There are nutrients that do not provide calories, and with exceptions, have no influence on body composition, but which must nevertheless be consumed with food, or else diseases will occur. These nutrients are vitamins, minerals and water. Let us look at them in more detail. As for vitamins, they can be classified into fat-soluble and water-soluble, depending on their ability to dissolve in fat (the former) or water (the latter). Fat-soluble vitamins are:

1. vitamin A (retinol);
2. vitamin D (calciferol);
3. vitamin E (tocopherols);
4. vitamin K (menadione).

Water-soluble vitamins, on the other hand, are:

1. vitamin B1 (thiamine);
2. vitamin B2 (riboflavin);
3. vitamin PP (niacin);
4. vitamin B6 (pyridoxine);
5. vitamin Bc (folates);
6. vitamin B12 (cobalamin);
7. vitamin H (biotin);
8. vitamin B5 (pantothenic acid);
9. vitamin C (ascorbic acid);
10. vitamin T (carnitine);
11. vitamin P (bioflavonoids);
12. vitamin B15 (pangamic acid).

As for minerals, they are:

1. calcium (Ca);
2. phosphorus (P);
3. magnesium (Mg);
4. sodium (Na);
5. potassium (K);
6. chlorine (Cl);
7. iron (Fe);
8. zinc (Zn);
9. copper (Cu);
10. selenium (Se);
11. iodine (I);
12. manganese (Mn);
13. molybdenum (Mo);
14. chromium (Cr);
15. fluorine (F);
16. cobalt (Co).

Vitamina A

  In nature, vitamin A exists in three different forms: retinol, retinaldehyde and retinoicacid. Each of these three forms can only be taken from animal sources. This does not mean that a vegetarian person is destined to be deficient in this micronutrient. In fact, some plant-based foods contain vitamin A precursors: carotenoids (the most common of which is β- carotene or beta-carotene). By consuming carotenoids, the body can obtain the vitamin A it needs from them. Nevertheless, only a third of the β-carotene taken in through the diet is absorbed in the intestines (the rest is excreted in the faeces). And of that share, only half is used to produce retinol. On the other hand, it is also true that one molecule of β-carotene can yield two molecules of retinol. The main biological function of retinol is related to vision. In fact, certain parts of the eye (the optic receptors of the retina, i.e. the cones and rods) are made up of retinol. The diet should always include a good source of vitamin A or carotenoids.

Vitamin D

  Vitamin D is the generic term for a number of different compounds. Of these, the one that occurs naturally and can be ingested through food is calciferol. Ergocalciferol, on the other hand, is formed in the skin following exposure to sunlight. Nutritionists have often underestimated the importance of taking foods that are sources of vitamin D, because they believed that humans could synthesise ergocalciferol simply by exposing themselves to sunlight. In reality, however, presumably because very little time is spent outdoors in sunlight nowadays, the ergocalciferol that can be produced is rather low. Vitamin D, regardless of whether it is in the form of ergocalciferol or calciferol, is of great importance in calcium and phosphorous metabolism. More specifically, it promotes the absorption of calcium in the intestines, regulates the reabsorption of calcium and phosphorous in the kidneys and the deposition of calcium in bone tissue (as we shall see, bones are mostly made of calcium and, in the absence of vitamin D, this cannot be deposited properly to consolidate the structure of the skeleton).

Vitamin E

  How vitamin E works in the body is not yet clear to researchers, but it is known that it has an antioxidant role. In other words, it can prevent the occurrence of tumours. It is extremely important that the diet includes sources of vitamin E.

Vitamin K

  Vitamin K is the inactive form of hydroquinone. In other words, vitamin K, under certain conditions, is converted within the body to hydroquinone, which regulates blood coagulation (the process by which, when one injures the skin, the blood gives rise to the formation of those typical scabs that later become new skin tissue) and the transport of certain important substances within the blood. Hydroquinone is also important for the metabolism of bone tissue.

Vitamin B1

  Vitamin B1 is the precursor of two important substances: thiamine pyro-phosphate and thiamine tri-phosphate. The former is important in energy metabolism (especially glucose metabolism), i.e. it helps certain enzymes to derive energy from macronutrients. Thiamine tri-phosphate, on the other hand, is useful to the liver, in the absence of which the liver becomes unable to regulate the permeability of channels for the chlorine ion. It is therefore extremely important that it is available in the required quantity.

Vitamin B2

  Vitamin B2 is, in its biologically active form (FMN or flavin-mono-nucleotide and FAD or flavin-adenin-dynucleotide), essential for the regulation of energymetabolism. Like vitamin B1, therefore, B2 also serves the body to obtain energy from carbohydrates, proteins and fats.

Vitamin PP

  The biologically active forms of vitamin PP are NAD (nicotinamide-adenine dinucleotide) and NADP (nicotinamide-adenine dinucleotide phosphate). Like FAD (the active form of vitamin B2) and thiamine pyro-phosphate (the active form of vitamin B1) they exert their action on energy metabolisms.

Vitamin B6

  Vitamin B6 has three biologically active forms: pyridoxine, pyridoxal and pyridoxamine. These molecules perform multiple functions within the human body. Specifically:

1. they regulate the metabolism of amino acids (which, remember, are the constituent units of proteins);
2. convert linoleic acid (a fat) into arachidonic acid (another fat);
3. are responsible for the formation of many neurotransmitters, i.e. those substances that mediate communication between the different cells of the nervous system;
4. are responsible for the formation of those particular fats, called sphingolipids, of which the sheath that surrounds the terminal parts of nerve cells is made;
5. contribute to the breaking of particular chemical bonds, called glycosidic bonds, which must be broken;
6. contribute to the production of haemoglobin, the substance responsible for transporting oxygen in the blood;
7. modulate the activity of steroid hormones (such as testosterone).

It should be noted that the easiest pyridoxine to digest and absorb (i.e., the most bioavailable form) is found in foods of animal origin. In other words, a good amount of the pyridoxine contained in plant-based foods will not be digested and absorbed, but will instead be excreted with faeces. Nevertheless, even a vegetarian diet is compatible with a good level of pyridoxine intake. In fact, the incidence of diseases related to a low intake of pyridoxine is very low even among vegetarians. This proves that values taken solely from plant sources are sufficient to cover one’s requirements.

Vitamin Bc

  Tetrahydrofolic acid is the biologically active form of vitamin Bc. When the latter is transformed into the former, it helps regulate the metabolism of amino acids and nucleic acids (DNA and RNA).

Vitamin B12

  The biologically active forms of vitamin B12 are 5′-deoxyadenosyl-cobalamin and methyl-cobalamin. The former is involved in the conversion of methyl-malonyl-CoA to succinyl-CoA (a reaction mediated by the enzyme methylmalonyl-CoA mutase) and is involved in the metabolism of nucleic acids (DNA and RNA). Succinyl-CoA is an intermediate product of the Krebs cycle, which has already been encountered several times.  The second, on the other hand, is involved, aided by methyltetrahydrofolate, in the conversion of homocysteine to the amino acid methionine (a reaction mediated by the enzyme homocysteine methyltransferase).

Vitamin H

  Contrary to what one might think, vitamin H also belongs to the B vitamins. It functions as a coenzyme for various enzymes (carboxylases). In other words, it helps certain enzymes to fulfil their role of catalysing chemical reactions.

Vitamin B5

  Pantothenic acid is the precursor of coenzyme A (CoA), which plays an important role in the metabolism of carbohydrates, proteins, fats and steroid compounds. It is also one of the constituent parts of the acyl carrier protein, which is an important transport protein for fatty acid synthesis.

Vitamin C

  Vitamin C, or ascorbic acid, performs various functions within the humanbody:

1. participates in the formation of new molecules of the hormone noradrenaline;
2. contributes to the formation of new collagen, a specific protein;
3. contributes to the formation of new bile acids, substances needed for fat digestion;
4. participates in the formation of new molecules of carnitine, another vitamin (more on this in a moment);
5. contributes to the formation of new steroid hormone molecules;
6. contributes to the formation of the hormone known as humoral thymic factor;
7. participates in the formation of certain classes of antibodies, i.e. those substances designed to protect the body from attacks by various microbes and pathogens;
8. can activate vitamin Bc;
9. regulates the amount of histamine (a substance responsible for allergic reactions) that is produced;
10. deals with the catabolism (dismantling) of a particular amino acid: tyrosine;
11. is responsible for some important transformation processes of certain hormones;
12. is responsible for intestinal absorption of iron;
13. is responsible for reducing intestinal absorption of copper;
14. is responsible for reducing the toxicity of certain minerals;
15. is responsible for increasing the bioavailability of selenium;
16. has an antioxidant and cancer-preventive effect;
17. can help preserve muscle integrity, thus preventing damage to the fibres that make up the muscles;
18. can stimulate the production of interferons (particular proteins of the immune system);
19. can stimulate the proliferation of neutrophils (important cells also belonging to the immune system).

Vitamin T

  The main role of vitamin T, also known as carnitine, is to transport fatty acids into muscle cells so that they can use them to produce the energy they need. However, it also has a stimulating function on the central nervous system.

Vitamin P

  This vitamin assists vitamin C in maintaining collagen in good condition and strengthens the structure of blood vessels with less robust and more permeable walls: the capillaries.

Vitamin B15

  The function of vitamin B15 is not yet well known to science. For some, it may assist the immune system in performing its functions. It should be noted, however, that according to some, vitamin B15 may also have harmful functions.

Calcium

  Calcium is one of the constituents of the hydroxyapatite crystals from which bones are made. In other words, calcium is the mineral that gives solidity and hardness to bone tissue. It is also involved in the process of muscle contraction. It should be noted that the bioavailability of calcium is improved by protein intake (Klesges, 1996; Guillemant, 2004).

Phosphorus

  Like calcium, phosphorus is a constituent of hydroxyapatite crystals in bones. It also performs several structural functions and is able to regulate the pH of body fluids.

Magnesium

  This mineral has various biological functions, including:

1. the mediation of a reaction whereby ATP (chemical energy) and pyruvate are obtained from ADP and phosphoenolpyruvate;
2. is involved in glycolysis, that chemical reaction whereby a glucose molecule is split into two pyruvate molecules;
3. is a cofactor of alkaline phosphatase, an enzyme that catalyses the removal of phosphate groups;
4. intervenes in DNA metabolism;
5. intervenes in the Krebs cycle;
6. activates the enzyme adenosine triphosphatase, which is involved in maintaining the concentration gradient of potassium inside and outside the cells (i.e. it regulates the balance between the amount of potassium present in the intracellular spaces and that contained in the extracellular spaces).

Sodium

  Sodium is important for regulating certain fluid parameters between the various cells in the body. It also plays an important role in the process of muscle contraction.

Potassium

  Potassium plays multiple roles within the human body:

1. regulates the rhythmicity with which the heart beats;
2. check that the amount of water in the body is optimal;
3. regulates the pH of body fluids;
4. plays a role in muscle contraction;
5. plays a controlling role on blood pressure.

Chlorine

  Chlorine contributes to maintaining the water-salt balance and to the formation of hydrochloric acid, which acidifies the stomach so that food digestion can take place.

Iron

  The main biological role of iron is to take part in the structure of haemoglobin and myoglobin. The former, as we have already seen, is the molecule responsible for transporting oxygen in the blood. The second, on the other hand, is responsible for storing this element within the muscles. The iron contained in food can be of two different types:

1. heme (or hemeic) iron, i.e. that which comes from foods of animal origin;
2. non-heme (or non-hemeic) iron, i.e. from plant foods.

The former consists of a ferrous ion (i.e. bivalent, with two unpaired electrons) bound to a particular molecule called protoporphyrin; the latter can be either in the ferrous state, as in heme, or in the ferric state (i.e. trivalent, with three unpaired electrons). Non-heme iron is slightly more bioavailable in its ferrous form than in its ferric one, but still, even if bivalent, absorption levels are a long way from those of heme iron. Now, while this is true on the one hand, it is also true that many foods of plant origin contain more than double the amount of iron contained in foods of animal origin. The poor quality of iron of plant origin can therefore be compensated for by the higher intake. In addition, by taking iron-rich foods together with foods rich in vitamin C (e.g. lemon, peppers), as the latter assists the absorption process of this mineral, it is possible to bring the bioavailability of non-eme iron closer to that of iron from animal sources.  Iron deficiency in vegetarians is therefore far from obvious.

Zinc

  Zinc also has multiple functions within the body:

1. is a component of the structure of numerous enzymes;
2. collaborates with selenium and iodine in the metabolism of steroid hormones;
3. maintains the configuration of certain proteins;
4. facilitates the maturation of immune system cells produced by the thymus (a gland);
5. has antioxidant-type activity. It therefore prevents the occurrence of tumours;
6. is necessary for bone and muscle formation.

Copper

  The functions of copper within the human body can be summarised asfollows:

1. It supports the functions of cell metabolism;
2. plays a role in the formation of new molecules of catecholamines (special hormones) and enkephalins (neurotransmitters);
3. collaborates in building new connective tissue (the type of tissue that provides structural support to other tissues);
4. guarantees the full functionality of the heart;
5. intervenes in the synthesis of haemoglobin, in conjunction with iron;
6. takes part in pigmentation (colouring) and keratinisation of the skin and hair. The latter is the process of adding keratin (a protein) to the structure of skin and hair.

Selenium

  Quite simply, selenium has an antioxidant function, i.e. it prevents the occurrence of tumours.

Iodine

  Iodine is a structural component of thyroid hormones. The biological role of this element, therefore, is primarily linked to the activity of these hormones.

Manganese

  The main biological role of manganese is related to the activation of various enzymes, which, without this mineral, could not perform their function. These enzymes include hydrolases, isomerases, oxidoreductases, transferases, lyases, ligases, lectins and integrins. It is also present in certain polypeptides (chains of amino acids). Manganese is therefore important for various biological functions, including blood coagulation, immune system activity, blood glucose regulation, thyroid activity, etc.

Molybdenum

  Molybdenum has the function of assisting three enzymes: xanthine oxidase, aldehyde oxidase and sulphite oxidase. The first degrades hypoxanthine first into xanthine and then into uric acid; the second metabolises aldehydes produced by metabolism; the third oxidises sulphite ions into sulphate ions.

Chromium

  Chromium’s main biological role is to enhance insulin activity by reducing the amount needed to regulate blood glucose.

Fluorine

  Researchers have not yet clarified exactly what the biological role of fluoride is, but it was found that in those who consumed a fair amount of fluoride, the incidence of dental caries was significantly lower than in everyone else. For some, fluoride would also play a role in bone mineralisation.

Cobalt

  Cobalt is a trace element that is usually introduced with vitamin B12, as it is a constituent of it. Its biological role is related to the function of nucleic acids (DNA and RNA), whose enzyme complexes it is part of.

Water

  Water accounts for 60-70% of body weight in men and women. By virtue of this alone, the importance of proper hydration of the human body should be clear. Let us see, then, what the biological roles of water are:

1. helps regulate body temperature, stabilising it around 37°C;
2. plays a role in the regulation of cell volumes;
3. It assists in the removal of metabolic waste from cells and the transport of nutrients within them;
4. is a source of mineral salts (which is quite easy to find by checking the label of any bottle of mineral water);
5. can increase cellular metabolic activity within certain limits, which also has an impact on the body’s calorie expenditure.

The water requirement (preferably natural) is about 2-2.5l per day.