Polyunsaturated fats are a category of dietary fats. Since the body cannot produce them, it is necessary to obtain them from food. These fats are involved in many bodily functions, and consuming them as part of a balanced diet can have a positive effect on health.
Understanding PUFA Categories
Polyunsaturated fatty acids (PUFAs) are chemically distinguished by having more than one double bond in their carbon chain. This structure makes them behave differently in the body compared to saturated fats, which have no double bonds. The two main families of PUFAs are omega-3 and omega-6, and the naming convention refers to the location of the final double bond in their chemical structure, counting from the methyl, or “omega,” end of the fatty acid molecule.
The primary types of omega-3s are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). The main omega-6 fatty acids are linoleic acid (LA) and arachidonic acid (ARA). Because the body cannot synthesize ALA and LA on its own, they are termed “essential” fatty acids. The body can convert ALA into EPA and DHA, and LA into ARA, but the conversion is often inefficient.
Essential Dietary Sources
Omega-3 ALA is primarily found in plant-based sources. Flaxseeds, chia seeds, and walnuts are rich in ALA, as are plant oils like canola and flaxseed oil. The other major omega-3s, EPA and DHA, are found in marine sources. Fatty fish are excellent sources of these fats, including:
- Salmon
- Mackerel
- Herring
- Sardines
For individuals who do not consume fish, algae oil provides a direct plant-based source of DHA and EPA.
Omega-6 fatty acids are widespread in the modern diet. Linoleic acid (LA) is abundant in many common vegetable oils, including soybean, corn, and sunflower oils, as well as various nuts and seeds. Arachidonic acid (ARA) is found in smaller amounts in animal products like meat, poultry, and eggs. Due to the prevalence of vegetable oils in processed foods, most people consume significant quantities of omega-6s.
Functions in Human Health
PUFAs are integral components of cell membranes, influencing their fluidity and flexibility. This property affects the function of receptors and enzymes within the membrane, impacting cell signaling and transport processes. A membrane with a higher concentration of these fatty acids is more fluid, which can enhance cellular communication.
DHA is highly concentrated in the brain and retina, where it accumulates during fetal and infant development. It is a major structural fat in the cerebral cortex and is involved in learning, memory, and visual acuity. DHA supports the structure and function of photoreceptor cells in the eye and neurons in the brain.
The body uses omega-3 and omega-6 fatty acids to produce signaling molecules called eicosanoids. These hormone-like compounds help regulate blood clotting, blood pressure, and inflammatory responses. Eicosanoids derived from omega-6 ARA tend to be more pro-inflammatory, while those from omega-3 EPA are generally less inflammatory. This difference significantly impacts cardiovascular health.
Achieving a Healthy PUFA Balance
The relative proportion of omega-6 to omega-3 fatty acids in the diet is a factor for long-term health. Historically, human diets contained a ratio of omega-6 to omega-3 that was close to 1:1. Modern Western diets, heavy in processed foods and certain vegetable oils, have shifted this balance, with ratios often estimated to be as high as 15:1 or greater.
This imbalance can have health consequences. Because omega-6 and omega-3 fatty acids compete for the same enzymes to produce eicosanoids, an overabundance of omega-6s can lead to more pro-inflammatory signaling molecules. This state is thought to contribute to a low-grade, chronic inflammation that underlies many modern health issues.
Achieving a healthier balance does not mean eliminating omega-6 fats, as they are essential. The focus should be on moderating the intake of omega-6-rich oils and increasing the consumption of omega-3-rich foods. This can be accomplished by using oils like olive or canola oil for cooking, eating fatty fish weekly, and incorporating foods like flaxseeds and walnuts. This dietary shift helps recalibrate the production of eicosanoids toward a less inflammatory state.