Avocados seem almost too luscious to be healthy, but the fat they contain (and there's quite a bit) is highly monounsaturated, the kind that's associated with a healthy heart. Avocados are also rich in vitamin E, another heart helper. Although the banana is thought of as an exemplary potassium source, the avocado actually supplies 60% more potassium gram for gram. These velvety "vegetable fruits" are high in fibre, and provide substantial amounts of folate (folic acid), vitamin B6, and pantothenic acid, as well as some iron, copper, and magnesium.

On the phytochemical front, avocados contain glutathione, an antioxidant with anticarcinogenic potential. They also contain a significant amount of a choelsterol-lowering phytosterol called beta-sitosterol.

Buying
Select heavy, unblemished avocados. Many markets sell avocados that are hard and unripe, because they're less likely to bruise and spoil. If the avocado is rock hard, it will need a few days to ripen. If an avocado yields slightly to gentle pressure, it is ripe enough to slice. If pressing the fruit leaves a small dent, it is too ripe to slice, but is suitable for mashing. If pressing leaves a large dent, the fruit is overripe, and the flesh will have darkened and spoiled.

Storage
Hard avocados ripen at room temperature in three to six days. To speed up the process, place them in a paper bag, preferably with a tomato. Never put hard avocados in the refrigerator because they will never ripen. Keep ripe avocados in the refrigerator and use within two to three days.

Preparation
To pit an avocado, cut it lengthwise all the way around (working around the pit) and gently twist the two halves apart. Tap the blade of a heavy knife into the pit, and twist gently to release the pit from the flesh. To skin and slice the fruit, place the halves face down and peel off the skin. (If the flesh is very soft, scoop it out of the skin with a spoon instead.) If the skin is too tough to peel easily, use a paring knife to score it into peelable strips. Cut the flesh into thin slices, or chop into chunks.

The flesh of cut avocado turns dark within a few minutes when exposed to air. This doesn't affect nutrition or flavour, but makes the avocado look less appetising. To delay darkening, rub slices with lemon or lime juice, and add the juice to mashed avocado when making guacamole or similar dips. Pressing plastic wrap firmly over the cut surface of a halved avocado, or onto the surface of a bowl of mashed avocado, will deter darkening.