fatty acidsbecome essential if there is insufficient
linoleic and aplha-linolenic acid available in the diet.
These fats play a significant role in development of the
brain, nervous system, and retina in fetal development
and early life.
OMEGA-6.The most concentrated sources of
omega-6 in the diet is vegetable oils, such as sunflower,
safflower, corn, cottonseed, canola, and soya oils. They
are also present in plant seeds, nuts, vegetables, fruit
and cereals. In addition to being a source of linoleic
acid, omega-6s have been shown to have a lowering
effect on both LDL and HDL cholesterol. However,
there are health concerns with excessive omega-6
intakes. Omega-6 fats are susceptible to oxidation
within the body and may contribute to tissue damage
that leads to atherosclerosis and cancer. Omega-6 fats
should contribute no more than 10% of dietary energy.
Antioxidant nutrients such asvitamin Eare required to
reduce this oxidation with higher intakes of omega-6
fats. Omega-6s compete with the more beneficial
omega-3 fatty acids, so it is recommended that the
omega-6:omega-3 ratio is reduced to 4:1.
OMEGA-3.Short chain omega-3 fats are found in
flaxseedor linseed oil, walnut oil, canola oil, and
rapeseed oil. The best sources of long chain omega-3s
are fish and fish oil.
Evidence suggests that consuming long chain
omega-3 fats has cadiovascular health benefits. This
believed to be the result of their anti-clotting effect.
Growing evidence also suggests that consuming long
chain omega-3s has benefits beyond those achieved
when consuming shorter chain fatty acids. The United
Kingdom’s government Food Standards Agency rec-
ommends that oily fish be consumed at least once a
week.
There has been much interest in the effect of EPA
and DHA deficiency and supplementation on behavior
in children, particularly those with learning difficulties.
Although there is some evidence of benefit with EPA, in
2006 the U.K. Food Standards Agency concluded that
there was insufficient evidence to reach a firm conclu-
sion and additional clinical trials were needed.
There is also interest in the anti-inflammatory prop-
erties of long chain omega-3s in inflammatory condi-
tions such as Crohn’s disease and rheumatoid arthritis.
The role of omega-3s has been evaluated in treatment of
depression and prevention of cognitive decline but more
research is needed to confirm these benefits.
Omega-3 fats have been shown to reduce blood
pressure and triglyceride levels (another fat in the
blood that contributes to raising the risk of cardiovas-
cular disease). To achieve these benefits, omega-3s
must be taken in pharmacological doses and there are
small risks associated with these high doses such as
raised LDL cholesterol, poor control of diabetes, and
increased risk of bleeding. Large doses of omega-3s
should only be taken under the supervision of a quali-
fied medical doctor.Trans fatty acids
Transfatty acidsare monounsaturated or polyun-
saturated fatty acids where the double bond is in the
transrather thancisformation. They occur naturally in
small amounts in lamb, beef, milk, and cheese as they
are created in the rumen of cows and sheep. The major-
ity oftransfat in the diet comes from the partial hydro-
genation of vegetable oils. This is a process in food
manufacture that adds hydrogen atoms to unsaturated
fatty acids so that oils become more hardened at room
temperature. The process results in some of the double
bonds of the fatty acid molecules becoming saturated
and some of the remaining double bonds changing
from acisto atransformation. For example, when
partially hydrogenated oleic acid becomes elaidic acid
or 9trans-octadecenoic acid.Transfats are semi-solid
at room temperature and more stable within food.
Partial hydrogenation of oils has traditionally been
used to develop spreading fats and margarines, for
fast food, and in cakes and biscuits. Manufacturers
are using it less because of the health problems associ-
ated with it. In 2006, New York City adopted the
United States’ first major ban on all but trace amounts
of artificialtransfats in restaurant cooking. As of July
2008, a serving of food must not contain more than half
agramoftransfat. Food legislation in the United
States and the European Union states that hydrogen-
ated or partially hydrogenated fats must be labeled in
the ingredients of food and in some cases the amounts
oftransfat must also be labeled.
TRANSFATTY ACIDS AND HEALTH.Transfat raises
LDL cholesterol in a similar way to saturated fat and it
reduces HDL cholesterol. It may also raise blood tri-
glyceride levels. The combination of both these effects
means that it is most likely to increase cardiovascular
risk. The World Health Organization recommends
phasing outtransfat in food manufacture and reduc-
ingtransfat consumption to no more than 1% of
dietary energy or 2.5 g per day.Cholesterol
Cholesterol is essential to the structure of cell
membranes and production of bile acids for digestion,
steroid hormones, andvitamin D.Dietary cholesterolFats