Structure and Functions (Magill’s Medical Guide, Sixth Edition)
Food biochemistry is concerned with the breakdown of food in the cell as a source of energy. Each cell is a factory that converts the nutrients of the food one eats to energy and other structural components of the body. The amount of energy that these nutrients supply is expressed in Calories (kilocalories). The number of Calories consumed will determine the energy balance of the individual and whether one loses or gains weight. The nutrients come in a variety of forms, but they can be divided into three major categories: carbohydrates, lipids (fats), and proteins. These nutrients are broken down by the cell metabolically to produce energy for cellular processes. Other components are used by the cell and the entire body for structure and transport. Each of these nutrients is essential to a well-balanced diet and good health. Two other components of a successful diet are vitamins and minerals.
Carbohydrates are molecules composed of carbon, hydrogen, and oxygen. They range from the simple sugars all the way to the complex carbohydrates. The simplest carbohydrates are the monosaccharides (one-sugar molecules), primarily glucose and fructose. The simple monosaccharides are usually joined to form disaccharides (two-sugar molecules), such as sucrose (glucose and fructose, or cane sugar), lactose (glucose and galactose, or milk sugar), and maltose (two glucoses, which is found in grains). The complex carbohydrates are the...
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Disorders and Diseases (Magill’s Medical Guide, Sixth Edition)
Diet plays a major role in the metabolism of the cells. One major problem in diet is the overconsumption of Calories, which can lead to weight gain and eventual obesity. Obesity is defined as being 20 percent over one’s ideal weight for one’s body size. A number of problems are associated with obesity, such as high blood pressure, high levels of cholesterol, increased risk of cancer, heart disease, and early death.
At the other end of the scale is malnutrition. Carbohydrates are the preferred energy source in the form of either blood glucose or glycogen, which is found in the liver and muscles. This source gives a person approximately four to twelve hours of energy. Long-term storage of energy occurs as fat, which constitutes anywhere from 15 percent to 25 percent of body composition. During times of starvation, when the carbohydrate reserve is almost zero, fat will be mobilized for energy. Fat will also be used to make glucose for the blood because the brain requires glucose as its energy source. In extreme starvation, the body will begin to degrade the protein in muscles down to its constituent amino acids in order to produce energy.
Malnutrition can also occur if essential vitamins and minerals are excluded from the diet. Vitamin deficiencies affect the metabolism of the cell since these compounds are often required to aid the enzymes in producing energy. A number of medical problems are associated with...
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
The study of food biochemistry has evolved over the years from a strictly biochemical approach to one in which diet and nutrition play a major role. An understanding of diet and nutrition required vital information about the metabolic processes occurring in the cell, supplied by the field of biochemistry.
This information started to become available in 1898 when Eduard Buchner discovered that the fermentation of glucose to alcohol and carbon dioxide could occur in a cell-free extract. The early twentieth century led to the complete discovery of the glycolytic pathway and the enzymes that were involved in the process. In the 1930’s, other pathways of metabolism were elucidated.
In conjunction with Buchner’s discovery, British physician Archibald Garrod in 1909 hypothesized that genes control a person’s appearance through enzymes that catalyze certain metabolic processes in the cell. Garrod thought that some inherited diseases resulted from a patient’s inability to make a particular enzyme, and he called them “inborn errors of metabolism.” One example he gave was a condition called alkaptonuria, in which the urine turns black upon exposure to the air.
Some of the earliest nutritional studies date back to the time of Aristotle, who knew that raw liver contained an ingredient that could cure night blindness. Christiaan Eijkman studied beriberi in the Dutch East Indies and traced the problem to...
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Bonci, Leslie. American Dietetic Association Guide to Better Digestion. New York: Wiley, 2003. A user-friendly guide to help analyze one’s eating habits, map out a dietary plan to manage and reduce the uncomfortable symptoms of digestive disorders, and find practical recommendations for implementing lifestyle changes.
Campbell, Neil A., et al. Biology: Concepts and Connections. 6th ed. San Francisco: Pearson/Benjamin Cummings, 2008. An introductory college textbook geared for the biology major but easily understood by the high school student. One chapter covers the process of digestion and nutritional requirements. References at the end of the chapter are provided for further reading. Contains useful tables and diagrams.
Clark, Nancy. Nancy Clark’s Sports Nutrition Guidebook. 4th ed. Champaign, Ill.: Human Kinetics, 2008. An easy-to-read book that covers the subject of nutrition for the sports-minded reader. Dispels a number of nutritional myths. Explores many applications of food biochemistry, and offers recipes and references in the appendix.
Duyff, Roberta Larson. American Dietetic Association Complete Food and Nutrition Guide. 3d ed. Hoboken, N.J.: John Wiley & Sons, 2007. Experts from the American Dietetic Association detail advances in nutrition research and provide authoritative answers to questions regarding food and nutrition.
(The entire section is 376 words.)