As mentioned above the conversion of food energy into ATP is a crucial function of mitochondria. You might think that because affected mitochondria are less efficient at making ATP that you could overcome this by eating more.
Unfortunately this is not the case and all that this achieves is that you get heavier. Nor does it seem that one type of food is easier to convert into ATP than another, and so high carbohydrate or high fat diets are not of benefit. Food contains vitamins and minerals as well as energy and it has been suggested that increasing the amount of certain vitamins may help. Many patients are prescribed ubiquinone, a vitamin that works in the mitochondria. No one is certain that this is of benefit, but there is no doubt that some patients feel better taking ubiquinone. However, others feel no benefit. In the clinic we usually suggest people try it for a period of 3 months to see if it helps. Some younger patients are also given riboflavine and thiamine vitamins. There is even less evidence that these help, but again they are unlikely to do harm and do help some patients.
During minor illnesses it is important to avoid fasting and dehydration. Many patients benefit from having small snacks or high calorie drinks at hand to consume during vigorous activity.
Overall, the best advice is to eat as balanced a diet as possible, and that it may be worth trying ubiquinone or other vitamins on the advice of the specialist.