Background Dietary protein sources and protein adequacy are crucial modulators of muscle quality and body composition. We investigated the association between dietary protein sources (and their adequacy) and prevalence of sarcopenic obesity (SO) in South Korean populations according to weight status. Methods The participants (n = 1,967) were classified into SO, obese, sarcopenia, and normal groups. A cross-sectional survey was conducted using the KS-15 questionnaire, short-form Food Frequency Questionnaire, and anthropometric measurements. Results Percentage of body fat (male: 28.43 ± 0.61%; female: 39.95 ± 0.36%) was significantly high, while appendicular skeletal muscle (ASM; male: 40.30 ± 0.36%, female: 32.47 ± 0.20%) was low in the SO and OB groups. Beef and pork consumption was negatively associated with ASM (%) but positively associated with body fat (kg and %) in the normal group. Among the people with excessive protein intake, the lowest quintile (Q1: 5.7 g/day) of beans and tofu consumption showed a 2.4-fold increase in the risk of developing SO (adjusted odds ratio: 2.41, confidence interval: 1.07–7.80), when compared with the highest quintile (Q5: 60.1 g/day). Similarly, with beans and tofu consumption, there was a 2.5-fold higher risk of developing sarcopenia in participants who had