Vitamins in the Diet

Which nutrient is recommended to be decreased in a healthy diet  

Which kinds of foods are recommended to be increased in a healthy 

A major goal in a healthy diet is to have no more than % of food Calories from fat. 

A vitamin is an organic compound essential to health that must be supplied in small amounts by the diet. Vitamins provide no energy and are unchanged by digestion. The body does not synthesize vitamins, but needs them to function as coenzymes. There are two kinds of vitamins, fat soluble and water soluble. 

The fat-soluble vitamins—A, D, E, and K—can be stored in the fatty tissues of the body (especially the liver). They have nonpolar hydrocarbon chains and rings that are compatible with nonpolar oils and fats. It is important to store enough fat-soluble vitamins, but not too much because excesses are not excreted and can be toxic. 

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Toxicity of cadmium increases in cases of zinc deficiency, due to the zinc substitution in biological systems, which leads to functional disorders. Cadmium reduces assimilation of vitamins C and D. However, a large amount of these vitamins in the diet will decrease the toxicity of cadmium through the reduction of its absorption from the intestinal tract (Friberg et ah, 1986 Hill, 1996 McLaughlin et ah, 1999). 

Given this structural similarity, it should not be surprising to learn that sulfanilamide competes with p-aminobenzoic acid for a binding site on the surface of dihydropteroate synthetase. Put another way, sulfanilamide binds to the enzyme where p-aminobenzoic acid should bind but no reaction occurs. The consequence is that a step in folic acid biosynthesis is disrupted and the bacterial cell is deprived of adequate folic acid. Nucleic acid synthesis, among other things, is disrupted, leading to a cessation of cell growth and division. The human immune system can mop up what remains. No similar consequences befall the human host since it cannot make folic acid in the first place and must get an adequate supply of this vitamin in the diet. 

Vitamin K was discovered in 1935 as a result of studies of a hemorrhagic disease of chickens fed on solvent-extracted fat-free diets and cattie fed on silage made from spoiled sweet clover. The problem in the chickens was a lack of the vitamin in the diet, whereas in the catde it was from the presence of di-coumarol, an antimetabolite of the vitamin. It soon became apparent that vitamin K was required for the synthesis of several of the proteins required for blood clotting, but it was not until 1974 that Stenflo and coworkers (1974) elucidated the mechanism of action of the vitamin. A new amino acid, y-carboxyglutamate (Gla) was found to be present in the vitamin K-dependent proteins, but absent from the abnormal precursors that circulate in deficiency. y-Carboxyglutamate is chemically unstable and undergoes spontaneous decarboxylation to glutamate when proteins are hydrolyzed in acid for amino acid analysis. 

Vitamin B6 is required for the formation of pyridoxal phosphate, an important cofactor in nitrogen metabolism. Deficiencies of vitamin B6 are caused by a lack of the vitamin in the diet or by the administration of drugs such as isoniazid, which interfere with its metabolism. Synthesis of neurotransmitters, NAD, and heme are decreased, resulting in neurologic and pellegra-like symptoms and anemia. 

It is sometimes difficult to calculate the RE because, in order to determine the actual content of vitamin A in food products, meals, or daily food allowance, it is necessary to first determine the content of retinol, P-carotene, and other carotenoids, and only then calculate the RE. Currently, recommended dietary allowances (RDA) are being proposed to ensure that there are appropriate quantities of individual vitamins in the diet to cover the organism s demand. The recommended doses are subject to modification and take into consideration changing life conditions and dietary patterns. In addition, increasing knowledge of human nutrition makes it necessary to update them from time to time (Russell, 1997). 

Even though vitamins are required only in very small quantities, to ensure that the adequate intake of vitamins in the diet is received, people can consume foods eruriched with vitamins, for example, in the form of functional foods with vitamins as nutraceuticals. In addition, certain vitamins extracted from natural sources such as seaweeds have antioxidant activity and other health benefits such as decreasing of blood pressure, prevention of cardiovascular diseases, or reducing the risk of cancer. 

Although the 20 amino acids and complex folding patterns open up a range of chemical possibilities to proteins, there are also many limitations. In order to widen the range of chemistry available to enzyme catalysts, we make use of auxiliary compounds particularly well suited to certain types of reaction (Fig. A6.1). Thus NAD+, NADP+ and FAD are nucleotide cofactors based on the stmctures of nicotinamide and riboflavin, and are used for oxidation-reduction reactions. Biotin is used for carboxylation, pyridoxal phosphate is used for transamination and decarboxylation and so on. As mentioned in Box 3 (Topic 10), most of these are derived from vitamins in the diet. 

Like metal ions, the small organic molecules that act as coenzymes bind reversibly to an enzyme and are essential for its activity. An interesting feature of coenzymes is that many of them are formed in the body from vitamins (see > Table 10.2), which explains why it is necessary to have certain vitamins in the diet for good health. For example, the coenzyme nicotinamide adenine dinucleotide (NAD ), which is a necessary part of some enzyme-catalyzed oxidation-reduction reactions, is formed from the vitamin precursor nicotinamide. Reaction 10.5 shows the participation of NAD in the oxidation of lactate by the enzyme lactate dehydrogenase (LDH). Like other cofactors, NAD is written... 

In most cases, pernicious anemia does not result from the absence of vitamin in the diet. The vitamin is abundant in diets that include meat, milk, and eggs. However, plant leaves are low in vitamin Bjp, and therefore symptoms suggestive of vitamin B p deficiency have been observed among confirmed vegetarians. Generally, however, the main cause of vitamin Bi2 deficiency is interference with its use [83-88]. 

Animal protein concentrates are used primarily in small amounts to make good deficiencies of certain Indispensable amino acids, minerals and B vitamins in the diets of non-ruminant animals. 

Thiamine hydrochloride is structurally similar to thiamine pyrophosphate (TPP). TPP is a coenzyme universally present in all living systems. It catalyzes several biochemical reactions in natural systems. It was originally discovered as a required nutritional factor (vitamin) in humans by its link with the disease beriberi. Beriberi is a disease of the peripheral nervous system caused by a deficiency of Vitamin in the diet. Symptoms include pain and paralysis of the extremities, emaciation, and swelling of the body. The disease is most common in Asia. 

The need for vitamins can also be affected by the presence of other food components that can interfere with vitamins in the diet. These substances are called antivitainins or vitamin anti onists. Antivitamins eliminate the biological effects of vitamins, which can lead to symptoms of deficiency. The activity of antivitamins is based on the following basic principles ... 

Secondly, foodborne nutrients may in certain cases be present in combinations which work together. For example, the metabolic activities of the members of the vitamin B complex are interrelated. Hence, the failure to provide sufficient dietary quantities of one or more of these vitamins may impair the functions of other B vitamins in the diet. 

Deficiency symptoms— The absence of one or more vitamins in the diet may lead to failure in growth or reproduction, or to characteristic disorders known as deficiency diseeises. In severe cases, death may follow. The sign of a fat-soluble vitamin deficiency can sometimes be related to the function of the vitamin. For example, vitamin D is required for calcium metabolism and a deficiency results in bone abnormalities. On the other hand, the signs of a B-vitamin deficiency are... 

VITAMIN CONTENT OF FOODS. The vitamin content of foods is given in Food Composition Table F-21. However, in selecting foods to furnish vitamins in the diet, it is well to keep in mind the following ... 

The establishment of allowances for vitamin B-6 is complicated by the following facts (1) the requirement varies with dietary protein intake—there is increased need for vitamin B-6 with increased intakes of protein (2) the uncertainty of the availability of the vitamin in the diet and (3) the uncertainty as to the extent of intestinal bacterial synthesis of the vitamin, and the degree to which it is utilized by the body. Also, there is evidence of increased need of the vitamin in pregnancy and lactation, in the elderly, and in various pathologic and genetic disturbances. Nevertheless, the NRC has set recommended allowances to assure a safety margin and to make a deficiency unlikely under most circumstances. Discussion follows ... 

In 1919, Steenbock suggested that the fat-soluble vitamin A was related in some way to the carotinoids because of the similarity of distribution in natural sources. Inadequate knowledge of the properties of the vitamins delayed confirmation of the hypothesis, until, in 1929, von Euler showed that although carotene was not identical with vitamin A, it could replace the vitamin in the diet. Moore subsequently demonstrated that the pigment was transformed into the vitamin within the liver of the animal. Meanwhile, the carotenes had been resolved into their isomers, and it was found that -carotene had twice the provitamin potency of -carotene. Since the formula of vitamin A was known approximately to be C2oH29 OH, it was suggested that the vitamin was hydroxy-semf-jS-carotene, two molecules of which were derived from one molecule of 3-carotene by hydrolytic fission. 

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