Lipids are more commonly known as “fats”, and are one of the three major types of macronutrients, i.e., one of the constituents of foods that contribute to energy intake (together with carbohydrates and proteins).
What are fats?
Fats play two major roles in the body:
- an energy storage role. In this case fats are in the form of triglycerides, and are particularly found in adipose tissue;
- a structural role. In this case, they are in the form of phospholipids and are the main constituents of cell membranes, ensuring their fluidity, in particular.
Triglycerides and phospholipids in the body consist mainly of fatty acids that are provided by the diet and, for some of them, synthesised by the body. Dietary fats are predominantly in the form of triglycerides.
In addition to their major role as a source of energy and as constituents of cell membrane lipids, the metabolic functions of fatty acids vary according to their nature: some are precursors of molecules that regulate a variety of physiological functions (platelet aggregation, inflammation, vasoconstriction, etc.); others can regulate gene expression, particularly of lipid metabolism, etc.
Cholesterol is also a type of fat. It is the precursor of steroid hormones (œstrogen, testosterone, etc.). It is also an important component of cell membranes, particularly in the brain. In the body, it comes either from food intake or from endogenous synthesis (i.e. by the body itself). Cholesterol synthesis and absorption are both carefully regulated, helping to ensure a stable level of cholesterol in the body. As with other fats, it is transported in the blood in the form of lipoproteins (very-low density lipoproteins [VLDL], low density lipoproteins [LDL] or high density lipoproteins [HDL]). An elevated plasma concentration of cholesterol is a risk factor for cardiovascular disease.
In the diet, cholesterol is contributed exclusively by products of animal origin. It is found in very low quantities in plants, in compounds that are similar to cholesterol, phytosterols.
Classification of fatty acids
Fatty acids can be classified in different ways. From a biochemical viewpoint, there are:
- saturated fatty acids(SFA), which have no double bond;
- monounsaturated fatty acids (MUFA), which have just one double bond;
- and polyunsaturated fatty acids (PUFA), which have several double bonds.
From a physiological viewpoint, there are: we distinguish between essential (which also include conditionally essential) and non-essential fatty acids.
- essential fatty acids are necessary for the development and proper functioning of the human body, and cannot be manufactured by the body;
- conditionally essential fatty acids are indispensable for normal growth and physiological functions of the cells, and can be manufactured from their precursor if it is provided by food. They are absolutely required if their essential precursor is absent;
- non-essential fatty acids.
There are two major types of essential fatty acids:
- omega 6 polyunsaturated fatty acids(or n-6 PUFAs), whose precursor and main representative is essential linoleic acid (LA). Its main derivative is conditionally essential arachidonic acid;
- omega 3 polyunsaturated fatty acids (or n-3 PUFAs), whose essential precursor is alpha-linolenic acid (ALA). From this fatty acid eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids can be synthesised. However, DHA, unlike EPA, cannot be synthesised in sufficient quantities to meet the body’s needs, even in the presence of ALA. DHA is therefore considered to be essential while EPA is considered to be conditionally essential.
The non-essential fatty acids include, in particular, oleic acid (the main monounsaturated fatty acid in our diet), and the saturated fatty acids (SFAs). Saturated fatty acids consist mainly of lauric, myristic and palmitic acids which, are atherogenic in excess . Other SFAs, particularly those with short and medium chains, do not have this effect and may even have positive effects on health.
Dietary fats can come from both products of animal origin (fish, eggs, cheeses, delicatessen meats, meat) and plant-based products (oil seeds and oleaginous fruits, oils). It is important to remember that processed products (croissant-like pastries, chocolate bars, etc.) contain a great deal of fat, even if this is not apparent.
> See the list of foods that are high in fats, saturated, monounsaturated or polyunsaturated fatty acids, and various single fatty acids can be accessed via the table Ciqual, by clicking on the “fat” icon.
2010, reassessed population reference intakes for fatty acids
Recent scientific data have helped refine the specific physiological and biochemical effects of fatty acids.
To establish PRIs, the The Agency took an innovative approach to determine the population reference intakes by considering both the physiological requirement for fats, corresponding to what the body needs to ensure proper functioning, but also the optimal physiological requirement, to prevent for primary prevention of certain diseases (metabolic syndrome, diabetes, obesity, cardiovascular diseases, cancer -– particularly breast and colon cancer -,– and other pathologiesdisorders such as age-related macular degeneration).
Recommendations on total fats
As with all nutrients, excessive consumption of fats can be harmful to health. The recommended share of fats in energy intake is 35 to 40%. This range covers requirements in essential fatty acids while taking into account disease prevention factors. into account. In France, the upper limit of this range is exceeded by around 43% of adults and 34% of children.
Attention should also be paid to the quality of the fatty acids provided by the diet, as they are not all equivalent. Thus, PRIs have been proposed for the essential fatty acids (LA, ALA, DHA), EPA, the three atherogenic saturated fatty acids that are atherogenic in case of excess, and oleic acid. A recommendation was also made for all saturated fatty acids, although they do not all have the same physiological effects.
These recommendations were made for adults and then separately for pregnant and breastfeeding women, and infants.
FattyPopulation reference intakes for fatty acids recommendations for in adults consuming 2000 kcal/day
The values are expressed, except for EPA and DHA, as a percentage of energy intake without alcohol, which is called “energy intake” (EI),) for simplicity. In the case of DHA and EPA, the values are expressed in milligrams, as the available studies have used this unit.
Docosahexaenoic acid, DHA
Eicosapentaenoic acid, EPA
Lauric + myristic + palmitic acids
≤ 8 %
Total saturated fatty acids
Population reference intakes for PUFAs in pregnant women consuming 2050 kcal and breastfeeding women consuming 2250 kcal/day
Population reference intakes for PUFAs in newborns/infants (first six6 months)
2,7 % EI
0,45 % EI
EPA < DHA
The values are expressed as % of energy intake (EI) or as a percentage of total fatty acids (TFA) for milk providing, for 100 mL reconstituted, 70 kcal and 3.4 g in total fats
 Refers to a substance that contributes to the deposition of high-cholesterol plaques on inner arterial walls.