วันอังคาร, ธันวาคม 9, 2008

Potatoes, nutrition and diet

The potato is a good source of dietary energy and some micronutrients. But balanced diets need to include other vegetables and whole grain foods
Potato is a versatile, carbohydrate-rich food highly popular worldwide and prepared and served in a variety of ways. Freshly harvested, it contains about 80 percent water and 20 percent dry matter. About 60 to 80 percent of the dry matter is starch. On a dry weight basis, the protein content of potato is similar to that of cereals and is very high in comparison with other roots and tubers.

In addition, the potato is low in fat. Potatoes are rich in several micronutrients, especially vitamin C - eaten with its skin, a single mediumsized potato of 150 g provides nearly half the daily adult requirement (100 mg). The potato is a moderate source of iron, and its high vitamin C content promotes iron absorption. It is a good source of vitamins B1, B3 and B6 and minerals such as potassium, phosphorus and magnesium, and contains folate, pantothenic acid and riboflavin. Potatoes also contain dietary antioxidants, which may play a part in preventing diseases related to ageing, and dietary fibre, which benefits health.

Key points
The potato is a good source of dietary energy and some micronutrients, and its protein content is very high in comparison with other roots and tubers.

Potato is low in fat - but preparing and serving potatoes with high fat ingredients raises the caloric value of the dish.

Boiling potatoes in their skins prevents loss of nutrients.
Potatoes are important in many diets, but need to be balanced with other vegetables and whole grain foods.

Further research is needed to determine the link between potato consumption and Type 2 diabetes.

Effects of potato preparation methods

The nutritive value of a meal containing potato depends on other components served with them and on the method of preparation. By itself, potato is not fattening (and the feeling of satiety that comes from eating potato can actually help people to control their weight). However, preparing and serving potatoes with high-fat ingredients raises the caloric value of the dish.

Since the starch in raw potato cannot be digested by humans, they are prepared for consumption by boiling (with or without the skin), baking or frying. Each preparation method affects potato composition in a different way, but all reduce fibre and protein content, due to leaching into cooking water and oil, destruction by heat treatment or chemical changes such as oxidation.

Boiling - the most common method of potato preparation worldwide - causes a significant loss of vitamin C, especially in peeled potatoes. For french fries and chips, frying for a short time in hot oil (140ºC to 180ºC) results in high absorption of fat and significantly reduces mineral and ascorbic acid content. In general, baking causes slightly higher losses of vitamin C than boiling, due to the higher oven temperatures, but losses of other vitamins and minerals during baking are lower.

Nutrient content of potatoes

(Per 100 g, after boiling in skin and peeling before consumption) Source: United States Department of Agriculture, National Nutrient Database

Toxic components of potato

As part of the potato plant's natural defences against fungi and insects, its leaves, stems and sprouts contain high levels of toxic compounds called glycoalkaloids (usually solanine and chaconine). Glycoalkaloids are normally found at low levels in the tuber, and occur in the greatest concentrations just beneath the skin. Potatoes should be stored in a dark, cool place in order to keep glycoalkaloid content low. Under exposure to light, potatoes turn green in colour due to increased levels of chlorophyll, which can also indicate higher levels of solanine and chaconine. Since glycoalkaloids are not destroyed by cooking, cutting away green areas and peeling potatoes before cooking ensures healthy eating.

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