In this section, we examine in greater detail the main nutrients present in plant foods, describing their functions.
There is also a shorter discussion available for each nutrient.
Carbohydrates are the major component of any balanced diet and are the primary source of ready energy, which means that the body works best when it can get its energy from this source, a bit like a car when filled with the right fuel. They are divided into simple carbohydrates (or just "sugars") and complex carbohydrates.
Complex carbohydrates are derived from the union of many molecules of simple carbohydrates. In this way, they lose the sweet taste, typical of sugars, but, above all, are absorbed much more slowly. They must be digested, i.e., broken down into sugars to be absorbed from the gut, then cross the wall and pass into the blood. This breaking-down takes time and the presence of fiber slows down the process even further. For this reason, the complex carbohydrates that derive from unrefined plant foods like whole grains and legumes are able to increase the blood sugar in a slow and stable manner, avoiding those peaks resulting from intake of simple sugars and which trigger the yoyo effect throughout the circuit responsible for the hyperinsulinemia and the need for the continuous intake of sweet foods.
Carbohydrates are present especially in the plant Kingdom; foods of animal origin contain only small amounts in the form of glycogen deposits in the muscle tissues or as lactose, the sugar of milk.
Regarding their volume, they supply few calories, so a feeling of satiety can be rapidly reached, which is useful when trying to avoid exceeding with the calories consumed. Carbohydrates can contribute up to 60-65% of the total calories of a balanced diet.
Proteins, often referred to as the "building blocks" of the body, have different functions: hormonal, immune response, structural, transportation. They consist of chains of simpler elements, amino acids, of which are of 20 different types. Of these 20, 8 are called "essential" because they must be introduced with the diet, our body is unable to "build” them from precursors. All 8 essential amino acids are well represented in the various plant foods.
The proteins in the diet are digested, that is broken-down in the individual amino acids that compose it, and become a part of the body's amino acid pool; from this come the amino acids necessary to synthesize new proteins needed for various functions. For protein synthesis to occur, it is necessary that the body have all of the 20 different amino acids in the right proportions. The pool of amino acids acts as a deposit: amino acids derived from various plant proteins are there available for the building of proteins that our body needs.
The animal foods contain all the essential amino acids in, or close to, the proportions laid out in the reference pattern; also plant foods contain all the essential amino acids, although they may contain one of them to a lesser extent than necessary (except some foods such as soy and pseudo-grains, which contain all the amino acids in the right proportion). The amino acid present in lower quantities is called a "limiting amino acid". This however is not a problem, because different foods have a different limiting amino acid, so a diet including different foods (not just grains, not just vegetables, not just nuts) provides all the necessary amino acids in the correct quantity, because all amino acids are conveyed in the above mentioned deposit and so it doesn't matter the proportion of amino acids of a single food.
Precisely thanks to the existence of the pool of amino acids, there is no need to combine different plant foods or pay particular attention: our body does the combining by taking what he needs from the pool.
The amount of protein needed for an adult is 0.9 grams per kg of body weight per day, equivalent to about 50-70 grams for a person of average weight and physical activity (vedi Tabella dei Livelli di Assunzione di Riferimento di Nutrienti sul sito SINU). This amount corresponds to about 10-15% of the total calories of the diet and this percentage is exactly the average of the plant foods, while animal foods greatly exceed it: this means that consuming animal foods always accordingly involves the intake of protein quantities significantly higher than necessary. This is a situation in itself harmful to the body, but above all, animal protein is always accompanied by harmful saturated fat and cholesterol, while vegetable proteins are associated with beneficial substances such as fiber and complex carbohydrates, and exert a protective effect against certain cancers, overweight-obesity and arteriosclerosis.
For this reason it is always best to get our protein needs from plants, and there is no need to count the proteins consumed to verify if “enough” has been eaten, because if the amount of calories in our diet satisfies our calorie needs, we "automatically" consume the amount of protein needed. In fact, with the exception of fruit, all plant foods (vegetables included) have a protein density greater than the 10% of energy from protein which is recommended in a balanced diet.
Fats (also known as lipids), are primarily of energy importance, but also have structural and regulatory roles within the organism. In the diet of an adult they should represent 20-35% of the total energy. They include polyunsaturated, monounsaturated, saturated fats, trans fats and hydrogenated fats.
The first subdivision is between "oils" and "solid fats". The oils remain liquid at room temperature: most vegetable fats are oils. Solid fats are the ones that remain solid at room temperature and are almost all animal in origin (butter). Just a few vegetable fats, the tropical oils (palm, coconut) and the trans are solid fats. Trans fats occur naturally only in animal foods, the latter of which contain about 20% of them, while for the most part they are produced by the food industry during the process of hydrogenation of vegetable fats, making them solid at room temperature (like margarines).
Cholesterol also belongs to the family of fats, and in the Western diet the average cholesterol intake is 400 mg per day. This fat, saturated and trans fats are the main determinants of blood cholesterol levels. Cholesterol is not an "essential" nutrient because the body is able to produce the necessary quantities to its needs (synthesis of hormones, bile production). Consuming it with the diet, therefore, means adding it to our body, with harmful effects.
Cholesterol is present only in animal foods, while other types of fat are found in both the animal and vegetable Kingdoms, but with a different distribution: animal foods are full of harmful saturated fats, while plant foods contain predominantly saturated fatty acids (monounsaturated and polyunsaturated), with the exception of tropical oils (palm, coconut).
A vegetarian diet promotes a healthy fat intake, that is of unsaturated fatty acids, in the correct amount, while, if it does not include processed products, it is naturally low in fats that are harmful.
In particular, the polyunsaturated fatty acids omega-3 and omega-6 family of fatty acids are considered "essential" because the body cannot produce them on its own. They are not used that much for energy purposes, but primarily for structural and regulatory purposes: in fact, they become part of nervous tissue and cell membranes, whose fluidity is in direct relation with the health of the cell itself, as well as in the formation of molecules to regulatory action, the eicosanoids.
The ideal ratio between omega-6 and omega-3 is 2.3:1 and should not exceed that of 4:1. Because the omega-6 is abundant in foods, it is necessary to consume preferred sources of omega-3 to meet this ideal proportion. In the "recommendations" section you can find out more about omega-3 and omega-6.
Dietary fiber consists of molecules (carbohydrates and others) indigestible by the human intestine and is present exclusively in foods of plant origin. Soluble fiber is found mainly in fruits, legumes and oats: it dissolves in fluids, forming a kind of gel that blends with the rest of the food present in the dish and in the digestive tract. Insoluble fiber on the other hand is formed mainly from cellulose and lignin, filaments contained in vegetables and in some fruits (for instance, persimmons) or that make up the outer shell of the grain (bran), legumes (the cuticle) and fruit (the skin).
Fiber helps reduce blood cholesterol levels and the risk of heart disease and certain types of cancer (colon, breast, prostate). It is crucial to the proper functioning of the intestines, helping to prevent diverticulosis and constipation. Fiber also helps to reach the feeling of satiety earlier, thus helping to control body weight.
Other useful fiber effects consist of: the shortening of exposure time of the cells of the intestinal mucosa to harmful substances carried by the food; in the creation by the soluble fiber, of a film lining the surface of the digestive tract; the protective effect of volatile fatty acids, produced by the bacteria that digest.
It is often argued that an excess of fiber in the diet may reduce the absorption of essential minerals for the body, such as iron, and may result in deficiency problems. In fact, this effect of fiber appears to be irrelevant, because the fiber-rich foods are also very rich in minerals.
It has been verified that, with increasing intake of fiber, it also increases the intake of minerals and that populations where the diet is predominantly plant-based, there are not any particular problems of deficiency. This negative effect exerted by the fiber on the absorption of minerals occurs only when the fiber is assumed artificially, so not through food, but for example from bran powder or supplements used by people who suffer from constipation, whose diet is based on animal foods instead of vegetables.
Only by consuming fiber as part of a complete plant food, is it possible for an adult to eat the the optimal amount (around 30-40 grams and more per day) with the certainty of consuming as well the recommended amounts of minerals (especially iron, calcium and zinc) and to exploit the favorable effects.
Regarding fiber, also read the special recommendations during weaning, because the consumption of fiber, unlike with the adult, in the infant should be kept very low. Children can consume integral foods only at the end of the second year of life.
Vitamins are essential to the body, since they are involved in many metabolic processes. With the exclusion of vitamin D, vitamins are nutrients defined as essential, as they must be introduced with the diet, and it is not possible for our bodies produce them from other substances.
Vitamins are, with certain exceptions, synthesized by microorganisms and plants. This means that all the vitamins that are obtained by the intake of animal foods are not produced by the animal, but are derived from its diet. The proportion of excess vitamins that is neither used nor eliminated is deposited in the tissues of the animal itself (or in its products, such as milk), which then in turn becomes the source, though neither essential nor irreplaceable. All the more so that currently it is common practice to feed farmed animals with feed artificially supplemented with various nutrients, including multivitamin preparations, then vitamins that are found eventually in animal products (meat, fish, dairy products and eggs) are often derived from these supplements. This is the case of the famous vitamin B12, for example.
The table Livelli di Assunzione di Riferimento delle vitamine sul sito SINU shows the daily intake levels for the main vitamins in the Italian population, broken down by gender and age groups.
Plant foods are good sources of all vitamins (except vitamin B12, discussed below) and they are also the exclusive source of vitamin C and beta carotene, important antioxidant vitamins. Vegetarians consume an average amount of vitamin C, folic acid and beta-carotene considerably higher than that of omnivores: as substances with a protective effect, consuming somewhat higher levels with the diet can only have positive effects on health.
Here is a list of the major vitamins.
Beta carotene (vitamin A) is involved in the health of skin, mucous membranes and the eye, and is a powerful antioxidant that helps prevent certain cancers, and fights infections.
B vitamins (thiamine, riboflavin, niacin, pyridoxine and folic acid) are important for energetic metabolic processes, the nervous system and the formation of tissues; folic acid promotes the production of red blood cells. The consumption of high amounts of folic acid (from plant foods and supplements) is recommended for women who are pregnant or are planning becoming pregnant, to prevent the development of spina bifida and other neural tube defects, and anencephaly in the fetus.
For folic acid you are invited to read the particular recommendations in pregnancy valid for all pregnant women.
Vitamin B12 presides over cell replication and the integrity of the peripheral and central nervous systems. Read on the page of "recommendations" how to get vitamin B12.
Vitamin C is involved in wound healing, in the health of teeth and joints, and is an antioxidant that also benefits non-heme iron absorption.
Vitamin D regulates calcium-phosphorus metabolism and is formed by the action of sunlight (UV radiation) on the skin. Only 10% maximum is obtained from diet, and then only from non-vegan diets. Read on the page of "recommendations" how to get vitamin D and how it is associated with calcium metabolism.
Vitamin E is a powerful antioxidant: it protects the tissues and other nutrients such as beta-carotene and essential fatty acids from oxidation.
Vitamin K intervenes in the coagulation process and is important for bone health.
The minerali are essential nutrients which perform multiple functions within the body (structural, biochemical), some of which are not yet fully known.
Some minerals are present in the body in relatively large amounts (calcium, phosphorus, magnesium, potassium and sodium), while others are present in very small quantities or traces (chromium, iron, fluorine, iodine, manganese, copper, selenium and zinc).
The table of Livelli di Assunzione di Riferimento dei minerali sul sito SINU shows the daily intake levels for the main minerals in the Italian population, broken down by gender and age groups.
The amount of minerals provided by natural plant foods is more than adequate: their bioavailability, i.e. the quantity actually usable by the body with respect to that introduced, depends on many factors. Some preparation techniques, like soaking legumes and whole grains, leavening, fermentation and germination, are able to increase the absorption of certain minerals. The simultaneous presence in the meal or the foods of some organic acids (such as phytate and oxalate/ascorbic acid), or the composition of amino acids of proteins in foods consumed may have opposite effects on bioavailability.
It should be remembered, however, that the body is able to regulate itself autonomously in relation to its needs: this is called homeostatic regulation. This ability allows it to increase its capacity of mineral absorption and reduce losses in the presence of reduced dietary intake and/or increased requirements.
Let’s review the more important minerals.
Calcium is a mineral necessary for the formation of teeth and the skeleton, involved in the clotting process, in muscle contraction and nerve conduction. The calcium in foods helps to maintain bone mass, but it is controversial today to what extent the amounts consumed help reduce the risk of osteoporosis.
Calcium is continuously excreted via urine, feces and sweat, and these losses are compensated, if necessary, through an increase in the absorption and reduction of losses. In adults up to 30 years or so, the losses are generally lower than the amount consumed. After this age, the body loses more calcium than it can store and the bones begin to lose more calcium than they can fix. When too much calcium is lost, the bones become brittle (osteoporotic). The rate at which calcium is lost depends on certain lifestyle habits, in particular:
Diets rich in protein increase the loss of calcium in the urine. Animal proteins are responsible for greater calcium losses than plant proteins because they are rich in sulfur amino acids that affect renal acid load. However, recent studies seem to suggest that this phenomenon may not be able to negatively affect bone health. Therefore:
Read on the page of "recommendations" how to get calcium from the diet and what are the foods rich in calcium.
Iron is essential for the transport of oxygen by red blood cells and muscle formation. Iron deficiency anemia is the most common anemia disease in the world, and has the same prevalence in omnivores and vegetarians, especially in women of childbearing age and in athletes.
The vegan diet is the richest in iron, richer than that of lacto-ovo vegetarians, and that of omnivores.
Food iron is present in two forms: heme iron, more easily absorbed; non-heme iron, which is much more sensitive to substances and practices that inhibit absorption (tea, infusions, coffee, cocoa, spices, fiber, calcium from dairy, phytates) and those that facilitate it (vitamin C and other organic acids present in fruits and vegetables, leavening, germination and fermentation, soaking, cooking). The non-heme iron is the totality of iron contained in plant foods, but also constitutes 60% of iron content in meat (and this means that only 40% of the iron in meat is heme iron, not its entirety, contrary to what many believe).
The assimilation of iron from food varies, ranging from 2-20% for non-heme iron, to about 20% for heme iron, but the situations that enhance the absorption of plant-origin iron (see above) are largely a part of the diet and also allow for the absorption of non-heme iron as well, in amounts similar to that of heme iron, i.e., around 20%: this means that the iron requirement of vegetarians could be considered almost comparable to that of non- vegetarians. But, since at the same time a 100% vegetable diet is richer in iron than the omnivorous diet, it is clear that there cannot be increased risks of iron deficiency, rather, far from it.
Usually vegetarian adults have blood levels of ferritin (which is the laboratory test indicating the content of the organism’s deposit iron) within the normal range, but with lower values compared to non-vegetarians, which is protective for our health, because high iron stores are a risk factor for chronic diseases.
Therefore any additional practices that maximize the absorption of non-heme iron (for example the addition of vitamin C-rich foods to the meal, such as lemon juice in the water or orange juice ) should be applied only when there is real need , not as usual practice, otherwise the iron deposits increase, which promote the oxidative damage of molecules and cells of the organism.
Finally, the non-heme iron is preferable to heme because the latter seems to favor the malignant cell transformation of intestinal cells and could be one of the factors responsible for the relationship between meat intake and increased risk of colorectal cancer.
Below is a table showing the iron content of plant foods and, for comparison, that of some meats (source: elaborated from INRAN data, 2000).
|Food||Iron (mg per 100g, edible part)|
|Borlotti beans, black-eyed peas, cannellini beans, and lentils.||9.0-8.0|
|Green radicchio, pistachios||7.8-7.3|
|Soybeans, chickpeas, dried peaches, cashews||6.9-6.0|
|Muesli, lupines, dried apricots, arugula, broad beans, dark chocolate||5.6-5.0|
|Peas, oat flour, buckwheat||4.5-4.0|
|Dried plums, toast, durum wheat||3.9-3.6|
|Olives, roasted peanuts, dehydrated peaches, millet, common wheat, hazelnuts, and raisins||3.5-3.3|
|Whole wheat flour, almonds, dried figs, parboiled rice, spinach||3.0-2.9|
|Deer and guinea fowl||2.8|
|Dates, walnuts, whole wheat bread, corn||2.7-2.4|
|Young beef, pork, turkey, chicken||1.9-1.6|
Iodine is essential for the correct functioning of the thyroid gland. The recommendations for the general population, and thus, vegetarians included, indicate to consume iodized salt (only 1 teaspoon per day is necessary). Even algae are rich in iodine, but their iodine content varies greatly depending on the type of alga and on where it comes from and the lot, so it's not easy to take the right amount of iodine from algae, the use of iodized salt is much easier. If you consume algae, it is advisable to vary the alga and eating them on the whole 3-4 times a week using them to cook legumes (Kombu algae) and soups (Wakame algae) and to flavor grains, vegetables and soups (all others).
For iodine, please read the special recommendations during pregnancy.
Magnesium is a mineral that enters the skeleton’s structure and is involved in muscle energy metabolism; selenium is a mineral which is beneficial to the immune system for its antioxidant action; potassium is used to maintain normal blood pressure and to help reduce it in sufferers of hypertension and to promote greater bone mineral content; zinc is an important mineral for the immune system, skin integrity and is used in many metabolic reactions; for zinc, as with other minerals, self-regulation mechanisms develop which allow, in very low dietary intakes and/or increased demands to increase the absorption and reduce losses of the mineral.
These are naturally occurring chemicals in plants, which give color, flavor, aroma and structure, which have developed over thousands of years of evolution to defend the plant from the effect of free radicals, from attack by viruses, bacteria and fungi and damage to components of the cell, in particular DNA. The more the plant develops and grows in adverse natural conditions, the greater its content of phytocompounds.
In humans the phytochemicals have no functions strictly "nutrients", but are just the same important, as they are responsible for many beneficial effects on health: contributing to inactivation of substances that turn normal cells into cancer cells, suppressing the growth of malignant cancer cells and counteracting arteriosclerosis.
There are thousands of these substances , many yet to be discovered, and act differently and synergy, exercising overall protective effects against infections, tumors, diabetes, hypertension and cardiovascular disease, and cerebrovascular disease.
Only plant foods unprocessed by the food industry and not preserved (as for example the fresh vegetables in plastic envelopes with a protected atmosphere), contain the phytocompounds. Particularly rich are grains, legumes, vegetables and fresh fruit and spices.
It needs to be pointed out that many studies have confirmed the absolute ineffectiveness and the potential danger of taking these substances indiscriminately in the form of supplements. The consumption of high doses of antioxidants, as well as it is possible to realize only through artificial products, can in fact interfere with the intake or the action of other nutrients, or cause the conversion of these substances with a protective action against free radicals into pro-oxidant substances, i.e., with harmful effects.
It is, in fact, the entire range of these compounds, not taken as pills, but directly from the foods that contain them naturally, natural plant foods, which act as a team organized and able to protect the body from disease.
The texts on this page are partially drawn from the book "Il PiattoVeg, la nuova dieta vegetariana degli italiani", by Dr. Luciana Baroni, Edizioni Sonda 2015.