Background The high incidence of diverticulitis and hemorrhoidal proctitis episodes in the population imposes an important healthcare and economic burden. Aim To determine the association between intake of certain plant foods and diverticulitis and hemorrhoidal proctitis episodes. Methods Case-control study with quantitative food frequency questionnaire focusing on selected plant foods and derived products. These were grouped by main chemical components into: ethanol, caffeine/theine/theobromine, capsaicin, alliin, acids, eugenol, and miscellaneous foods like curcumin. We quantified intake according to 24-h recall, either on a 1-4 scale (no intake, low, moderate, high intake) or as the number of units consumed (e.g. cups of tea/coffee, n of oranges or lemons); this value was multiplied by the number of reported intake days per week (1-7). Overall intake was expressed as a continuous variable obtained by successively multiplying the score for each food category, and the result was transformed into a common logarithm (range 0.3 to 27.7). Cases and controls were compared using the chi-squared test, student’s t test, odds ratio (OR) and 95% confidence interval (CI), and predictive analysis (multiple logistic regression). Results The sample included 410 cases and 401 controls, who were similar in mean age and gender distribution. The mean score for overall intake of included plant foods was 6.3 points (standard deviation [SD] 4.5), and this was significantly higher in cases (8.5 points, SD 5.3) than in controls (4.1 points, SD 1.2; p < 0.001). Overall intake was similar in cases presenting diverticulitis or hemorrhoidal proctitis. Cases had 13 times the odds of being in the upper quartile for overall intake (> 7 points) compared to controls (OR 13.2, 95% CI 8.3 to 20.8, p < 0.001). Predictive logistic regression models showed that the chemical food group most closely associated with diverticulitis and hemorrhoidal proctitis was capsaicin, followed by ethanol, eugenol, caffeine/theine/theobromine, and acids. The OR for age was near the null value. Neither alliin nor miscellaneous food groups showed any association. Conclusions High, frequent consumption of some plant foods and derived products increases the risk of presenting symptoms of diverticulitis and hemorrhoidal proctitis.