Diet significantly influences mental health and wellbeing, but this link is firmly established only in some areas such as the ability of a high fat and low carbohydrate diet (a ketogenic diet) to help children with epilepsy, and the effect of vitamin B12 deficiency on fatigue, poor memory, and depression, says a study. The research, published in the journal European Neuropsychopharmacology, cautions that the evidence of a ink between diet and mental health for many diets is comparatively weak.