There is more and more research pointing to an inflammatory causation of depression and anxiety.
Naturopathic Doctors can use a combination of diet, supplements and herbs, to combat depression, anxiety or other related symptoms using a holistic approach that is not entirely based on the biochemical model. This here is an excerpt from a ND in the United States speaking on the use of herbal medicine to treat insomnia, with the idea that immune-cytokine dis-regulation may be at the basis for the ability to sleep sound.
The aim of our practice is to identify the cause of the symptom(s), and thereby improve the function of the body’s different systems so as they function better as a whole. We can see the gut-immune-neurological connection here, where dysfunction in the digestive system can lead to inflammation. Since a large part of the immune system is found just under the brush border of the intestines, there you can see the hyper-stimulation of the immune system that sends different signalling molecules (cytokines) to increase inflammatory response and to respond to the injury of the digestive tract. How this affects the nervous system is yet to be elucidated, however my theory is the role of stress on the neurological system, both at the sensory and perceptive level.