The Skinny on the Fat and Calories. Avocados are high in fat. But it's monounsaturated fat, which is a good fat that helps lower bad cholesterol, as long as you eat them in moderation. Avocados have a lot of calories. The recommended serving size is smaller than you’d expect: 1/5 of a medium avocado (or 1 ounce) is 50 calories. Store avocados at room temperature, keeping in mind that they can take 4 to 5 days to ripen. To speed up the ripening process, put them in a paper bag along with an apple or banana.