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Monthly Health Review, September 2002
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Fats / Lipids
Fats are interesting! Fats can be fun! Our state of health depends on
some fats!
Fats and oils often appear to get a bad press, generally because they
are largely misunderstood. It should be borne in mind that dietary extremes
may lead to imbalances of important fats/lipids in the diet.
The aim of this newsletters is to provide an overview on the
role of fats in the diet.
The word 'lipid' is often used when discussing the metabolism of fats
in the content. Biochemists gave the name 'lipids' to substances that are
insoluble or poorly soluble in water but soluble in organic solvents.
(1).
Fats and oils arrive in different forms. Fatty acids are made up from
carbon and hydrogen atoms linked or bonded together in different patterns.
The bonding pattern determines the properties of the oil or fat. Saturated
fats have a fatty acid with a single bond, monounsaturated fatty acids
have one double bond and the essential polyunsaturated fatty acids have
two or more bonds.
Essential fats - can only be derived from the diet and are needed
to maintain a normal healthy physiology. Excessive amounts of other types
of fats can hinder the absorption of the beneficial essential (polyunsaturated)
fats.
Hydrogenation - is the treatment of unsaturated lipids with hydrogen
to make them more saturated. The process is typically used with oils to
make them solid enough to use in margarine, spreads and shortening production (2).
Hydrogenation also makes oils more stable when exposed to oxygen
in the air.
Monounsaturated fats - olive oil is predominantly monounsaturated,
this is particularly useful for cooking because the molecular structure
of the oil does not change when it is heated. This results in a structurally
more stable oil than other types of oils and fats. Monounsaturated fatty
acids may contribute to improving the balance of blood cholesterol levels.
Polyunsaturated fats - are known as essential fats and must be
derived from the diet - they are found in many plants such as evening
primrose, sunflower, safflower, olives and linseed and also in fish. There
are different groups of polyunsaturated fats, omega-3 from fish (and linseed)
oils; omega-6 from evening primrose, Borage, sunflower, safflower and
others.
Saturated fats - are not classed as 'essential'. Saturated fats
are mostly derived from animal sources. The human content is capable of producing
saturated fat from overindulgence of other fats, carbohydrates and proteins
to store energy and insulate the content.
Trans-fats - partial hydrogenation can change the naturally occurring
"cis" fatty acids into the harmful "trans" form. Structurally, a "trans"
fatty acid is like the 'mirror image' of the "cis" form and therefore
has an opposite effect (similar to that of a saturated fat).
Triglycerides - are molecules comprising glycerol and three fatty
acids. There are 15 - 20 different fatty acids commonly found in oils.
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When is oil
an oil and fat a fat?
Oils are liquid at room temperature (18?C). Fats are
solid at room temperature. However, by forcing hydrogen through oil during
the process of hydrogenation, oils can be manufactured to remain almost
solid at room temperature.
Non-hydrogenated vegetable margarine with no (or low)
trans-fats appear to be a healthier alternative to hydrogenated spreads.
Oils and fats in the diet should not be hydrogenated
and are best consumed as unprocessed as possible, although we have to
process seeds or nuts, by crushing or grinding them to obtain the oils.
The fresher oils are when we consume them, the better they are for us.
Antioxidants may be added, usually in the form of Vitamin E, to help protect
the oils from going rancid (oxidation), especially in food supplements.
Functions of Fat in the Diet (3)
Fat has four main functions:
- As a source of energy, fat contains a higher calorific value than
either carbohydrate or protein.
- Fat helps to make the diet more palatable, it contributes to the
"satiation" factor in eating.
- Fats provide the content with essential polyunsaturated fatty acids.
- Fat-soluble vitamins A, D, E and K are carried in fats.
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The Essential
Polyunsaturated Fatty Acids (PUFAs) and Health
Polyunsaturated fats are important to human health
because they are involved in all cell membrane structures, in particular
helping to maintain the health of the Skin and its permeability to water.
PUFAs are precursors of prostaglandins, short-lived hormone like substances
that have anti-inflammatory action. Prostaglandins derived from omega-3
fats are termed PG3, whereas those from omega-6 fats produce PGE1; this
includes prostacyclins, formed in arterial walls. Prostacyclins are among
the most powerful known inhibitors of platelet aggregation; they also
relax arterial walls and promote a lowering of blood pressure (1).
Whereas, saturated fats are precursors to PG2 prostaglandins,
which have an inflammatory action. PG2 however, is important for thromboxane
production needed in Wound healing.
Blocking Factors of Fatty Acids into Prostaglandins
Various factors affect the efficient conversion of
omega-3 and 6 fatty acids into beneficial prostaglandins. These are viruses,
excess cholesterol, saturated fats, trans-fatty acids, excess dietary
sugar, alcohol, ageing, excessive amounts of alpha-linoleic acid from
plant oils, together with low amounts of certain nutrients vitamins B3,
B6, C, Biotin, and minerals Magnesium, Calcium, Selenium, and Zinc.
Diets that are low in simple and refined carbohydrates
and processed fats should be encouraged in those who need to benefit from
the essential fats in food. Lifestyle factors are also worth considering
- these could include low alcohol intake, moderate exercise, and as Stress-free
a life as possible!
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Some research
on the role of essential fats
Recently, research has found that the omega-3 fatty
acids in Fish Oil may help to suppress the signals responsible for sudden
changes in mood. This may particularly benefit those who suffer with Depression
(4).
Two recent studies have reported that either consuming
large amounts of fish or taking Fish Oil capsules can significantly reduce
the risk of cardiac problems. The first study found that men who consumed
the most fish, regardless of age or Smoking habits, were 81% less likely
to suffer a cardiac death compared to those who ate little or no fish.
Men who consumed modest amounts of fish had a 72% lower risk of cardiac death
(5).
The second study monitored the health of 111,000 patients
who had suffered heart attacks. All subjects were encouraged to follow
a Mediterranean style diet and some were also given a daily 1000mg fish
oil supplement providing eicosapentaenoic acid (EPA) and docosahexaenoic
acid (DHA). During the three and a half years of the study, it was noted
that subjects taking Fish Oil capsules were significantly less likely
to suffer a cardiac related death (6).
Studies clearly show that omega-3 fatty acids can help
to reduce the risk of Coronary Heart Disease. Women especially should
try to eat more oily fish, but as this is not always possible due to dietary
preferences and lack of time; a good alternative is an omega-3 fatty acid
supplement (7).
Amongst the studies demonstrating the benefits from
the regular use of omega-3 fatty acids, it has been noted that EFAs can
offer protection against some degenerative disease in the elderly. A group
of researchers have studied the effects of EFAs on common eye diseases.
Regular intakes of omega-3 in the form of oily fish may have a preventative
effect on the two most common eye diseases leading to blindness (8).
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Recommended
Dietary Fat Intakes
The last report concerning "Dietary Reference Values
for Food, Energy and Nutrients in the UK" (COMA, 1991) recommends the
following advice:
- The total fat content of the diet should provide no more than 33%
of the total energy intake.
- No more than 10% of the total energy intake should come from saturated
fats.
- Approximately 6% of the total energy intake should come from polyunsaturated
fats.
- Approximately 12% of the total energy intake should come from monounsaturated
fats.
- Trans fats should provide no more than 2% of the total energy intake.
Reducing saturated and trans fats in the diet may be achieved by different
methods:
- Eating less red meat but more chicken and fish.
- Being sparing with butter and/or using unhydrogenated spread.
- Not using additional fat in cooking - boiling, grilling or steaming
rather than frying.
- Using monounsaturated fat for cooking rather than saturated or polyunsaturated
fats because monounsaturated (olive oil) is more stable when heated.
- Eating more non-fat foods like vegetables and fruit. They are higher
in fibre and help the Digestive System process fats.
Like all things, fat in moderation is beneficial to health. However,
the type of fat consumed is important. Processed, refined fats (and foods)
should be kept to a minimum. Olive oil is good for cooking because it
is more stable when heated. Non-hydrogenated spreads (or butter) are preferable
for spreading because they are less processed than the hydrogenated varieties
which cause the naturally occurring 'cis' fats to become harmful 'trans'
fats. Our state of health depends on some fats!
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References
- "Human Nutrition & Dietetics" Garrow, James and Ralph. Churchill
Livingstone. 2000.
- Longman Food Science Handbook, Ed. Dr Nicholas Light. Longman,
1992.
- Food Science, Nutrition and Health (Ed. 6) Fox & Coleman. Edward
Arnold, 1995.
- The Lancet, 1999, 353; 9165:1682.
- New Eng. J Med., 2002, 346:1113-1118.
- Circulation: 2002, 105 (19): 2303-2308.
- JAMA. 2002;287:1815-1821.
- Acta. Opthalmol.Scand 1999:77 supp;.229):54-55 & 2. Am.J.Clin.Nutr
2000:73:209-218.
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