Alzheimer's disease, too much of any fat may make the term "healthy fat" a contradiction.
Besides, even within the mono- and poly-unsaturated fats, which consist mainly of vegetable foods, major differences in their nutritional profiles exist and not all of these foods should be accorded equal preference in the diet.
Take olive oil. A so-called staple of the Mediterranean diet, which has been associated with health benefits. But are Mediterraneans healthier because of or despite their widely publicized love affair with this empty calorie, which is what olive oil really is? Consider: two tablespoons contain 240 calories, all of it from fat (27 g), and most of it in the form of monounsaturated and polyunsaturated fats. Olive oil even provides a little vitamin E. But divorced as it is from its whole food source (olives), it provides no additional nutrition, and is devoid of fiber.
Now take an avocado. One large California avocado (black skin) provides 275 calories, and 25 grams of fat, most of it of the monounsaturated and polyunsaturated varieties, in addition to about 20% of the RDA for vitamin E, making it comparable to the above serving of olive oil. But what olive oil lacks, and avocado has, in sum cases in abundance, are the following essential nutrients: vitamin A, thiamin, niacin, vitamin B6, phosphorus, vitamin C, iron, riboflavin, manganese, copper, magnesium, potassium and zinc. One avocado also provides nearly 12 grams of fiber, half the RDA for women. It is truly packed with nutrition. And one beefy avocado dwarfs 2 measly tbsp. of olive oil, so you get more for your mouthful.
To sum up: When choosing dietary fats, opt for whole-food, plant-based varieties, which offer a plentitude of vitamins, minerals, water and fiber in addition to the hefty source of lipids they provide.