Nutrição

Fundamentos de Nutrição
Vitamins Vitamins do not supply the body with energy in the form of calories- a fact that distinguishes them from fat, carbohydrate, and protein. However, many vitamins regulate the chemical reactions that allow us to obtain energy from those nutrients. Vitamins differ from fat, protein, and carbohydrate in other important ways. For one, the amounts of vitamins a bodyneeds daily-a mere microgram or in some cases-are infinitesimal compared to the grams of fat, carbohydrate, and protein required each day. Another difference is structural: vitamins are individual units rather than long chains of smaller units. Like fat, carbohydrate, and proteins, however, vitamins are organic (carbon-containing) compounds essential for normal functioning, growth, and maintenance ofthe body. Aula 5

Fundamentos de Nutrição
Vitamins Vitamins A, D, E, and K are lipid-like molecules that are soluble in fat. The B vitamins and Vitamin C, on the other hand, are soluble in water. This difference in solubility affects the way the body absorbs, transports, and stores vitamins .

Aula 5

Fundamentos de Nutrição
Vitamins Intestinal cells absorb fat-soluble vitamins alongwith dietary fat. The amount absorbed typically varies from 40 to 90 percent of the amount consumed; efficiency of absorption generally falls as the dietary intake rises above the body's needs. Just like triglycerides and other dietary lipids, lipoproteins carry absorbed fat-soluble vitamins on their journey through the lymph and bloodstream. As chylomicrons move through the blood, cells take upmost of the triglycerides and leave behind chylomicron remnants that contain the fat-soluble vitamins. The liver picks up these remnants and either stores the vitamins for future use or repackages them for delivery via the bloodstream to other tissues.

Aula 5

Fundamentos de Nutrição
Vitamins Water-soluble vitamins are dissolved in the watery compartments of foods. Once absorbed, thesenutrients travel directly into the bloodstream and then move independently in and around the cells of the body. Unlike fat-soluble vitamins, watersoluble vitamins do not need lipoprotein carriers. Their storage and excretion differ, too. While most fat-soluble vitamins accumulate and can be stored indefinitely, the kidneys filter out excess amounts of most water-soluble vitamins and excrete them inurine. Two vitamins are exceptions to this general rule: water-soluble vitamin B12 is stored more readily than the other watersoluble vitamins, and fat-soluble vitamin K is excreted more readily than the other fatsoluble vitamins. Aula 5

Fundamentos de Nutrição
Vitamins – Storage and toxicity Fat-soluble vitamins accumulate in the liver and adipose tissues, where they can be drawn upon in times ofneed. Once these vitamin stores are established, you can go for days, weeks, or even months without consuming more and suffer no ill effects. On the other hand, excessive intake of the fat-soluble vitamins A or D can exceed the body's storage capacity, with toxic effects. Your body does not store most water-soluble vitamins in appreciable amounts, so they should be a part of your daily diet.Small variations in daily/ intake typically do not cause problems, however. For example, it takes 20 to 40 days of a diet deficient in the water-soluble vitamin C before deficiency symptoms emerge. Consuming excess water-soluble vitamins usually is harmless, since your body simply excretes the surplus. However, large amounts of some water-soluble vitamins (like vitamin B6) can cause permanent damage.Vitamin toxicity is rarely linked to high vitamin intakes from food or to the use of supplements that contain 100 to 150 percent of the recommend amounts. People who take megadoses of one or more vitamins run a high risk of toxicity.

Aula 5

Fundamentos de Nutrição
Vitamins – Provitamins Certain vitamins in foods are in inactive forms that the body cannot use directly. These substances...
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