1. What is a nutrient?
A nutrient is every substance used in the metabolism and which is acquired from the diet. For example, vitamins and essential amino acids are nutrients.
2. What is the difference between macro and micronutrients?
The classification criterion of nutrients into macro and micronutrients has no relation to the size of the molecule. Macronutrients are those needed in great amount, for example, proteins and carbohydrates. Micronutrients are those needed in small quantities, like vitamins.
3. According to their functions how can nutrients be classified?
One possible and utile functional classification for nutrients is the one that separates them into energetic, structural and regulatory.
Energetic nutrients are those used as energy source for the metabolism; mainly they are the carbohydrates (but fats and proteins can also be converted into acetyl-CoA and “cycle” the Krebs cycle). Structural nutrients are those used in the support and structure of cells and tissues; they are the amino acids that form structural proteins, like collagen, the membrane proteins, the cytoskeleton proteins, the contractile proteins of the muscle tissue, etc. Regulatory nutrients are those that constitute enzymes and coenzymes of the homeostasis, metabolites of the osmotic and electrolytic equilibrium of cells and hormones; some amino acids, vitamins and mineral salts are part of this group.
4. What are vitamins? What are the main vitamins needed by humans?
Most vitamins are coenzymes (fundamental substances for the enzyme functioning) that are not produced by the organism and must be obtained from the diet.
The main vitamins needed by humans are vitamins A, C, D, E, K, the vitamins of the B complex (including folic acid), biotin and pantothenic acid.
5. What is the difference between water-soluble and fat-soluble vitamins? Why can fat-soluble vitamins cause harm when ingested in excess?
Water-soluble vitamins are those soluble in water. Fat-soluble vitamins are those soluble in oil (lipids, fat). Vitamin C and the vitamins of the B complex are examples of water-soluble vitamins. Vitamins A, D, E and K are examples of fat-soluble vitamins.
Fat-soluble vitamins, since they are not soluble in water, cannot easily be excreted by the body. So they tend to accumulate in tissues with toxic effect when they are ingested in amounts over what is necessary.
6. What are the main harms caused by vitamin A deficiency? How does this vitamin act in the physiology of vision?
Deficiency of vitamin A (retinol) may cause night blindness, corneal dryness (xerophthalmia) and predisposition to skin injuries.
In the physiology of vision, vitamin A participates in the formation of rhodopsin, a pigment responsible for the visual perception in less illuminated places.
Nutrition Vitamins - Image Diversity: vitamin A deficiency
7. What is folic acid? Why is the anemia caused by deficiency of folic acid known as megaloblastic anemia?
The folic acid (when ionized it is called folate) is a coenzyme that participates in the synthesis and duplication of DNA and for this reason it is fundamental for cell division. If there are not enough folic acid in cells with great turnover, like red blood cells, they have their production reduced.
In folic acid deficiency precursor cells (reticulocytes) that would originate erythrocytes (red blood cells) begin cell division but the process is very slow while the cytoplasm growth is normal. So the cells became abnormally large, a typical feature of this kind of anemia called megaloblastic anemia.
Megaloblastic anemia can be caused also by vitamin B12 (cyanocobalamin) deficiency since this vitamin is important for cell division too. Both types of anemia are nutrient deficiency anemias.
Nutrition Vitamins - Image Diversity: megaloblastic red blood cell
8. What are the vitamins which make up the B complex? Which problems does the lack of these vitamins cause?
Vitamins of the B complex are: thiamin, or vitamin B1; riboflavin, or vitamin B2, and niacin (B3), essential for the constitution of the hydrogen acceptors FAD, NAD and NADP of the energetic metabolism; pyridoxine, or B6; and cyanocobalamin, or vitamin B12.
Deficiency of vitamin B1 causes beriberi, loss of appetite and fatigue. The lack of vitamin B2 causes mucosal injuries in the mouth, tongue and lips. Deficiency of niacin causes nervousness, digestive disturbances, loss of energy and pellagra. Lack of vitamin B6 causes skin lesions, irritation and convulsions. Vitamin B12 acts together with folic acid and its deficiency causes cell division disruptions leading to pernicious anemia (a type of megaloblastic and nutrient deficiency anemia).
The absorption of vitamin B12 depends on another substance called the intrinsic factor secreted by the gastric mucosa.
Nutrition Vitamins - Image Diversity: pellagra
9. How does vitamin C act in the body? What is the harm caused by insufficiency of vitamin C? Why was this deficiency also known as “sailors' disease”?
Vitamin C, or ascorbic acid, participates in the metabolism of collagen and it is fundamental for the integrity of blood capillaries.
Scurvy is the disease caused by a lack of vitamin C. It is characterized by tissue lesions in the skin, lips, nose and joints. Scurvy, or scorbutus, was also known as sailors' disease because in maritime voyages of the past it was not common to get on board food that contained vitamin C, like citric fruits. So the sailors became ill with scurvy.
Nutrition Vitamins - Image Diversity: scurvy
10. Why isn't the cooking of vitamin C-containing foods appropriate for vitamin C supply?
To obtain vitamin C, for example, from an orange dessert, the vitamin-containing food cannot be submitted to high temperatures (cooking) since vitamin C is thermolabile, i.e., it is inactivated by heat.
11. What is the association between vitamin D and sunrays?
Vitamin D, or calciferol, is synthesized in the skin by the action of the ultraviolet range of sunrays upon precursor molecules. Later it is transformed into its active form in the liver and the kidneys.
Nutrition Vitamins - Image Diversity: vitamin D synthesis
12. What is the disease caused by vitamin D deficiency? Which tissue does it affect?
The lack of vitamin D causes the disease known as rickets (rachitis), characterized by decalcification of bones and bone deformities. Vitamin D is fundamental for absorption of calcium and thus it is related to the osseous tissue health.
Nutrition Vitamins - Image Diversity: rickets
13. What is the function of vitamin E? In which foods can it be found?
Vitamin E, or tocopherol, is a fat-soluble vitamin that participates as coenzyme in the respiratory chain, the final stage of the aerobic cellular respiration. Its deficiency may cause sterility, spontaneous abortions and muscle dystrophy.
Vitamin E is mainly found in corn oil and peanut oil, wheat germ, milk, eggs and leafy vegetables.
14. Why are some types of hemorrhagic diseases caused by genetic or acquired deficiency of the vitamin K metabolism?
Deficiency of vitamin K predisposes to hemorrhages since this vitamin is fundamental for the formation of prothrombin in the blood clotting process.
15. What are the functions of biotin and pantothenic acid for the body? How are these vitamins obtained?
Biotin (also know as vitamin B8) is a vitamin that acts in the metabolism of amino acids and other acids. Pantothenic acid (also known as vitamin B5) is important for the aerobic cellular respiration since it acts in the transport of acetyl and acyl radicals.
Biotin is made by bacteria that live in the human digestive tube (under interspecific harmonious ecological interaction) and this supply in general is enough for the body. Biotin and pantothenic acid are found in vegetables, cereals, eggs, fish, milk and lean meat.
16. What are the main mineral salts responsible for the cellular osmotic regulation?
The main ions that act in the regulation of the osmotic pressure in cells and tissues are the chlorine anion, the sodium cation and the potassium cation.
17. What are the main cellular functions of potassium?
Besides being important for the osmotic regulation and for the acid-base equilibrium (pH) potassium is fundamental for the excitatory mechanisms of nerves and in muscle contraction.
18. What are some examples of mineral salts from the diet that act as coenzymes?
Magnesium, zinc and copper are examples of biological coenzymes.
19. What is the disease caused by dietary iodine deficiency?
Iodine deficiency causes hypothyroidism, an abnormally lower production of thyroid hormones that need iodine to be synthesized.
Nutrition Vitamins - Image Diversity: thyroid goiter
20. What is the importance of iron in diet? What is the disease caused by iron deficiency?
Iron acts as a constituent of the hemoglobin molecule and of enzymes of the digestion and energetic metabolism. Dietary iron deficiency causes iron deficiency anemia, abnormal lowering of hemoglobin concentration in blood due to lack of iron. (In pregnancy there is a high consumption of iron by the fetus and this fact can lead to anemia.)