Lipids are organic biomolecules generally formed by carbon and hydrogen and, to a lesser extent, also oxygen. However, sometimes they can also contain phosphorus, nitrogen and sulphur.
The world of lipids can be a confusing terrain, as the terms lipids, fats, fatty acids or triglycerides can be used interchangeably even though they do not mean the same thing. In this article we will focus on fats and their nutritional significance, so we will not go into detail about other important functions of lipids, such as: structural or transport function.
Simple and complex lipids
The group of lipids includes many organic compounds that basically share two essential characteristics: they are insoluble in water and are soluble in organic solvents. In the traditional way and usually distinguish between simple lipids (fatty acid esters with alchols) and complex lipids .
The most important simple lipids are triglycerides, which are usually called fats since they are stored in the adipose tissue and are the main constituents of vegetable oils and animal fats, and whose function is basically energetic, but also insulating. Triglycerides are largely composed of fatty acids, for example, palmitic acid. Complex lipids, on the other hand, often have structural and functional tasks.
The fact that the properties of all these substances are different means that their metabolism is also significantly different.
Functions of Lipids
In general, the functions of lipids are:
- Energetic : For each gram, lipids provide 9 Kcal. If fat intake exceeds daily requirements, they are stored directly in the adipose tissue in the form of triglycerides.
- Structural : Some lipids such as cholesterol are part of the cell membranes and are precursors of hormonal steroids, bile acids and vitamin D.
- Transport : Transport of fat-soluble vitamins (A,D,E, K and carotenoids).
- Increase palatability : Enrich the taste of food
In addition, lipids provide essential fatty acids for the body
Essential and non-essential fatty acids
Fatty acids, like amino acids, can be divided into essential and non-essential . The difference between them is that the essential ones must be eaten from the diet and the non-essential ones can be produced by the body. Although essentials are classified into families such as Omega-3 fatty acids, the best known are, for example, linoleic acid or alpha-linolenic acid.
- You can learn more about essential amino acids in our post: “The 20 types of proteins and their functions in the body”
Saturated, unsaturated or trans fats (or fatty acids)
Fatty acids, according to their chemical structure, can also be classified in different ways:
All foods containing fat are composed of different types of fat, but the amounts of each type usually differ depending on the food. For example, pork is rich in saturated fat, while almonds are rich in unsaturated fat (also known as healthy fat).
The fatty acids in these fats do not have double bonds in their chain and are generally solid at room temperature . The body cannot take full advantage of this type of fat, so it accumulates in the arteries in the long run, which can lead to serious health problems. That is why different organizations specialized in this subject warn that the consumption of this type of fat should be moderate.
Saturated fat increases cholesterol more than any other type of fat (except trans fat, which we will see later), therefore, excessive consumption can increase cholesterol biosynthesis and has a thrombogenic effect. It is found in foods of animal origin such as meat, sausages, milk and its derivatives (cheese, ice cream).
Unsaturated fats are known as healthy fats because they increase good cholesterol , stabilize the heart rate, relieve inflammation and also provide other beneficial functions for our body. This type of fat is predominantly found in vegetable and fish foods.
It is possible to distinguish two types:
- Monounsaturated fats : This type of fat is found, for example, in olive oil, and the best known monounsaturated fatty acid is oleic acid. They are normally liquid at room temperature and have a single double bond in their structure.
- Polyunsaturated : Found in foods of vegetable origin, fish and seafood. They have two or more double bonds in their structure and are essential. They are classified in groups such as Omega-6 (linoleic and arachidonic acid) or Omega-3 (linolenic, eicosapentaenoic or docosahexaenoic acid).
If saturated fats are harmful to the body in the long term, even worse are the trans fats (processed fats) found in hydrogenated oils and certain processed foods. Technological processes, such as hydrogenation, oil refining, etc., cause a chemical transformation into certain fatty acids, which makes them harmful to our body.
Health professionals have long warned that diets high in trans fats increase beta-amyloid in the brain, which is associated with Alzheimer’s disease. In addition, the journal Neurology published research that found this type of fat is associated with brain shrinkage and an increased risk of stroke.
Other fat classifications:
In addition to the above, fat can be classified differently:
According to their origin
Fat can also be classified depending on the source from which it is obtained and can be of vegetable or animal origin. Examples of animal fat are found in eggs or veal, while those of vegetable origin are, for example, found in nuts or olives.
According to their shape
Depending on their shape, they can be solid or liquid. Liquids are known as oils and solids are known as fats, simply. This difference can be seen with the naked eye, although it is true that the consistency of fats can vary and have a gelatinous texture reminiscent of liquids.
This classification of fats can be made at a glance .
According to your visibility
Finally, fat can be classified as either visible or invisible. Visible fat is, for example, that found in a piece of loin, so it can be removed and not consumed. Invisible fat, on the other hand, is, for example, the fat found in milk.
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