The building blocks of food - Nutrition




The building blocks of food

The macronutrients The micronutrients The trace elements
  • Macronutrients
    • Carbohydrates
    • Lipids
    • Protein
  • Micronutrients
  • Trace elements

Nutrition, which is a phenomenon common to all living beings, aims to introduce and assimilate the substances essential for the maintenance of vital functions. These substances are divided into two large groups:

  • macronutrients, needed in quantities of tens or hundreds of grams per day;
  • micronutrients, which instead serve in much more limited quantities, from a few milligrams to micrograms.

Go back to the menu


Macronutrients are carbohydrates, lipids and proteins. The first two represent the main sources of energy for the body: that is, they perform an energetic function, allowing the various systems and apparatuses to have the "fuel" necessary to fulfill all their functions. Proteins provide the material needed for the maintenance and growth of organic structures: therefore they are said to perform a plastic function. In reality, carbohydrates and lipids also perform structural functions to a small extent; in fact, just like proteins, they can be used by our cells to obtain energy.

Go back to the menu


They are also called sugars or carbon hydrates. Their energy power is 4 kilocalories per gram. In some cases they consist of small molecules formed by a low number of carbon, oxygen and hydrogen atoms: these are simple sugars, for example fructose (fruit sugar), glucose (also present in the blood), sucrose ( the common sugar we use to sweeten, obtained from beet or sugar cane) and lactose (milk sugar).

In other cases, carbohydrates are made up of very large molecules, the result of the union of thousands of glucose molecules: these are polymers, long repetitions of simple sugars, which are called polysaccharides or complex carbohydrates. Among these, the most important substance for nutritional purposes is starch.

In order for starch and other complex sugars to be absorbed by the intestine, they must be fragmented into the individual glucose molecules of which they are made: this is possible thanks to the action of enzymes, the so-called amylases, mainly produced by the pancreas but present in different quantities along most of the enteric canal, from the mouth to the small intestine.

Foods containing starch are those based on cereals (bread, pasta, polenta, rice and so on) and vegetables such as potatoes, legumes and bananas.The difference between simple and complex sugars is often emphasized, considering the first sources of damage to health and the latter, on the contrary, benefits. It is precisely based on this schematism that some guidelines recommend that simple sugars do not make up more than 10% of daily calories (i.e. no more than 50-60 g per day). Like all simplifications, this too is a source of errors: for example, an excessive use of foods containing refined sugars as sweeteners increases the risk of tooth decay, predisposes to an excessive caloric introduction (especially in the form of sugary drinks) and in addition it promotes the increase in plasma of triglycerides and uric acid. It is good to keep in mind that milk, vegetables and fruit contain important quantities of simple sugars (lactose, fructose, glucose), so a significant intake of vegetables and a daily ration of milk easily lead to exceeding 10% of calories daily obtained from this type of sugar. But this, far from constituting risky behavior, is even desirable.

Some polysaccharides have a composition that cannot be degraded by amylases, so they are indigestible: they are dietary fiber, like cellulose, which is rich in vegetables. Although they cannot be used as sources of calories, these polysaccharides are very useful because they contribute to the formation of the faecal mass and because they provide nourishment to the intestinal bacterial flora. In a balanced diet, carbohydrates must supply about half of the daily calories. For a normal adult person with moderate physical activity, therefore, about 300-350 g of carbohydrates per day are needed. When physical activity increases, carbohydrate intake must also be increased; on the contrary, in case of slimming diets, their intake is reduced, as is that of lipids.

Carbohydrates, especially complex carbohydrates, are fermented to a small extent by the intestinal bacterial flora, with the production of gas. This phenomenon can be perceived as a nuisance and can lead to limit the intake of foods such as bread, pasta and legumes. In reality it is a completely physiological and useful event for the body: in fact, microorganisms such as lactobacilli and bifidobacteria feed on these sugars, which therefore play a prebiotic role, i.e. their presence contributes to preventing the proliferation of pathogenic bacteria and to strengthen the intestinal immune defenses.

When a person does not have a sufficient quantity of intestinal enzymes to digest particular sugars, manifestations of intolerance occur: very known, because rather widespread, it is lactose, a substance consisting of two sugars (glucose and galactose), which cannot be absorbed as such but must undergo degradation in the two constituent molecules by intestinal lactase. If this is deficient, as frequently occurs in adults, the ingestion of lactose-containing foods causes abdominal discomfort and diarrhea. The diagnosis of this type of intolerance is very simple, it is based on the patient's anamnesis and can be confirmed by the breath test, which measures the quantity of hydrogen produced by the intestinal flora contained in the exhaled air. starting from undigested lactose.

Go back to the menu


The main characteristic of fats is that they do not dissolve in water. Most of the lipids present in them are made up of triglycerides, substances formed from an alcohol, glycerol, combined with three molecules of fatty acids. Many of the physical, organoleptic and metabolic characteristics of lipids are due to the nature of the fatty acids that make them up. Lipids are the energy nutrients par excellence, in fact they bring 9 kilocalories per gram and should represent, in a balanced diet, about 30% of the daily calories consumed. They then perform some other functions, such as structural and regulatory, as they are part of cell membranes and are precursors of active molecules in numerous pathophysiological mechanisms. Foods composed almost exclusively of fats are oils (the only ones that take a liquid form at room temperature), margarines, butter, lard and lard. Cheeses, some cured meats, mayonnaise and many confectionery preparations contain high percentages. Due to the lipid content these are all particularly calorie foods.

The different chemical characteristics of fatty acids are the basis of the known distinction between saturated and unsaturated. This refers to the existence or not in the molecule of double bonds, that is a particular modality of union between two adjacent carbon atoms in the fatty acid chain; we therefore speak of:

  • saturated fatty acids if there are no double bonds;
  • monounsaturated fatty acids if there is only one double bond;
  • polyunsaturated fatty acids if there are two or more double bonds.

The higher the level of unsaturation, the more liquid tends to appear. An oil can be made solid by adding hydrogen to saturate the double bonds between the carbon atoms: thus, for example, margarines are obtained. In this process, some saturated bonds return spontaneously unsaturated, losing hydrogen but taking on a new and unnatural form, the trans form (the natural double bonds present a conformation called cis). Margarines, therefore, are hydrogenated fats which, unless special industrial measures are taken, contain trans fats, considered dangerous for health because they induce the increase in cholesterolemia. Saturated fats are found mainly in coconut and palm oils and in milk; these present molecules between 12 and 16 carbon atoms (lauric, myristic and palmitic acids) and can cause an increase in plasma cholesterol. Coconut oil, palm oil and hydrogenated fats are widely used as ingredients in industrial baked goods (crackers, biscuits, rusks, snacks, sweets) and in ice cream.

In the case of milk and dairy products, it should be remembered that any modest increase in cholesterolemia is largely offset by the effects of cardiovascular protection highlighted by these products. Even the meats, especially of bovine origin, contain saturated fats but with a slightly longer chain and made up of stearic acid (18 carbon atoms). The latter, once ingested, is partially transformed into its monounsaturated equivalent, oleic acid, and does not cause increases in cholesterolemia.

Unsaturated fats are present in vegetable oils. Monounsaturated oleic acid with 18 carbon atoms characterizes olive oil, which also contains numerous non-lipid substances. The whole gives this fat undisputed health properties, especially in the prevention of cardiovascular diseases. Seed oils contain polyunsaturated omega 6 class, the effects of which are controversial. In fact, their consumption favors a modest reduction of cholesterolemia but also the development of bile stones and inflammatory processes. The latter effect is explained by the fact that omega 6 fatty acids are the precursors of some molecules involved in the mechanisms of inflammation. The lipids contained in fish are rich in polyunsaturated fatty acids of the omega 3 series, to which they attribute important properties in the prevention of cardiovascular diseases. Food supplements and omega 3 fatty acid drugs are used effectively for the reduction of plasma triglycerides. For these properties it is recommended to consume at least 2 portions of fish per week.

However, it should be remembered that only fatty fish caught in the sea, such as the blue one, brings significant quantities of omega 3, while lean and farmed fish have small quantities. Fishery products, however, raise concerns due to marine pollution, sometimes responsible for the presence of dangerous pollutants such as mercury, dioxins and polychlorinated biphenyls, at levels above the safety threshold, particularly in large species.

Go back to the menu


Proteins are polymers made up of amino acids, which are the building blocks of our body and in fact represent the individual building blocks of biological structures.

Our body manages to produce only 12 of the 20 amino acids that are used for the synthesis of proteins: the other 8, called essential, must draw them from the outside. Since proteins are continuously degraded and their amino acids eliminated, it is necessary to replace the essential ones with the diet; for this reason they are considered plastic nutrients. Our protein requirement is just under 1 g per kilo of body weight. If larger quantities are taken, they are used to obtain energy or transformed into storage fat. Protein makes 4 kcal per gram.

Protein-rich foods are meats, fish, eggs, milk, cheeses. Plants contain less valuable proteins because they are low in essential amino acids. However legumes, especially soybeans, have good quality proteins, particularly rich in the amino acid lysine, while they lack sulfur amino acids (cysteine ​​and methionine). Cereals have poor quality proteins but are rich in sulfur amino acids. The combinations of legumes and cereals complement the respective deficiencies, giving rise to a complete set of amino acids. From this observation the concept of single dish was born, such as pasta and beans, where in a single gastronomic specialty the properties of an entire meal are found, with a decidedly lower overall number of calories.

Protein deficiency, an event unfortunately easily observable in Third World countries and in some categories of subjects also in the western world (for example the institutionalized elderly), has serious consequences. The most conspicuous aspects are the reduction of the immune defenses, which predisposes to infectious pathologies, and the decrease in the levels of circulating proteins in the plasma, which causes the appearance of edemas.

Excessive protein introduction can also have unwanted consequences. The issue is topical, as high-protein diets have become fashionable for some years. Our daily eating habits already lead us to take more proteins than necessary: ​​on average, an adult man ingests 80-90 g per day against the recommended 60-70 g.

Too many proteins excessively engage the kidneys in their work of purifying the body from nitrogenous substances originating from the metabolism of amino acids and this hyperactivity depletes the capacity of the kidney ahead of time, which works just like a filter, and therefore the more it works the more it clogs. The high-protein diet also increases the loss of calcium in the urine and acidifies the blood. These are phenomena destined to produce, over time, the depletion of the mineral component of the bone, up to the development of full-blown osteoporosis. Recently it has been observed that the intake of high quantities of proteins increases the presence of certain growth factors, substances produced by the body and capable of stimulating the development of different types of cells, including neoplastic ones. It is therefore not advisable to follow high protein diets, unless there are valid reasons and the positive opinion of a doctor.

Go back to the menu