There are many nutritionally related causes of stress, anxiety or low mood, the most common being sub-optimal nutrition resulting in poor mental and physical energy. A disturbed blood sugar balance can result in periods of decreased mood. People who produce excessive amounts of histamines are also more likely to suffer. Adrenal exhaustion, usually brought on by stress and the over use of stimulants can have this effect. If you are constantly stressed or anxious and experiencing this 'fight or flight' response, your body will become increasingly incapable of dealing with these effects and your symptoms will worsen.