The role of nutrition in onset, progression and treatment of periodontitis has not been thoroughly evaluated. In the present prospective clinical study, we investigated the influence of a nutritional intervention on changes in clinical, microbiological and immunological periodontal variables during a period of 12 months in patients with the metabolic syndrome and chronic periodontitis. Twenty female subjects with the metabolic syndrome and mild to moderate chronic periodontitis participated in a guided nutritional intervention programme. Examinations were assessed before, and at 2 weeks, 3, 6 and 12 months after intervention. Clinical measurements included probing depth, Löe and Silness gingival index and Quigley–Hein plaque index. In gingival crevicular fluid, periodontopathogens, levels of IL-1β and IL-6 as well as the activity of granulocyte elastase were determined. In stimulated saliva, antioxidative and oxidative variables were measured. After 12 months the following significant changes could be observed: reduction of clinical probing depth (2·40 v. 2·20 mm; P < 0·001), reduction of gingival inflammation (gingival index 1·13 v. 0·9; P < 0·001), reduced concentrations of IL-1β (4·63 v. 1·10 pg/ml per site; P < 0·001) as well as IL-6 (1·85 v. 0·34 pg/ml per site; P = 0·022) in gingival crevicular fluid. Bacterial counts in gingival crevicular fluid as well as oxidative and antioxidative variables in saliva showed no significant changes. Only salivary catalase showed a tendency to lower values. These findings indicate that in patients with the metabolic syndrome wholesome nutrition might reduce inflammatory variables of periodontal disease and promote periodontal health.