Essential fatty acids are substances that an animal organism — which includes that of humans — needs for certain physiological and metabolic processes. This is almost a definition of vitamins, and they were indeed known as vitamin F in the early days, but the daily requirement of them is so much greater than that of vitamins that the name has lapsed for them. The need for them was discovered in 1929 when two American scientists, G. O. and M. M. Burr, were studying the effect on rats of fat‐free diets. Many of the effects that were noted and traced to an absence of certain fatty acids could be generalised as the results of an impairment of biological membrane function.