The avocado is a fruit from a the Persea americana tree. Its knobbly, green tough outer skin has earnt it the alternative name of the alligator pear. Avocados are native to Central American regions where they have been cultivated for thousands of years, but have more recently been introduce to Asia, Australia and North America. There is a wide variety amongst avocado bearing trees with some preferring humid tropical regions (West Indian), some preferring cooler high altitude tropical regions (Guatemalan) and some preferring dry sub-tropical plateaus (Mexican). All varieties produce a hard fruit that ripens over time to produce a soft flesh with a buttery texture that surrounds a hard central nut. The buttery texture of the fruit is on a large part due to its high content of fat. The fat content of avocados is unusual for a fruit as fruits are generally not known for their fatty acids (olives being another exception). The presence of fatty acids and other nutrients makes the avocado unique and therefore interesting nutritionally.
Like all plant foods, the avocado is high in a large number of essential nutrients including potassium and a range of B vitamins. The potassium content of the avocado is particularly high with one avocado containing the same amount of potassium as two or three bananas (a fruit known for their high potassium content). In fact a 100 gram serving of avocado supplies between 400 and 500 grams of potassium. This makes the avocado a particularly good fruit for rebalancing the sodium to potassium ratio in those with excessive sodium intakes brought about by poor quality processed foods. As with most plant foods containing high concentrations of fatty acids, the avocado has a concomitantly high concentration of vitamin E to protect the fatty acids from lipid peroxidation and rancidity. The fatty acid content of the fruit is around 15 grams per 100 gram serving, with 10 grams of this being provided by monounsaturated fatty acids, 3 grams from polyunsaturated fatty acids and the rest from saturated fatty acids.
Avocados have been shown to have beneficial effects on blood sugar levels. This may relate to their high fibre and fat content, both components being known to slow the digestion of starch and absorption of glucose from the gut. However, avocados also contain the sugar D-mannoheptulose that is a known hexokinase inhibitor. Hexokinase is an enzyme required for the phosphorylation of glucose in the glycolytic pathway. By inhibiting glycolysis in the pancreas, ATP concentrations are kept low and this prevents the depolarisation of the membrane required for the influx of calcium, a step that is necessary for the release of insulin from the beta cells of the pancreas. Animal studies show that D-mannoheptulose is able to lower blood sugar levels in experimental models. The beneficial blood sugar effects of avocados may explain their ability to lower blood cholesterol levels, although this may also relate to their high content of antioxidant (including vitamin E) or their polyunsaturated fatty acid component.
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