in which the constituent hydrocarbon
chain possesses two or more carbon–carbon double bond
s. Polyunsaturated fat can be found mostly in nuts, seeds, fish, seed oils, and oyster
s. "Unsaturated" refers to the fact that the molecules contain less than the maximum amount of hydrogen (if there were no double bonds). These materials exist as cis
or trans isomers
depending on the geometry of the double bond.
have hydrocarbon chains which can be most readily aligned. The hydrocarbon chains in trans fats align more readily than those in cis fats, but less well than those in saturated fats. In general, this means that the melting points of fats increase from cis to trans unsaturated and then to saturated. See the section about the chemical structure of fats
for more information.
The position of the carbon-carbon double bonds in carboxylic acid
chains in fats is designated by Greek letters
. The carbon atom closest to the carboxyl group
is the alpha
carbon, the next carbon is the beta
carbon and so on. In fatty acids the carbon atom of the methyl group
at the end of the hydrocarbon chain is called the omega
carbon because omega
is the last letter of the Greek alphabet. Omega-3 fatty acid
s have a double bond three carbons away from the methyl carbon, whereas omega-6 fatty acid
s have a double bond six carbons away from the methyl carbon. The illustration below shows the omega-6 fatty acid, linoleic acid
While it is the nutritional
aspects of polyunsaturated fats that are generally of greatest interest, these materials also have non-food applications. Drying oils
, which polymerize
on exposure to oxygen
to form solid films, are polyunsaturated fats. The most common ones are linseed (flax seed) oil
, tung oil
, poppy seed oil
, perilla oil
, and walnut oil
. These oils are used to make paints
In preliminary research, omega-3 fatty acids
in algal oil, fish oil, fish and seafood have been shown to lower the risk of heart attacks
. Other preliminary research indicates that omega-6 fatty acids
in sunflower oil
and safflower oil
may also reduce the risk of cardiovascular disease.
Among n-3 fatty acids Omega-3
, neither long-chain nor short-chain forms were consistently associated with breast cancer risk. High levels of docosahexaenoic acid
(DHA), however, the most abundant n-3 PUFA Omega-3
in erythrocyte ( red blood cell
) membranes, were associated with a reduced risk of breast cancer. The DHA
obtained through the consumption of polyunsaturated fatty acids is positively associated with cognitive and behavioral performance. In addition DHA
is vital for the grey matter structure of the human brain
, as well as retinal stimulation and neurotransmission
Dietary intake of polyunsaturated fatty acids
is under preliminary research to assess the risk of developing amyotrophic lateral sclerosis
(ALS, Lou Gehrig
The importance of the ratio of omega-6/omega-3 essential fatty acids as established by comparative studies shows an Omega-6:Omega-3 ratio under 4:1 may contribute to health.
Contrary to conventional advice, an evaluation of evidence from 1966-1973 pertaining to the health impacts of replacing dietary saturated fat
with linoleic acid found that participants in the group doing so had increased
rates of death from all causes, coronary heart disease, and cardiovascular disease. Although this evaluation was disputed by many scientists, it fueled debate over worldwide dietary advice to substitute polyunsaturated fats for saturated fats.
Polyunsaturated fat supplementation does not decrease the incidence of pregnancy-related disorders, such as hypertension
, but may increase the length of gestation
slightly and decreased the incidence of early premature births.
Expert panels in the United States and Europe recommend that pregnant and lactating women consume higher amounts of polyunsaturated fats than the general population to enhance the DHA status of the fetus and newborn.
Results from observational clinical trials
on polyunsaturated fat intake and cancer have been inconsistent and vary by numerous factors of cancer incidence, including gender and genetic risk. Some studies have shown associations between higher intakes and/or blood levels of polyunsaturated fat omega-3s and a decreased risk of certain cancers, including breast
and colorectal cancer
, while other studies found no associations with cancer risk.
Food sources of polyunsaturated fats include: