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We now know that major changes have taken place in the food supply over the last 100 years, when food technology and modern agriculture led to enormous production of vegetable oils high in ω-6 fatty acids, and changed animal feeds from grass to grains, thus increasing the amount of ω-6 fatty acids at the level of LA (from oils) and arachidonic acid (AA) (from meat, eggs, dairy).
This led to very high amounts of ω-6 fatty acids in the food supply for the first time in the history of human beings. Traditionally, animals grazed. Grass contains ALA (ω-3), whereas grains, corn and soya (which are now fed to animals) are high in LA (ω-6).
This imbalance in the amount of ω-6 and ω-3 fatty acids is a new phenomenon that was never a part of human evolution (figure 1, table 2). Human beings evolved on a diet that had equal amounts of ω-6 and ω-3 fatty acids. This balanced ratio of ω-6 to ω-3 is critical to human development during pregnancy and lactation, in the prevention of chronic diseases and in their management.
The typical Western diet now provides an ω-6 to ω-3 ratio of around 16:1. High dietary intake of ω-6 fatty acids as occurs today leads to increases in white adipose tissue and chronic inflammation, which are the ‘hallmarks of obesity’.
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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5093368/pdf/openhrt-2015-000385.pdf
