Abstract: The Mediterranean diet is recognized as one of the healthiest diets worldwide and is associated with the prevention of cardiovascular and metabolic diseases, among others. Dietary habits are considered one of the strongest modulators of the gut microbiota, which seems to play a significant role in the health and disease of the host. The purpose of the present study was to evaluate interactive associations between gut microbiota composition and habitual dietary intake of 359 adults (normal weight, overweight and obese subjects). Dietary intake and adherence to the Mediterranean Diet tests together with fecal samples were collected from each subject. Fecal 16S rRNA sequencing was performed and checked against the dietary habits. MetagenomeSeq was the statistical analysis applied to analyse at species taxonomic level. Results from this study confirm that a strong adherence to the MD increases the population of some beneficial bacteria improving microbiota status towards a healthier pattern. Bifidobacterium animalis is the species with the strongest association with the MD. One of the highlights is the beneficial role of SCFA production, specially butyrate. This study shows that MD, fibre, legumes, vegetables, fruit and nuts intake increase butyrate-producing taxa such as: Ruminococcus faecis, R. bromii, Oscillospira (Flavonifractor) plautii and Butyricicoccus pullicaecorum. Further research is needed to understand how specific bacterial growth can affect the microbiota. Does growth of a beneficial bacteria always mean health?