We know some foods have a negative impact on your gut health. For example:
Factory-farmed meat [Source: PubMed]
Fizzy drinks [Source: PubMed]
Saturated fats [Source: PubMed]
While the study on saturated fats and gut health used mice, not human, it suggests that saturated fats might not be as good for your gut as poly-unsaturated fats such as oily fish, avocados, nuts and seeds. [Source: NIH].