Avoid (cheap) vegetable oils such as sunflower and rapeseed oils and the derived products with hydrogenated oils, such as margarines.
Also, this health guide lists sunflower and "cheap" canola as examples of good unsaturated fats.
My favorite example is that a doctor once recommended that I follow the DASH diet to lower my blood pressure. The DASH diet was a modified version of the 1990s food pyramid. A relatively recent study compared it with diets that get fewer calories from carbohydrates, and while all the diets they tried did lower blood pressure, the original DASH diet was the worst of the bunch ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3236092/ ).