With the possible exception of people suffering from advanced heart disease, whose doctors have ordered a low-fat diet for medical reasons like reversing atherosclerosis, the human body needs significant amounts of dietary fat to function properly — the main issue is what kind of fats, from what sources.
As researchers have noted, between the long-lived populations of the “Blue Zones” there is a wide range of fat intakes, from the 10-12% fat of Okinawan diets, to around 30% for some Mediterranean groups like Icaria, or Sardinia. What these long-lived peoples have in common is that the sources of fat are minimally processed, and from plants: nuts, seeds, avocados, or whole olives more than olive oil. Even when oil is used, it’s minimally processed, e,g. made directly from mechanical pressing without further chemical treatments.
The least healthy fat is saturated fat, where the balance of evidence continues to show strong associations with heart disease risk. But even there, the source of saturated fats matter: it’s animal or processed saturated fats that are strongly associated with worsening cholesterol (thus raising heart disease risk), and lipotoxicity (increasing type 2 diabetes risk), while also bringing unwanted toxins like pesticides, growth hormones, glycotoxins, etc. which are stored in animals’ fat cells. Whereas, plant fats in their whole form are generally clean, and loaded with supporting antioxidants, phytonutrients, and fiber. Even with the whole plant foods containing more saturated fat (e.g. whole coconut flakes), the fiber and other nutrients counteract the typical bad effects of saturated fats. But this kind of “package deal” of foods is not at all conveyed on current food label standards.