AbstractAimThe aim was to assess two macronutrient interventions in a 2 × 2 factorial dietary design to determine their effects on oral health.Materials and MethodsParticipants (65–75 years old) with a body mass index between 20 and 35 kg/m² of a larger randomized control trial who consented to an oral health assessment were recruited. They had ad libitum access to one of four experimental diets (omnivorous higher fat or higher carbohydrate, semi‐vegetarian higher fat or higher carbohydrate) for 4 weeks. The periodontal examination included periodontal probing depth (PPD), clinical attachment level (CAL), and bleeding on probing. Oral plaque and gingival crevicular fluid (GCF) were collected before and after the intervention.ResultsBetween baseline and follow up, the number of sites with a CAL <5 mm (mean difference [MD] −5.11 ± 9.68, p = .039) increased and the GCF amount (MD −23.42 ± 39.42 Periotron Units [PU], p = .050) decreased for the semi‐vegetarian high‐fat diet. For the mean proportion of sites with PPD reduction of >1 mm and CAL gain of >1 mm, significant differences were calculated between the diets investigated. The clinical parameters were not associated with changes in the oral microbiota.ConclusionsThe results of this study provided evidence that a semi‐vegetarian high‐fat diet provides benefits to clinical parameters of periodontal health.This study is registered in ClinicalTrials.gov (ACTRN12616001606471).