on Mooc-List.com.
An example of a free online nutrition class is "The Science of Nutrition" course offered on FutureLearn.com. The class is four weeks long and requires three hours per week. This course covers multiple aspects of nutrition including its biology, chemistry and physics, among other related topics.
The class offered on Coursera.org, "Nutrition, Health, and Lifestyle: Issues and Insights," is a seven- week course that delves into core nutrition concepts, dietary patterns and nutrition in the media.