BackgroundMetabolic syndrome (MetS) has become a growing risk factor of some non-communicable diseases. Increase of greenhouse gas emissions affects the planet.AimsTo assess the association between MetS severity and amount of carbon dioxide (CO2) emitted in an adult population.DesignCross-sectional study (n= 6646; 55-76-year-old-men; 60-75-year-old-women with MetS).MethodsDietary habits were assessed using a pre-validated semi quantitative 143-item food frequency questionnaire. The amount of CO2emitted due to the production of food consumed by person and day was calculated using a European database, and the severity of the MetS was calculated with the MetS Severity Score.ResultsHigher glycaemia levels were found in people with higher CO2emissions. The risk of having high severe MetS was related to high CO2emissions.ConclusionsLow CO2emissions diet would help to reduce MetS severity. Advantages for both health and the environment were found following a more sustainable diet.Trial registrationISRCTN,ISRCTN89898870. Registered 05 September 2013.