Considering the way fat has been demonized you would be unusual if you didn’t have concerns. Most of us here have been through this and have come to the realization that the concerns are largely unfounded at least for ourselves.
But there are potential pitfalls of a high fat diet.
One is it can increase the loss through urine of electrolytes and in particular sodium similar to what occurs when one fasts. This leads many to experience flu like symptoms after going high fat though it can be addressed by upping intake of electrolytes and going “high salt”. Another big sin according to conventional wisdom…
Another issue is that people eating a typical western diet tend to eat a poor mix of fats. Lots of refined vegetable oils with an excessive balance of omega 6’s compared to omega 3’s. The refining process strips them of their natural anti-oxidants such as vitamin E making these unstable highly unsaturated oils highly prone to oxidative damage, aggravated by using these oils for high heat cooking and frying.
Many people eating keto eat a lot of fried bacon and other fried and charred meats and fats. I think this is a sub-optimal choice with some potential to aggravate problems for those with diabetes and other metabolic health issues. But more highly saturated animal fats are less damaged by this than the vegetable oils that have been promoted as healthy solely on the basis of a slightly lower cholesterol response.
Elevated ldl is another frequent issue for those going keto. But in general hdl goes up more and triglycerides fall dramatically. The change in hdl and triglycerides correlates strongly with ldl changing to a much more healthy pattern even when ldl rises too. Unfortunately standard medical practice relies on very basic and inadequate lipid tests which fail to identify the sub-types of ldl and their particle counts. Markers of inflammation such as CRP which tend to fall on a keto diet are also correlated with a reduced risk of atherosclerosis which is the primary threat of elevated ldl.
Fat metabolism and carbohydrate metabolism each involve some unique genes. Mutations in any of those genes may lead to impairment of fat or carbohydrate metabolism. If you have diabetes it is an impairment of carbohydrate metabolism. If you have a genetic predisposition to impaired fat metabolism than going high fat has the potential to make things worse, but the odds of this appear slim. Treading carefully and watching for trouble should reduce the risk further.