Health Effects of Omega-3 Polyunsaturated Fatty
Acids
By Artemis P. Simopoulos, M.D.
There are two families of essential fatty acids, the omega-6
and omega-3 polyunsaturated fatty acids (PUFA). They are essential
because human beings cannot make them and they must be obtained
from the diet.
On the basis of estimates
from studies in Paleolithic nutrition and modern-day hunter-gatherer
populations, it appears that human beings evolved consuming
a diet that was much lower in saturated fatty acids than
is today’s diet. Furthermore,
the diet contained small and roughly equal amounts of omega-6
and omega-3 PUFA (ratio of 1–2:1) and much lower amounts
of trans fatty acids
than does today’s diet.
The
current Western diet is very high in omega-6 fatty acids
(the ratio of omega-6 to-omega-3 fatty acids ranges between
10–30:1)
because of the recommendation to substitute vegetable oils —corn
oil, sunflower, safflower, cottonseed and soybean oil—that
are high in omega-6 fatty acids for saturated fats to lower
serum cholesterol concentrations. Furthermore, intake of omega-3
fatty acids is much lower today because of the decrease in
fish consumption, and the industrial production of animal feeds
rich in grains containing omega-6 fatty acids, leading to production
of meat rich in omega-6 and poor in omega-3 fatty acids. The
same is true for poultry, eggs and farmed fish. Even cultivated
vegetables contain fewer omega-3 fatty acids than do plants
in the wild. In summary, modern agriculture, with its emphasis
on production, has decreased the omega-3 fatty acid content
in many foods: green
leafy vegetables, animal meats, eggs, and even fish, while
it has increased the amount of omega-6 fatty acids in foods,
leading to high omega-6 intake for the first time in the history
of human beings in many countries around the world. The
traditional diet of Crete (Greece) is consistent with the Paleolithic
diet relative to the omega-6:omega-3 ratio. The Lyon Heart
Study, which was based on a modified diet of Crete, had an
omega-6:omega-3 ratio of 4:1 resulting in a 70% decrease in
risk for cardiac death. The
higher the ratio of omega-6 to omega-3 fatty acids in platelet
phospholipids, the higher is the death rate from cardiovascular
disease. As the ratio of omega-6 PUFA to omega-3 PUFA increases, the
prevalence of type 2 diabetes also increases. A balance between
the omega-6 and omega-3 fatty acids is a more physiologic state
in terms of gene expression, eicosanoid metabolism and cytokine
production.
Today, more is known
about the mechanisms and functions of omega-3 fatty acids
than other fatty acids. Research has shown that docosahexaneoic
acid (DHA)—an omega-3 fatty acid
found in fish oil—is essential for the development of
the premature infant relative to visual acuity, visual function
and maturation. In the full term infant, DHA may influence
visual acuity and neural pathways associated with the developmental
progression of language acquisition. These findings have led
to inclusion of DHA and arachidonic acid (AA), an omega-6 fatty
acid, in infant formula by most countries around the world.
When humans ingest fish or fish oil, the ingested EPA and
DHA partially replace the omega-6 fatty acids [especially AA]
in cell membranes, particularly those of platelets, erythrocytes,
neutrophils, monocytes and liver cells. Recent research suggests
that the response to omega-3 fatty acids may be genotype dependent,
since certain individuals respond more than others. It is essential
to take genetic variation into consideration in setting up
clinical intervention trials. There is a need to move away
from the long-term prospective studies, and proceed with genotype
specific clinical intervention trials.
Most of the research on the role of omega-3 fatty acids in
chronic diseases has been carried out in patients with coronary
heart disease. Intervention trials have clearly shown that
omega-3 fatty acids have anti-inflammatory, antithrombotic,
hypolipidemic and antiarrhythmic properties, and decrease sudden
death and all cause mortality in the secondary prevention of
coronary heart disease and in one study also in the primary
prevention. Omega-3 fatty acids lower c-reactive protein (CRP)
more so than any other nutrient, which accounts for decreasing
the risk for coronary heart disease. The decrease in sudden
death is most likely due to the antiarrhythmic effects of omega-3
fatty acids. Inflammation and cell proliferation are at the
base of many chronic diseases and conditions, especially atherosclerosis
and cancer, but also diabetes, hypertension, arthritis, mental
health, and various autoimmune diseases. Individuals carrying
genetic variants for these conditions are much more prone to
develop them because the high omega-6:omega-3 ratio leads to
pro-inflammatory and pro-thrombotic states.
The time has come to return the omega-3 fatty acids into the
food supply and decrease the omega-6 intake. There is good
scientific evidence from studies on the Paleolithic diet, the
diet of Crete, other traditional diets (Okinawa), intervention
studies, and finally studies at the molecular level using transgenic
rodents that the physiologic omega-6:omega-3 ratio is 1:1 or
2:1. Japan has already recommended a ratio of 2:1. Industry
has moved in the direction of including omega-3 fatty acids
in various products starting with omega-3 enriched eggs, which
are based on the Ampelistra (Greek) egg as a model obtained
under complete natural conditions and which has a ratio of
omega-6:omega-3 of 1:1.
In the past, industry focused on improvements in food production
and processing to increase shelf life of the products, whereas
now and in the future the focus will be on nutritional quality
in product development. This will necessitate the development
of research for the nutritional evaluation of the various food
products and educational programs for professionals and the
public. The definition of food safety will have to expand in
order to include nutrient structural changes and food composition.
The dawn of the twenty-first century will enhance the scientific
base for product development and expand collaboration among
agricultural, nutritional, and medical scientists in government,
academia and industry. This should bring about a greater involvement
of nutritionists and dieticians in industrial research and
development to respond to an ever-increasing consumer interest
in the health attributes of foods. #
Artemis P. Simopoulos, M.D. is the President of The Center
for Genetics, Nutrition and Health in Washington, D.C. and
author of The Omega Diet (Harper Collins, 1999)
