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Starch

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Starch: What You Need To Know

 

 

Starch is a complex carbohydrate providing energy for the body. As an energy source, starch is often perceived by the public and the media as a fat contributor. It should be noted though, that starch is only stored as fat when a person consumes more than their daily requirements of energy.

Carbohydrates provide the body with energy, which it used for movement, breathing, and all internal metabolic functions. People’s main source of carbohydrates is starch, which is a bundle of many molecules of sugar that must be released from  by digestive enzymes before the body can process them. Sugar taken in excess of energy requirements is converted to fat and deposited under the skin and elsewhere (Jacoby and Youngson, 2005).

 

Starch in the diet

 

People tend to eat a large amount of starch in their diets because foods rich in starch are usually cheaper and more readily available than proteins. Starch provides a steady supply of glucose that the body requires for its metabolism to work.

Many weight-loss diets stress the importance of cutting down starchy foods. However, a person who does enough aerobic exercise on a regular basis has little to fear from gaining weight by consuming starchy foods (Bender and Bender, 1995).

Sources of starch

 

Plants manufacture carbohydrates by the process of photosynthesis. Photosyntheisi involves plants converting carbon dioxide gas from the atmosphere and water from the soil into a simple sugar by utilizing the energy from sunlight in the presence of the green pigment called Chlorophyll (Jacoby and Youngson, 2005). The sugar is soluble in water and is transported to the parts of the plant that need energy for growth or repair. The excess sugar is converted into insoluble starch and stored, ready to be converted back into sugar when the plant needs it. Plants such as potatoes that have a large storage capacity therefore contain a large quantity of starch (Bender and Bender, 1995).

 The Digestion of Starch

 

The process of digesting starchy foods begins in the mouth. Food is first broken into manageable pieces by the teeth and mixed with the saliva produced by the salivary glands in the mouth. The saliva contains a starch-digesting enzyme called Ptyalin, or Amylase, which is capable of breaking down the starch into simpler sugars. There is, however, little time for the starch-digesting enzyme to act before the food is swallowed and passed into the stomach. In the stomach there is no digestion of carbohydrates (Jacoby and Youngson, 2005).

When the stomach contents are passed into the duodenum, or small intestine, enzymes from the pancreas continue to break down all carbohydrates into the simple sugars like glucose that make them up. This end product of digestion is absorbed into the body, enters the hepatic portal vein, and is transported to the liver before entering the bloodstream.

The liver and glycogen

 

In the same way that plants store starch for use when sugar supplies are low, the body also stores a small reserve of starch called glycogen, or animal starch.

Glucose absorbed in the small intestine can be converted to glycogen in the liver, which usually holds about 3.5 ounces (100 g). The muscles also contain substantial quantities. As glucose is used up in the body to provide energy, so the equivalent amount of stored glycogen is broken down by enzymes to glucose. In this way the concentrations of glucose in the blood and body fluids can be kept within limits (Jacoby and Youngson, 2005).

The deposition of glycogen and its reconversion to sugar are controlled by hormones, most importantly insulin from the pancreas. When people eat meals that contain a lot of starch and sugar, the amount of sugar in the blood can double within a matter of minutes. This rapid increase causes the pancreas to pour out insulin, which acts on the muscles and the liver and instructs them to withdraw sugar from the blood before it is lost in the urine, and to store it as the starch glycogen (Preferred Starch for Diabetics, 1986). However, the muscles and liver can store only a limited amount of starch; the excess is converted to fat and laid down in fatty tissue. If you were to compare fats with starches; fats store three times more energy than starch. Obesity is the result of excess intake over energy expenditure.

 

 

References

 

Bender, A.E. and Bender, D.A. (1995). A Dictionary of Food and Nutrition. Oxford University Press: Oxford.

 

Jacoby, D.B. and Youngson, R.M. (2005). Encyclopedia of Family Health: Volume 15. (Ed 3) New York.

 

Preferred Starch for Diabetics?. Science News. Volume: 130. August 2, 1986.

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