To enhance and advance both human and planetary health, it is imperative to transition towards more sustainable nutrition approaches. This study aimed to assess the correlation between the levels of sustainability and sustainable nutrition knowledge, attitudes towards sustainable nutrition, and adherence to the Mediterranean diet (MD) among blue- and white-collar employees. This study included 210 adults, half of whom were white-collar employees, with the other half being blue-collar employees. Sociodemographic data were collected, and anthropometric measurements were performed. The Questionnaire on Food Sustainability Knowledge and Attitudes to Sustainable Eating and the Mediterranean Diet Adherence Scale (MEDAS) were also included in the applied survey. Dietary intake was assessed using 24 h dietary records. The mean age was 41.9 ± 10.87 years. Of the participants, 56.2% were classified as being overweight or obese. The level of knowledge on the concept of “food sustainability” among all participants was 30.5%. The mean MEDAS score of all the participants was 5.4 ± 1.90, and 74.8% of all the participants did not follow the MD. Positive correlations were found between the MEDAS score and the Sustainable Diet Definition score (r = 0.174) (p ˂ 0.05) and Sustainable Eating Attitude score (r = 0.312) (p ˂ 0.001). Negative correlations were found between the MEDAS score and body weight (r = −0.320; p ˂ 0.001), BMI (r = −0.249; p ˂ 0.001), waist circumference (r = −0.278; p ˂ 0.001), and PBF (r = −0.177; p ˂ 0.05). We found that, as the level of sustainable nutrition knowledge increased, sustainable nutrition behaviors improved, and as adherence to the MD increased, the incidence of obesity decreased.