Fats and oils are a subgroup of lipids. Other than these two, there are also phospholipids and sterols, but they are far less included in human diet. Fats and oils are triglycerides, esters derived from glycerol and three fatty acids that determine molecule properties.
First of all, we have state of matter (fats are solids and oils are liquids at room temperature) and then the effects they have on the human organism. Fatty acids are shaped like chains, and we divide them into saturated (SFA) with no double bonds in their chemical structure, and unsaturated that have at least one. Fats, usually obtained from animal sources, have mostly SFA which is why they are solids at room temperature. On the other hand, oils from plants have unsaturated fatty acids which make them liquid at room temperature. Depending on the number of double bonds, unsaturated fatty acids can be divided into monounsaturated (MUFA) and polyunsaturated (PUFA). We should also mention trans fatty acids (TFA) which can be both MUFA and PUFA, and are characterized by trans- instead of cis- structure. Due to their very negative effect on health, TFA are a topic for a separate article. PUFA, depending on the position of the first double bond from the carboxyl end of fatty acid chain, can be divided into Ω-3, Ω-6 and Ω-9, with numbers 3, 6, and 9 signifying the mentioned position. Both groups are essential for humans, meaning they cannot be synthesized and must be ingested through food. Main representatives of Ω-3 are long chain fatty acids, eicosapentaenoic (EPA) and docosahexaenoic (DHA), and short chain, α-linolenic (ALA) acid. ALA is a precursor in EPA and DHA synthesis, responsible for Ω-3 biological influence, but the success of transformation is only 5%. EPA and DHA are mostly found in blue (fat) fish like sardine, salmon, herring, and mackerel, while ALA is found in flax seeds, rape seeds, and walnuts. Essential Ω-6 fatty acids are arachidonic (AHA) and linoleic (LA), which are precursors in AHA synthesis. LA can be found in many vegetable oils such as sunflower, corn, soy, peanuts, etc. We must mention that all vegetable oils have Ω-3 and Ω-6, only in different ratios. Interestingly enough, the only source where Ω-3 is more present than Ω-6 are flax seeds.
PUFA, and especially Ω-3 and Ω-6 fatty acids, have an important building function in the body. They are an essential component of central nervous system cell membranes where they participate in maintaining the membrane fluidity. This role is especially important in newborns and children, when the speed of nervous tissue growth is the greatest.
Ω-3 and Ω-6 show their biological effects through eicosanoids – they are substrates in their synthesis. Eicosanoids are „messengers“ which bond with receptors of all cells and participate mostly in inflammatory processes and the immune system reply. There are four groups of eicosanoids: prostaglandins, prostacyclins, thromboxanes, and leukotrienes. There are Ω-3 and Ω-6 forms of each of those, depending on the precursor – the fatty acid from which they were produced, and have an opposite effect in the body. While Ω-6 has inflammatory effect, Ω-3 eicosanoids have an anti-inflammatory effect.
The ratio between Ω-3 and Ω-6 intake in a typical Western diet is between 15:1 or 20:1 for Ω-6. Intake ratio reflects on their composition in the tissue. Higher levels of Ω-6 result in greater production of Ω-6 eicosanoids, responsible for inflammatory action. Also, Ω-3 and Ω-6 compete for the same enzymes (desaturases and elongases) included in the process of their transformation into eicosanoids, meaning that a greater production of Ω-6 eicosanoids reduces the production of anti-inflammatory Ω-3 eicosanoids. For this reason, a logical recommendation is to reduce the intake of Ω-6 and increase the intake of Ω-3 fatty acids.
Ω-3 fatty acids intake is connected to many positive effects on human health: reducing the risk for cardiovascular disease (CVD), cancer, Alzheimer's disease, autism, schizophrenia, bipolar disorder, depression, hyperactivity disorder, attention deficit hyperactivity disorder (ADHD) and osteoporosis. The most research was done on cardio protective benefits. Ω-3 fatty acids are one of the most researched items in cardiovascular medicine, even though precise mechanisms of protective effect have not yet been fully explained. Other positive effects aren't researched enough, but preliminary research shows encouraging results. Generally speaking, for the most of the population, the intake of Ω-3 is not high enough. In the US, average daily intake is only 0,1 - 0,2 g/day, while the experts recommend 1 g/day, regardless of it being from food or supplements (capsules or fish oil). But, for certain effects you need a higher quantity and I'll talk about this more in the future articles dealing with the influence of Ω-3 on specific states/illnesses. It's very important to say that the intake of up to 3 g/day has almost no side effects. In higher intake levels, some might feel nauseous (which is a small price to pay if supplementation proves beneficial). Also, the effect of higher intake is different between population groups due to baseline consumption which varies greatly between different parts of the world – for example, between coastal areas and continental areas. People with an existing high intake of Ω-3 probably won't benefit much from extra supplementation.
To keep it real… Since the main source of Ω-3 is fatty sea fish, there's a question of poisoning, because seas and oceans have large quantities of toxic compounds which accumulate in the fatty meat of the fish. This goes for methylmercury, dioxins and polychlorinated biphenyls. Fortunately, concentrations are (still?) not as high to completely avoid sea products, but we must restrict the weekly intake with some species that accumulate toxins more than others, such as tuna fish. Fish that was caught in less polluted seas, such as the Adriatic, does not contain significant amounts of toxins.