Late September 2026: in Year 1 of the food and wine services and hospitality track (the Italian alberghiero, the hotel and catering school), the subject — normally “Food science” (Scienza degli alimenti), but the name varies from school to school, so check your planner — has started with nutrients, together with the first notions of HACCP (the food safety system) and the first hours of kitchen or dining-room lab. The first test falls four to seven weeks later, so between the end of October and the start of November: frequent tests and oral assessments are the norm in this track, more than a single paper every two months.
It is worth saying straight away, because it changes the way you study from here on: the first and second years of vocational schools are the point where the risk of losing ground along the way is higher than in the whole of high school. It is not a judgement on the subject or the class — it is a structural fact of the move from middle school to a technical-practical track with a two-term timetable and the mid-year report already at the end of January. One more reason not to arrive at the first test improvising.
Food, nutrient, nutritional principle: three words that seem like synonyms
The first block of confusion starts here, and it is also the first question any teacher can ask aloud to see whether you have understood the logic before going into the details.
- Food (alimento): the thing you eat — an apple, a steak, a plate of pasta.
- Nutrient (nutriente): every chemical substance useful to the body contained in a food — the water in the apple, the proteins in the steak, the starch in the pasta.
- Nutritional principle (principio nutritivo): the same concept as nutrient, but grouped by category — carbohydrates, proteins, lipids, vitamins, mineral salts and water are the six categories of nutritional principles into which all nutrients are divided.
In practice: a food contains several nutrients, and each nutrient belongs to a nutritional principle. An apple is not a nutritional principle, it is a food that contains water, sugars (carbohydrates) and small amounts of vitamins and mineral salts.
The three functions: what each nutritional principle is for
Each nutritional principle performs one or more of three functions. It is the scheme you will use to answer any question of the kind “what are carbohydrates for” or “what are proteins for”: first the function, then the example, never the other way round.
| Function | What it does | Nutritional principles involved |
|---|---|---|
| Energy | Supplies energy to move, breathe, maintain body temperature | Carbohydrates, lipids, partly proteins |
| Building (or structural) | Builds and repairs the body’s tissues | Proteins, mineral salts (e.g. calcium in bones), water |
| Regulating (or protective) | Regulates the body’s chemical processes and protects it | Vitamins, mineral salts, water |
Note that some nutritional principles appear in more than one row: water, for example, has both a building function (it is part of the structure of every cell) and a regulating function (it regulates body temperature and the transport of substances). It is not a mistake in the table: it is the reason water is considered a nutritional principle in every respect, even though it supplies no energy.
Carbohydrates
Carbohydrates (or glucides) are the body’s most immediate source of energy. They are divided by complexity:
- Monosaccharides: the simplest form, a single unit — glucose, fructose (from fruit).
- Disaccharides: two monosaccharides joined — sucrose (table sugar, glucose + fructose), lactose (from milk).
- Polysaccharides: long chains of monosaccharides — starch (in pasta, bread, potatoes: the plants’ energy reserve) and fibre (in vegetables, fruit, wholegrain cereals: it is not digested, but it regulates the gut and is still a carbohydrate).
The reason pasta “gives energy” in a practical, concrete way for a chef: starch is a polysaccharide that the body breaks down into glucose during digestion, and glucose is the molecule cells burn to produce energy. A plate of pasta before a long service in the dining room is not a commonplace: it is the energy function of carbohydrates applied to a real case.
Lipids
Lipids (fats) are the most concentrated energy reserve among the nutritional principles — weight for weight, they release more than double that of carbohydrates and proteins (the exact figure is below). They are distinguished by the type of chemical bond:
- Saturated fats: single bonds between carbon atoms, typically solid at room temperature — butter, lard, the fat in meat.
- Unsaturated fats: they have one or more double bonds, typically liquid at room temperature — olive oil, seed oil.
Triglycerides are the form in which fats are stored and transported in the body, and are the most common type of lipid in foods. Cholesterol is a lipid different from triglycerides, present only in foods of animal origin, with a structural role in cell membranes: at this stage of the syllabus it is enough to be able to tell it apart from triglycerides, nothing more is needed.
Why oil is used for frying and not, for example, water: lipids withstand much higher temperatures before breaking down, and the high temperature of hot oil is what browns the surface of the food (the crispy crust) — a phenomenon you observe in the kitchen every day and which is, at bottom, a matter of nutritional principles and their physical and chemical properties.
Proteins
Proteins are chains of amino acids. The human body uses twenty different types; of these, some the body cannot produce on its own and has to take in with food — they are called essential amino acids.
The biological value of a protein measures how closely its composition in essential amino acids resembles what the human body needs: animal proteins (meat, fish, eggs, milk) generally have a higher biological value than plant ones (legumes, cereals), although by combining different plant foods in the same meal you can obtain a complete profile — a principle that will also come in useful when talking about menus and specific dietary needs later in the course.
The main function of proteins is building: they build and repair muscles, skin, hair, nails. Only in particular conditions (prolonged fasting, extreme effort) does the body also use them as a source of energy, but it is not their primary function.
Vitamins and mineral salts
Vitamins are divided into two groups according to what they dissolve in:
- Water-soluble: they dissolve in water (vitamin C, B vitamins). The body doesn’t store them for long, so they must be taken in regularly.
- Fat-soluble: they dissolve in fats (vitamins A, D, E, K). The body can accumulate them in fatty tissue, so a prolonged excess can be as much of a problem as a deficiency.
The most relevant mineral salts in the basic syllabus are calcium (Ca, building function: bones and teeth), iron (Fe, a component of haemoglobin, which carries oxygen in the blood) and sodium (Na, which regulates the balance of body fluids — and is also the reason table salt, sodium chloride, has to be measured carefully in a preparation).
Water
Water is the nutritional principle present in the greatest quantity in the human body. It supplies no energy, but it is indispensable for transporting substances, for the body’s chemical reactions and for regulating body temperature — which is why it is classified fully among the nutritional principles, even without energy value.
Energy value: how many kcal per gram
This is the number that appears on every food label and in almost every test on the subject, so it is worth learning well:
| Nutritional principle | kcal per gram |
|---|---|
| Carbohydrates | 4 |
| Proteins | 4 |
| Lipids | 9 |
| Alcohol | 7 |
Alcohol is not a nutritional principle (it builds and repairs nothing, it is not indispensable), but it supplies energy, so its value still appears in the total kcal calculation of a drink or a dish that contains it.
A calculation exercise from the label
Example label (made up, but with realistic values, like that on a packet of durum wheat pasta) — values per 100 g of product: 71.0 g of carbohydrates, 12.5 g of proteins, 1.5 g of lipids.
If the portion to cook is 80 g instead of 100 g, everything scales in proportion:
A frequent mistake in this type of exercise: adding up the grams of carbohydrates, proteins and lipids as if they were already energy — 71 + 12.5 + 1.5 is not a number that makes sense, the unit is wrong (they are grams, not kcal). You must always first multiply each nutritional principle by its own energy value, and only then add up the results.
More exercises in the test format
Classification by prevailing principle. For each food, state the prevailing nutritional principle: olive oil → lipids; chicken breast → proteins; bread → carbohydrates; orange → vitamins (in particular vitamin C) and water; milk → proteins and calcium.
Open question — “What are proteins for?” Model answer: Proteins have mainly a building function: they are made of amino acids and serve to build and repair the body’s tissues — muscles, skin, hair, nails. Some amino acids, called essential, the body cannot produce on its own and has to take in through diet. Only in particular conditions, such as prolonged fasting, are proteins also used as a source of energy, but it is not their primary function. Note the pattern: function, then mechanism (the essential amino acids), then the exception — it is the level of detail that an open answer worth a mark or two requires.
True or false.
- Lipids supply more energy per gram than carbohydrates. True (9 kcal/g against 4 kcal/g).
- Fibre is a type of protein. False: it is a polysaccharide, so a carbohydrate.
- Fat-soluble vitamins accumulate in the body more easily than water-soluble ones. True: they dissolve in fats and fatty tissue holds on to them.
- Water is an energy-providing nutritional principle. False: it supplies no kcal, but it still has a building and regulating function.
A necessary note, given the subject: this is a school syllabus on food science, not dietary advice or a diet — that is a different subject and not what I cover in a post preparing for a test.
How to tell if you are ready
Before the test, try answering these three questions without looking at your notes: what are the six categories of nutritional principles? Which function (energy, building, regulating) does each perform, and which nutritional principles cover it? How many kcal per gram do carbohydrates, proteins and lipids have? If you answer all three without hesitating, the rest — the examples, the classification of foods — comes almost by itself, because it rests on this structure.
Where to find more
If you want to review biomolecules from the general biology side (carbohydrates, lipids, proteins seen as components of the cell, not as nutritional principles), there is the post on biomolecules and the cell in Year 2 at technical institute — the angle is different, but the names of the substances are the same. If instead the first low grade of the year has already arrived, I wrote a guide for parents on what to do after the first failing grade in October. Later on, for food storage and safety, the post is HACCP and food contamination: a guide to the test.
For food science we don’t yet have a dedicated practice test on the site; you can still see the school practice tests to get an idea of the format we use for other subjects. For the rest of the science syllabus, the reference page is sciences; if you want a hand setting this chapter up properly before the test, start from the contact page — the first introductory call is free.
