Fats, also called lipids (from the Greek "lipos" = fat) are substances found mainly in foods of animal origin, but are also abundantly present in the vegetable kingdom. A fundamental characteristic of fats is that they are insoluble in water (they are defined hydrophobic) and for this they are clearly distinguished from proteins and carbohydrates.
Lipids perform very important functions. In fact, they have a role:
- energetic, are an "important energy reserve for the body; their composition makes them much more energetic than carbohydrates and proteins, in fact 1 gram of fat provides about 9 kilocalories (kcal)
- structural, they are fundamental components of cell membranes in all tissues
- functional and regulatory, are essential to the cell for its normal functioning and are precursors of many substances that perform a regulatory function in different systems of the body
Based on their chemical structure, lipids can be classified into:
- simple, formed exclusively of lipid molecules. They include glyceric, waxes, terpenes, steroids
- complex, in addition to a lipid part, they contain another of a different nature (phosphoric acid, carbohydrates, proteins, etc.). This group includes: phospholipids, glycolipids, lipoproteins
- derivatives, when they derive from the transformation of simple or compound lipids, such as cholesterol and vitamin D
The lipids of major nutritional interest are cholesterol and glycerides.
The cholesterol performs various biological functions in the body: it is a component of cell membranes, important for their fluidity and permeability and is also a precursor of vitamin D, of both male and female steroid hormones (testosterone, progesterone, estradiol, cortisol, etc.) and of bile salts and is therefore involved in the digestion of fats.
A distinction can be made between exogenous cholesterol, the one introduced with the power supply, and endogenous cholesterol (the largest percentage) that produced by the liver; both forms circulate in the organism.
Blood cholesterol is carried by lipoproteins LDL (from English "Low density lipoprotein") and HDL (from "English"high density lipoprotein"). LDL cholesterol is known as bad cholesterol because it can be transferred from the liver to the artery wall, thus contributing to the formation of plaques that clog the arteries.
HDL cholesterol, on the other hand, is known as good cholesterol because it represents the amount of cholesterol that is transported from the arteries to the liver where it will partly be transformed into bile salts.
Cholesterol plays an important role for the body, but when it circulates in the blood in too high quantities (above 200 milligrams per deciliter of blood) it becomes an enemy of health, especially when the quantity of LDL cholesterol increases. the “bad.” Generally, the “good” cholesterol (HDL) should never be less than 30% of the total cholesterol (LDL + HDL).
THE glycerides can be formed by the union of a molecule of glycerol (an alcohol) with one, two or three chains of fatty acids, respectively forming mono, from And tri-glycerides. They are abundantly present in the human body, since they represent the storage form accumulated in the adipose tissue and constitute about 96-97% of dietary fats.
The fatty acids that make up the glycerides, in turn, can be classified into:
- saturated fatty acids, mainly contained in foods of animal origin
- unsaturated fatty acids, (monounsaturated if there is only one double bond, polyunsaturated if the double bonds are more than one), present in a higher percentage in foods of plant origin
Based on their origin, fats behave differently: fats of vegetable origin are generally liquid at room temperature, while those of animal origin are solid.
To prevent possible damage and protect health, it is essential to control the quantity and quality of fat consumed and the total calories of the diet. In fact, the fats of foods ad high content of saturated fatty acids tend to raise the level of cholesterol in the blood even more than the dietary intake of cholesterol itself. On the contrary, the fats of foods high content of unsaturated fatty acids they do not raise the level of cholesterol in the blood but have a "protective action on cardiovascular health."Nutritional indications
According to the guidelines for proper nutrition, 20-35% of daily calories should come from fat, of which no more than 10% from saturated fat. In fact, it has been shown that higher intakes of saturated fat can lead to an increase in blood cholesterol levels, increasing the risk of cardiovascular disease. Exceeding the amount of fat, outside the recommendations provided by the guidelines, also means exceeding the calories.
If the calories introduced in the diet are greater than those required by the body, everything that the body finds in excess, because it is not used by the cells, is converted into body fat. Fats have a great energy power, they are able to provide 9 kilograms of calories for each gram Therefore, it is important to be careful not to overdo it because the risk of exceeding the caloric requirement is greater.
However, having a good intake of fats in the diet is of fundamental importance for the functions they perform and because, without them, it would not be possible to absorb some fat-soluble vitamins, such as A, D and E, and to introduce some essential fatty acids. such as those of the omega-3 and omega-6 series that cannot be produced by the body and must, therefore, be introduced through the diet. The fat-soluble vitamins, in fact, are a group of vitamins that are able to dissolve in fatty substances and therefore need a lipid percentage to be transported.
Most of the fatty acids can be produced by the body. However, humans do not have the enzymes necessary to produce two fatty acids, called "essential fatty acids", which must be introduced in the diet:
- omega-6 linoleic acid (LA, 18: 2 ω-6)
- omega-3 α-linolenic acid (ALA, 18: 3 ω-3)
From essential fatty acids the human body, through transformation processes (metabolic), is able to obtain others such as, for example, alpha-linoleic acid (GALA 20: 3 ω-6) and arachidonic acid (AA 20: 4 ω-6) starting from omega-6 linoleic acid (LA), while eicosapentaenoic acid (EPA, 20: 5 ω-3) and docosahexaenoic acid (DHA, 22: 6 ω-3) are synthesized from "ALA.
However, since the body's production of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is not always sufficient to meet the daily requirement, these fatty acids must be introduced in the diet and are also defined as essential. EPA and DHA are the most important long-chain fatty acids of the omega-3 (ω-3) series and carry out structural and functional functions in the human body. Their intake should be about 250 milligrams per day.
Both omega-3 (ω-3) and omega-6 (ω-6) fatty acids are important components of cell membranes and precursors of many other substances in the body such as, for example, those involved in the regulation of blood pressure and in inflammation. Although both play a very important role, ω-3 and ω-6 are known to have "anti-inflammatory and pro-inflammatory activity, respectively; for this reason it is good that they are balanced within a diet.
The recommended optimal ω-6 / ω-3 ratio (LARN) is 5: 1, well below that currently estimated in Western populations which reaches 10: 1.Food sources of fat
Food sources of fat
Lipids are present in most food groups and foods that contain them generally provide a range of different fatty acids, both saturated and unsaturated. In Europe, the main dietary sources of unsaturated fatty acids include meat and derivatives, grains and derivatives, potatoes and salty snacks, mainly due to the vegetable oils used in the processing.
The lipid content in foods varies from very low levels in most fruits and vegetables, white meat and lean fish, to high levels in cheeses, red and processed meat and nuts. Foods richest in lipids are seasoning fats:
- saturated and monounsaturated fatty acids, the former are mostly present in butter (49 grams per 100 grams), palm oil (47 g / 100 g) and cheeses (15-20 g / 100 g). Monounsaturated fatty acids, on the other hand, prevail in "olive oil (72 g / 100 g)
- omega-6 polyunsaturated fatty acids (ω-6), the foods richest in linoleic acid are vegetable oils and fats: grapeseed oil (68 grams per 100 grams), soybean oil (51 g / 100 g), sunflower oil (50 g / 100 g). Animal fats are less rich in ω-6, while dried fruit contains 5-32 g / 100 g. Arachidonic acid is instead present in lard (2 g 100 g), in chicken egg yolk (0.7 g / 100 g), in poultry (0.6 g / 100 g). The quantity present in the fish depends on the species and, for the same species, on the age of the animal, the origin and the farming techniques. Wild fish contains less than farmed fish
- omega-3 polyunsaturated fatty acids (ω-3), foods with the highest content of linolenic acid are flax seeds (17g per 100g), soybean oil (8g / 100g) and nuts (6g / 100g). EPA and DHA are abundant in fish, especially those with fatty meats that live in cold waters (salmon). Oily fish (mackerel, herring, sardines) and wild fish that feed on phytoplankton, rich in EPA and DHA, also accumulate more ω-3 in their meats The absolute richest food in ω-3 is cod liver oil
- cholesterol, all foods of animal origin contain cholesterol; some such as kidney, egg and shrimp have a higher content. However, the cholesterol found in food has a rather low effect on the level of cholesterol in the blood (cholesterol) compared to that of saturated fats in the diet.
Indications and warnings
We often hear of the need to resort to the use of food supplements to increase the nutritional intake of one or more essential fatty acids: alpha linolenic (ALA), eicosapentaenoic (EPA) and docosahexaenoic (DHA).
The use of supplements (supplementation) would be aimed at increasing the protective role of omega-3s on cardiovascular health. It should be noted, however, that the scientific literature, to date, has reduced their actual need. Obviously, the data collected is refer to the use of omega-3 supplements and do not deny that eating fish rich in omega-3 is good for the heart. Omega-3s are essential for the proper functioning of cells and for the well-being of the whole body. Their intake through the choice of foods that contain them is essential. However, the prevention of cardiovascular risk and coronary heart disease through diet cannot be limited to the consumption of a single food or active ingredient, but to the consumption of a healthy and balanced diet that allows for the introduction of all the nutrients necessary for the body. without the need to resort to external supplements (read the Bufala).In-depth link
Italian Society of Human Nutrition (SINU). LARN 2014: Reference levels of nutrient and energy intake for the Italian population. Quantitative portion standards
Mayo Clinic. Dietary fats: how to make healthy choices (English)