Avocadoes are a famously fatty fruit. Originating in South America and cultivated for millennia in Mexico, the green-fleshed avocado was once believed to be a dieter's nightmare, containing more fat and calories per pound than almost any other natural food [source: Gibson].
But recent scientific research has discovered that avocadoes are actually loaded with "good" monounsaturated and polyunsaturated fats. These types of fat, while still relatively high in calories, actually help lower cholesterol levels and decrease the risk of heart disease, which is the leading cause of death for Americans [source: CDC].
There are six commercial varieties of avocadoes in the United States, but Hass is by far the dominant breed. California grows 90 percent of the avocadoes sold in America, and 95 percent of those avocadoes are of the Hass variety [source: California Avocado Commission]. You can distinguish the Hass avocado by its oval shape, slightly bumpy skin and nifty ability to darken from green to black as it ripens. Inside, the seed or pit of the Hass is medium-sized, compared to the seeds of other varieties.
The trick to buying avocadoes is determining the ripeness of the fruit. The skin of a ripe, ready-to-eat avocado will give a little when pressed firmly. If it's hard, the avocado isn't ready. If your thumb practically breaks through the skin, it's overripe. To ripen a green avocado, place it in a paper bag and keep it on the kitchen counter for a few days. To speed up the process, toss in a ripe banana or apple. These fruits give off ethylene gas, a natural ripening agent [source: California Avocado Commission]. When the avocado skin has taken on a uniform dark color, give it a squeeze.
Avocadoes stuff a tremendous amount of nutrients into a small package. They're loaded with dietary fiber, vitamin B6, vitamin C, vitamin E, potassium (60 percent more than bananas), magnesium and folate, and they contain absolutely no cholesterol or sodium [source: CDC].
The fat content of avocadoes is truly impressive. A medium-sized avocado contains 30 grams of fat -- as much as a quarter pound of beef [source: WebMD]. But as we mentioned before, this is mostly "good" fat. Of the 4.5 grams of fat in each serving of avocado (7 percent of the daily allowance), 3.5 grams are monounsaturated and polyunsaturated fats.
These unsaturated fats raise the body's levels of high-density lipoprotein (HDL) -- also known as "good" cholesterol -- and lower levels of low-density lipoprotein, the "bad" cholesterol that contributes to heart disease. For that reason, the American Heart Association recommends a diet that contains 30 percent of calories from healthy unsaturated fats like avocado [source: California Avocado Commission].
Avocadoes pack a lot of calories, but are far lighter than other processed alternatives like butter or mayonnaise [source: WebMD]. As we mentioned before, two tablespoons of avocado carries 4.5 grams of fat and 50 calories. The same amount of butter has 23 grams of fat (16 of them saturated fats), 204 calories and high levels of cholesterol and sodium.
When eaten in moderation, avocadoes can provide healthy fats for a balanced diet and contribute to long-term cardiovascular health. Keep reading for lots more information on a heart-healthy diet.