Background: Despite clinical interventional studies on the influence of diet on periodontal inflammatory parameters, there has been no practice-based cross-sectional study from a German population to date that has conducted both a comprehensive dental and periodontal examination and a thorough validated assessment of dietary behavior. Therefore, the aim of this pilot study was to evaluate, in a proof of concept, whether there is a correlation between the overall periodontal inflammatory surface area (PISA), periodontal clinical parameters (pocket probing depths (PPD), clinical attachment loss (CAL), bleeding on probing (BOP), furcation involvement (FI), tooth mobility (TM)), and the dietary behavior of patients with periodontal disease when utilizing a practice-based research network. The primary outcome was the correlation between the periodontal inflammatory surface (PISA) and the dietary assessment data. Materials and Methods: The practice-based research network, consisting of eight Master’s graduates, recruited patients who met the inclusion and exclusion criteria and performed a periodontal examination together with the assessment of dietary behavior using a digital version of the validated retrospective dietary recall (DEGS/RKI). Statistical analyses included linear regression models adjusted for age and smoking and unpaired t-tests, conducted using STATA 17.0 with a significance level of 5%. In addition, the data obtained were classified according to the currently recommended amounts of daily intake. Results: A total of 1283 teeth were analyzed, with 60.25% (773 teeth) requiring treatment. The average PISA was 753.16 mm² (SD ± 535.75 mm). Based on dietary guidelines, the studied population consumed excessive amounts of extrinsic sugars and fats, while their fiber and legume intake was insufficient. The intake of certain nutrients, including water-soluble fibers, specific fatty acids, vitamins (D, B1, B2, B6, and B12), iron, and zinc, was associated with reduced PISA, PPD, CAL, and BOP. Conclusion: Within the limits of the current study, including its cross-sectional design and cohort size, the outcomes demonstrated the influence of nutrition on periodontal health.