ObjectiveThe prevalence of obesity by fat percentage has seen a steady increase in older adults in recent years, secondary to increases in fat mass in body composition, even in healthy aging. Malnutrition is a common geriatric syndrome with serious clinical outcomes. Increases in fat mass and waist circumference with healthy aging should not prevent the risk of malnutrition from being masked. Malnutrition is often ignored in obese older people due to low BMI cut-off values in many screening tests. The present study seeks to raise awareness of the need to assess the frequency of undernutrition and related factors in obese older adults.MethodsThe data of 2013 community-dwelling patients aged ≥ 60 years who applied to a university geriatrics outpatient clinic between April 2012 and November 2022 were analyzed retrospectively, of which 296 were found to be obese based on fat percentage and were included in the study. Demographic data and the presence of any geriatric syndromes were obtained retrospectively from the patient files, functional status was assessed using the KATZ Activities of Daily Living (ADL) Scale and the LAWTON-BRODY Instrumental Activities of Daily Living Scale (IADL); frailty was screened using FRAIL-scale; and the sample was assessed for malnutrition using the Mini Nutritional Assessment-Short Form (MNA-SF), with undernutrition defined as an MNA-SF score of ≤11.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\le 11.$$\\end{document} The patients’ fat percentage and weight were measured using a bioimpedance analyzer. Fatty obesity was defined using the Zoico methodology (fat percentage ≥\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\ge$$\\end{document} 27.3% for males, ≥\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\ge$$\\end{document} 40.7% for females),\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$,$$\\end{document} handgrip strength (HGS) was measured using a hand dynamometer, and probable sarcopenia was defined as low HGS based on regional cut-off values (35 kg for males, 20 kg for females).ResultsThe mean age of the 296 fatty obese older adults (102 males/194 females) was 74.4 + 6.5 years, and the median fat was 42.2% (27.4–59.5). Undernutrition was detected in 19.6% of the patients based on MNA-SF screening. A univariate analysis revealed age, sex, educational status, daily physical activity status, depression, difficulty in swallowing, chewing difficulty, probable sarcopenia, number of chronic diseases, and IADL to be associated with undernutrition, while a multivariate logistic regression analysis revealed depression [OR = 3.662, 95% CI (1.448–9.013), p = 0.005] and daily physical activity status [OR:0.601, 95% CI (0.417–0.867), p = 0.006] to be independently associated with malnutrition in obese older adults based on fat percentage.Conclusion The present study clarifies the significance of undernutrition in obese older adults also in our country, and recommends undernutrition screening to be carried out, by fat percentage, on obese older adults, especially with depression and low daily physical activity.