Any balanced diet should provide a fat intake that will be adequate for an endurance athlete. That being said, it’s good to point out that a balanced diet, as described before, should include a mix of fruits, vegetables, fish and meat, legumes, nuts, maybe some dairy and whole grains. The fish, meat and nuts in the diet will probably be the main contributors to dietary fat, as well as some dairy if included in the diet. As long as an athlete consumes 20-40% of their calories in the form of fat, and not too much being contributed by added fats and oils in processed foods, the balance of fats present in the diet should probably be fine from a health standpoint. Ideally, it will be better to get meats in a free-range, grass fed form rather than a grain fed, caged, antibiotic/hormone derived form (which have a less-healthy distribution of fat-types).
For a long time, it’s been clear that artificially saturated “trans fats” are not good for health, but it’s also becoming increasingly common for people to not be concerned about consuming saturated fats derived in their natural forms from animal sources (like meat and dairy), but rather, people are increasingly concerned about added fats like cheap vegetable oils added to processed foods (like corn or soybean oil), because of the specific mix of fatty acids. Specifically, there is concern about consuming high amounts of omega-6 fatty acids relative to much lower amounts of omega-3 fatty acids. There may be other specific problem areas identified by current research, but that seems to be the most prominent lately. (As an aside, it still seems that olive oil, avocado oil, coconut oil, and maybe macadamia oil are preferred fats for cooking or adding to recipes if you’re preparing food. Clearly, these aren’t commonly used by the food industry, because corn oil, soybean oil, and sometimes canola oil are cheaper and/or taste better for whatever product they might be making.)
Generally, beyond simply taking in a balanced diet like that being advocated, it could be good to focus on seeking out good sources of healthy fats and/or better choices that offer better fat profiles. For example, choosing salmon instead of poultry as a source of protein, choosing almond butter over peanut butter, limiting or eliminating processed foods that have added sugars and oils, or maybe even supplementing with fish oil. The basic idea being that some fat sources are higher in Omega-3 fatty acids, monounsaturated fats, or shorter chained fatty acids that are either better for your health, reduce inflammation, or burn more efficiently as fuel.
I’ll admit that I don’t know enough about the various specific forms of fatty acids that are out there and their affects, positive and negative on the body, whether health or performance related. Not because I haven’t read a lot about them, but because there seems to be an ever expanding knowledge base on the subject. Each new study about various types of fats, their intake, the proportions of their intake, etc. all seem to indicate the need for a more nuanced understanding of what could be considered an optimal diet with regards to fats. And, as with most things of a complex nature, there are studies that seem to provide conflicting conclusions when examining individual components of the diet, so it may be best to take a relaxed, but informed approach that focuses on balanced, healthy meals, rather than worrying too much about esoteric details.
That being said, it’s good to be aware of the general truths that hydrogenated “trans” fats are not good for you. Saturated fats may be questionable, but it also depends on how long the fatty acid chains are, with short and medium chain fatty acids being very good fuel sources that require less oxygen to burn than longer fatty acids. Namely, coconut oil has become a popular subject, because of its very high concentration of medium chain fatty acids. Likewise, dairy fat has a large portion of its fatty acids in this form. And again, limiting fats that come from grain fed, caged animals, and seeking out omega-3 fatty acids and monounsaturated fats should do you good in the long run.
Ultimately, it seems clear that salmon and other cold-water fish, grass-fed, free-range meat products, most nuts and flaxseeds, olive oil, macadamia oil, avocado and avocado oil, and even fish oil supplements should be good sources of healthy fats, hopefully making up the majority of the fat consumed.