Fats and fatty acids

From a biochemical perspective, fats belong to a broader group of substances known as lipids, a large and chemically diverse class of organic compounds. Lipids include not only fats and oils but also waxes, phospholipids, and sterols (such as cholesterol). In the context of human nutrition, the term “fats” typically refers to triglycerides, which make up the vast majority of dietary fat. A triglyceride consists of three fatty acids attached to a glycerol backbone. Dietary fats are complex chemical mixtures, containing various saturated and unsaturated fatty acids in differing proportions. These mixtures often include minor amounts of other fatty and non-fatty components, making each fat source unique in its composition and biological effects. The specific types and ratios of fatty acids in a given fat or oil significantly influence its physical properties (such as whether it is solid or liquid at room temperature) as well as its nutritional and metabolic impacts. Because of this chemical diversity, understanding the structure and function of individual fatty acids is essential when evaluating the health implications of different types of dietary fats.

Fatty acids can originate from exogenous dietary sources or be produced endogenously via de novo lipogenesis. Based on the number of double bonds in their hydrocarbon chains, they are commonly classified into three main categories. Monounsaturated fatty acids (MUFAs) can be found in foods such as fish, plant-derived oils (e.g., olive and canola oil), nuts, and seeds. Polyunsaturated fatty acids (PUFAs) are presented in soybean, corn, and sunflower oils, as well as in some nuts, seeds, tofu, and fatty fish. Saturated fatty acids (SFAs) are predominantly found in animal products (meat, butter, dairy) and in tropical oils like palm oil. A fourth category, trans fatty acids (TFAs), is formed either industrially during partial hydrogenation of vegetable oils (e.g., in some margarines and baked goods), or naturally in small amounts in ruminant-derived products like beef, lamb, and dairy. Due to their negative effects on cardiovascular health, intake of saturated and trans fats should be minimized.

Some polyunsaturated fatty acids are essential, meaning they cannot be synthesized by the human body and must be obtained through the diet. These include omega-3 and omega-6 fatty acids. While both are important for human health, an imbalanced intake (especially the excessive consumption of omega-6s relative to omega-3s) is associated with proinflammatory and prothrombotic effects, contributing to the development of atherosclerosis, obesity, and type 2 diabetes. The modern Western diet often features an omega-6 to omega-3 ratio as high as 20:1, whereas an optimal ratio is believed to be closer to 1:1 to 4:1. This imbalance is further exacerbated by the fatty acid composition of meat from intensive farming systems, which tend to be rich in omega-6 fatty acids due to the animals’ grain-based diets. In contrast, meat from extensive, pasture-based systems contains higher levels of beneficial omega-3s, contributing to a more favorable dietary ratio. Key essential fatty acids include for example alpha-linolenic acid (ALA) or linoleic acid (LA). Alpha-linolenic acid is an omega-3 fatty acid found in flaxseeds, walnuts, rapeseed, legumes, leafy greens, and fatty fish. It has been reported that ALA has cardiovascular-protective, anti-cancer, neuro-protective, anti-osteoporotic, anti-inflammatory, and antioxidative effects. ALA is converted into eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which have crucial roles in brain development, cardiovascular health, and inflammatory reactions. Linoleic acid is an omega-6 fatty acid, which is considered to be involved in reducing incidence of cardiovascular diseases, metabolic syndrome or type 2 diabetes. But LA can also elongate and desaturate to arachidonic acid, which is a precursor of pro-inflammatory compounds that can have a negative effect on health. It is therefore important to balance the intake of a given fatty acid correctly. Maintaining a proper equilibrium in the consumption of a specific fatty acid is crucial.

Fatty acids play numerous physiological roles. They are primary structural and functional components of cellular membranes, particularly as part of phospholipids. The type of fatty acids incorporated into membranes influences membrane fluidity, thickness, and function. For example, membranes rich in short-chain saturated fatty acids are more viscous, whereas membranes containing MUFAs and PUFAs are more fluid. This has clinical relevance: greater membrane fluidity (due to unsaturated fatty acids and lower cholesterol) enhances insulin receptor density and sensitivity, potentially reducing insulin resistance. Fatty acids are a major source of energy through β-oxidation. When not immediately needed, they are stored as triacylglycerols or sterol esters in lipid droplets, serving as energy reservoirs or substrates for membrane synthesis. Lipids also have the capacity to accumulate lipophilic xenobiotic compounds, potentially leading to lipotoxicity and apoptosis. They are precursors of eicosanoids, which are bioactive compounds involved in inflammation, immune regulation, blood pressure control, gastric protection, and smooth muscle activity. Ecosanoids also serve as signaling molecules and are essential for hormone production. Fats provide essential fatty acids and are critical for the absorption of fat-soluble vitamins (A, D, E, and K). However, excessive fat intake, particularly in Western diets, may disturb gut microbiota composition and reduce bioavailability and efficacy of these vitamins, potentially leading to toxicity. Omega-3 PUFAs, especially DHA, are essential for brain development, retinal function, anti-inflammatory signaling, and cardiovascular health. DHA functions as a neurotrophic factor, supports synaptic activity, and contributes to atherosclerosis prevention. Additionally, fat plays a role in water storage, a function particularly vital for desert-adapted species like camels, although less relevant in human physiology.

Cardiovascular diseases (CVD) remain one of the leading causes of mortality in developed countries (see Figure 2.). The underlying pathological process is most often atherosclerosis, a chronic and progressive condition characterized by the thickening and loss of elasticity of arterial walls due to the accumulation of lipids, connective tissue, and, in advanced stages, calcium deposits. As atherosclerotic plaques develop, arterial narrowing occurs, which can impede blood flow and lead to tissue ischemia. The most common acute clinical manifestations of atherosclerosis-related CVD include myocardial infarction (heart attack, typically caused by a thrombus that forms over an atherosclerotic lesion in the coronary artery, blocking blood flow to part of the heart muscle) and ischemic stroke (often due to a blockage in the carotid artery, reducing or halting blood flow to the brain). The development of atherosclerosis is multifactorial, involving both genetic predispositions and lifestyle-related risk factors, including dietary fat intake. Although some findings in the literature are conflicting or remain under debate, certain trends are well established regarding the effects of different types of fatty acids on cardiovascular health. Evidence about MUFAs suggests a neutral or protective effect, depending on the overall dietary context. Diets high in MUFAs, such as the Mediterranean diet, are consistently linked with lower cardiovascular risk. PUFAs, especially omega-3 fatty acids (EPA and DHA), are also associated with reduced risk of CVD. These fatty acids exert anti-inflammatory, antithrombotic, and antiarrhythmic effects. On the other hand, SFAs are generally associated with a higher risk of CVD, particularly when consumed in large quantities and in the context of low intake of protective nutrients like fiber or omega-3 fatty acids. TFAs are also strongly associated with increased cardiovascular risk due to their adverse effects on blood lipid profiles and endothelial function. Although not a fatty acid, cholesterol is an important lipid molecule frequently discussed alongside dietary fats due to its close association with blood lipid profiles and cardiovascular health. On its own, dietary cholesterol has a minimal or negligible impact on CVD risk, especially when saturated fat intake is accounted for. An illustrative example comes from populations such as the traditional-living Greenland Inuit, who exhibit low incidences of cardiovascular disease despite high fat consumption. Their diet is rich in very long-chain omega-3 PUFAs, especially EPA and DHA, which are believed to play a significant role in their cardiovascular protection.