People affected by pathologies may not do the fasting mimicking diet, unless they have the prior approval of their specialized doctor. In the case of serious or relatively serious illnesses (cancer, diabetes, or cardiovascular, autoimmune, or neurodegenerative diseases), it is important to seek permission and approval from a disease specialist as well as from a dietitian with expertise in the fasting mimicking diet or in therapeutic fasting. The use of the fasting mimicking diet for disease treatment should for the moment be limited to clinical trials unless the doctor determines that there are no viable options and the patient cannot wait until the conclusion of appropriate clinical trials and FDA (US Food and Drug Administration), and similar agencies in other countries, approval.