Background In polymorbid patients with bronchopulmonary infection, malnutrition is an independent risk factor for mortality. There is a lack of interventional data investigating whether providing nutritional support during the hospital stay in patients at risk for malnutrition presenting with lower respiratory tract infection lowers mortality. Methods For this secondary analysis of a randomized clinical trial (EFFORT), we analyzed data of a subgroup of patients with confirmed lower respiratory tract infection from an initial cohort of 2028 patients. Patients at nutritional risk (Nutritional Risk Screening [NRS] score ≥3 points) were randomized to receive protocol-guided individualized nutritional support to reach protein and energy goals (intervention group) or standard hospital food (control group). The primary endpoint of this analysis was all-cause 30-day mortality. Results We included 378 of 2028 EFFORT patients (mean age 74.4 years, 24% with COPD) into this analysis. Compared to usual care hospital nutrition, individualized nutritional support to reach caloric and protein goals showed a similar beneficial effect of on the risk of mortality in the subgroup of respiratory tract infection patients as compared to the main EFFORT trial (odds ratio 0.47 [95%CI 0.17 to 1.27, p = 0.136] vs 0.65 [95%CI 0.47 to 0.91, p = 0.011]) with no evidence of a subgroup effect (p for interaction 0.859). Effects were also similar among different subgroups based on etiology and type of respiratory tract infection and for other secondary endpoints. Conclusion This subgroup analysis from a large nutrition support trial suggests that patients at nutritional risk as assessed by NRS 2002 presenting with bronchopulmonary infection to the hospital likely have a mortality benefit from individualized inhospital nutritional support. The small sample size and limited statistical power calls for larger nutritional studies focusing on this highly vulnerable patient population. Clinical trial registration Registered under ClinicalTrials.gov Identifier no. NCT02517476.