 Malnutrition is defined as a state of nutrition in which a deficiency, excess or imbalance of energy, protein, and other nutrients causes measurable adverse effects on body composition and function, and clinical outcome. In patients with mitochondrial disease there is by definition malnutrition on a cellular level due to disturbed metabolism with energy deficit. A logical next step is to study the effect of this energy shortage on complaints in the adult population by describing characteristics of this patient group in relation to the nutritional status. In the same vein, a controlled dietary intervention might result in an evidence based dietary therapy. 