I disagree about the same origins in every case of Orthorexia Nervosa, as that can arise from wanting to avoid foods that cause inflammation, IBS and various autoimmune problems.
These problems are more common among young women than among any other age group, as they have the strongest immune systems.
F 5 ft 3. HW: 196 lbs. Primal SW (May 2011): 182 lbs (42% BF)... W June '12: 160 lbs (29% BF) (UK size 12, US size 8). GW: ~24% BF - have ditched the scales til I fit into a pair of UK size 10 bootcut jeans. Currently aligning towards 'The Perfect Health Diet' having swapped some fat for potatoes.