Fake-Fast diet may soothe gum treatment side effects

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Age 18-70 years * Periodontitis stages III-IV, generalized, grade C-B (according to the New World Workshop 2017) * Minimum of 20 teeth present: to ensure there are sufficient teeth for study and that the same teeth can be examined in all participants. * Systemically healthy participants (self-reported questionnaires will be used). * Body mass index: 18.5-30 kg/m2 (normal weight to overweight, but not obese) * Be willing and competent (verbally and cognitively) to give written informed consent and complete a medical history form * Be willing and physically able to carry out all study procedures (e.g. multiple cycles of a 5-day dietary regimen and blood samples) * Absence of hopeless teeth, acute dental conditions, teeth with endodontic-periodontal lesions and necrotising periodontal diseases Exclusion Criteria: * Age \> 70 years. Exclusion for safety and feasibility reasons and to minimize the complicating factors such as frailty and un-/under-diagnosed medical conditions. * Less than 20 teeth present * Patients who received any periodontal treatment in the last 12 months * Smoking (defined as self-reported use of any cigarettes or electronic cigarettes for at least 5 years): to avoid the potential confounding effect of smoking * Mental illness, including severe depression, dementia. To ensure safety and compliance of the protocol * Drug dependency * Hormone replacement therapy (DHEA, estrogen, thyroid, testosterone). * Severe hypertension (systolic BP \> 200 mm Hg and/or diastolic BP \> 105 mm Hg) * Underweight (BMI \< 18.5 kg/m2) * Currently taking part in other clinical trials: to prevent either from interfering with the results of the other * Pregnant or breastfeeding women: to prevent hormonal changes from influencing the amount of inflammation * Taking medications including systemic anti-inflammatory medication within 3 months of the study (NSAIDs, no more than once per week and not in the week before sample collection, is permitted) * Systemic antibiotic intake within 3 months: to prevent their microbiome-modulating effects from impacting the inflammatory status. * Current orthodontic treatment: interferes with plaque control measures. * Alcoholism (alcohol intake greater than two drinks per day for women and three drinks per day for men) * Denture wearer/presence of dental implants: They may have an effect on periodontal parameters of neighbouring teeth * Obvious signs of untreated caries and other significant oral diseases which in the opinion of the Study Dentist will affect either the scientific validity of the study, or if the volunteer was to participate in the study would affect their wellbeing * Unable or unwilling to participate in baseline or follow-up examinations * Unable or unwilling to complete the dietary intervention * Special dietary requirements incompatible with the study interventions * Significant food allergies which would make the subject unable to consume the food provided