In foods, the main type of fat are called triglycerides, and each of them contains three different fatty acids. Fatty acids are chains of carbon atoms and have variable lengths (long, medium or short chain). Depending on their chemical structure, fatty acids are called saturated or unsaturated, the latter are divided into mono and polyunsaturated.
Fatty acids are a big source of energy for our bodies: from just 1 g of fat we are able to obtain 9 kcal, more than double compared to carbohydrates and proteins. But the reason why we have to introduce fats with food is not just so we can obtain energy: fats also have a structural purpose.
Triglycerides make up subcutaneous adipose tissue. In the right quantity, this is very important for several reasons: it covers us and protects us from traumas and heat dispersion as if it were a foam rubber suit; it serves as an energy reserve if we need it; it produces hormones and signals that regulate some of our functions such as, for example, hunger and satiety.
Fatty acids are also make up the membranes that surround all cells and all the organelles they contain. The type of fatty acid does have a difference in terms of its structural purpose: the saturated fatty acids stiffen the membrane, the unsaturated ones make it more fluid. The type of fatty acids that form a membrane determines its functionality, and therefore also the functionality of the cell. The type of fatty acids that make up our membranes depends largely on the fatty acids that we consume with our food.
Furthermore, highly unsaturated fatty acids are divided into two groups, omega-6 and omega-3. Some of these fatty acids have other important functions, including producing molecules that regulate many of our bodily functions, such as inflammation and platelet aggregation, which occurs during blood clotting. The derivatives of omega-6 promote inflammation and coagulation, those of omega 3 are anti-inflammatory and anti-aggregating.
Furthermore, omega-3 fatty acids help maintain normal cholesterol and triglyceride levels in the blood.
To conclude, even for fats, our required daily amount is not just quantitative, but qualitative too.
An adult should consume a daily amount of fat of between 20 and 35% of the rest of the energy consumed. For a 2500 kcal diet, this percentage corresponds to about 55-97 g of fat (Reference Intake Levels for Nutrients and Energy*). Be careful, however: the amount of saturated fat you consume must not exceed 10% of the energy found in the rest of your diet (so no more than 27 g for a 2500 kcal diet).
Department of Agricultural and Food Sciences
University of Bologna
*Italian Society of Human Nutrition (SINU): LARN – Reference Intake Levels for Nutrients and Energy for the Italian population – 4th edition. SICS ed.