The purpose of this secondary analysis was to examine the relationship between protein and essential amino acids (EAAs) intake with the level of muscle mass (MM) independent of the diet. Twenty-one omnivores, 22 ovo-lacto-vegetarians and 20 vegans were recruited. MM (urinary creatinine), dietary intake (5-day dietary records) and biochemical analyses (urinary and plasma sex hormones) were obtained. We observed no significant difference between groups for MM, total EAA intake, leucine, isoleucine, age and body mass index. However, we observed a significant difference between groups for total dietary protein intake and total energy intake. Despite significant differences in total dietary protein, the EAA intake was not different, indicating that neither the amount nor the quality of protein in these diets was a limiting factor in determining the amount of MM. Thus, each of these diet patterns appears adequate to maintain MM.