Dietary fats are usually classified according to their chemical composition. Almost all the lipids in our diet or adipocytes are triglycerides made of a glycerol molecule linked with three fatty acids in an ‘E’-shaped structure (hence their name). As for the fatty acids, they combine oxygen atoms, a chain of carbon atoms of variable length and hydrogen atoms (two maximum). They may be regrouped in three main categories: saturated fatty acids, monounsaturated fatty acids and polyunsaturated fatty acids.
The various dietary fats
– Saturated fatty acids
They prevail in most animal fats (lard, butter), and also in some vegetable ones such as palm oil, which contains 50% saturated fatty acids (as opposed to 30% in butter), or coconut oil.
– Monounsaturated fatty acids
They prevail in olive, rapeseed and canola oils, therefore called ‘oleic oils.’
– Polyunsaturated fatty acids
Unlike their monounsaturated “cousins”, they display double links between their carbon atoms. They compound two main subgroups called omega-6 and omega-3.
• Omega- 6 prevail in the ‘linoleic’ oils: corn oil, sunflower oil or soy oil, and also in the meat and dairy from animals fed soy and corn cakes, i.e. most cattle and poultry.
• Omega-3 are mostly found in fish oils, as ecosapentaenoic acid (EPA) or docosahexaenoic acid (DHA), and in walnut, rapeseed, canola and linseed oils, as alpha-linolenic acid (ALA), as well as in meat and dairy from grass-fed animal, i.e. mainly sheep and goats (as long as these species keep being traditionally husbanded).
– Trans fatty acids
In order to round up this survey of the fats in our diet, let us finish with the trans fatty acids, usually created as a result of an industrial transformation process during which an unsaturated fat is ‘hydrogenated’ through being heated at 200 degrees and injected with hydrogen, so as to make it solid and stable. Hydrogenated oils and margarines have a much longer shelf life, which explains why the food industry appreciates them so much.
Fats and the human organism
Lipids are necessary to our health as they contribute to the formation of cell membranes and to hormone synthesis. They provide energy in a concentrated form: 9 kilocalories per gram of lipids, twice the yield of carbohydrates or protein, and they convey the indispensable liposoluble vitamins (A, D, E and K). They also provide us with essential fatty acids, which our body need and is unable to synthesize.
That said, lipids should never represent more than 30% of our daily caloric intake: a little butter at breakfast plus 2 to 3 tablespoons of added fats (less if one also eats oleaginous grains or fruits like almonds or olives). Any further intake is too much and as such potentially harmful.
– On a cardiovascular level
A moderate decrease of the fat content of our diet, along with a relative diminishing of the amount of saturated fatty acids and trans fatty acids (which both tend to increase the total cholesterol level and the percentage of “bad” LDL-cholesterol) and a relative augmentation of the intake of monounsaturated fatty acids (which improve the HDL-cholesterol/LDL-cholesterol ratio and prevent the aggregation of blood platelets, thus increasing the blood viscosity) and polyunsaturated fatty acids (which tend to decrease the total cholesterol level without impacting the HDL-cholesterol/LDL-cholesterol ratio), allows for a significant decrease of the coronary disease hazard. As for artificial trans-fatty acids, although their chemical structure remains unsaturated, they behave towards the organism as saturated fatty acids.
– On a metabolic level
The scientific community generally agrees that a correlation exists between the development the overweight and obesity, prediabetes and type 2 diabetes pandemic, and the changes in our diet, and more specifically with our eating less omega-3 fatty acids.
As a reminder, the ideal distribution of the various fatty acids in our diet should abide with the following guidelines:
– as few artificial trans-fatty acids as possible;
– about 50% monounsaturated fatty acids;
– 12% (at most) saturated fatty acids;
– and 30% polyunsaturated fatty acids, with a 4/5 omega-6 to 1/5 omega-3 ratio.
In modern Western diets, the ratio of the two latter categories more often verges on 1 to 20 (and up – or down – to 1 to 48 in the United States). It also has risen by 300% within the four last decades…