the study will be conducted following different periods:~Free diet (for 4 weeks). After recruitment, the patient will enter free diet phase in which he/she will be asked to follow a normal free diet for 4 weeks. During this period, a nutritional interview will be carried out by a trained dietician who will elaborate a personalized diet and order the ketogenic products on the basis of patient's preferences.~very low calories ketogenic diet (for 8 weeks). After the free diet period, the patient will start the very low calories ketogenic regimen. At the beginning of this period a box with the commercial products necessary to cover the whole study period will be hand-delivered by a dietician that will instruct the patient on the correct use and storage.~Maintenance (for 12 weeks). After very low calories ketogenic diet phase, the patient will start maintenance period as described
Adult patients with fibromyalgia or symptomatic knee osteoarthritis and comorbid obesity eligible to a very low calories ketogenic diet will be enrolled in the pilot study