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Fish
Oil
Fish oil (high DHA type)
combined with exercise can reduce abdominal
fatness
A study by
Alison Hill, PhD student from the University
of South Australia (abstract
published in Asia pacific Journal of Clinical
Nutrition) showed that 6g (or 6x1g capsules)
of fish oil (high DHA content) daily for
3 months reduced body fat by 5% especially
from the abdominal (visceral) region, only
when combined with moderate aerobic exercise
for 45 minutes 3 times a week. The groups
that were placed on fish oil alone or exercise
alone did not lose abdominal fat.
It is known that omega-3 fatty acids from
fish oil increase the expression of fat
burning enzymes, but until now the implications
of this in humans was not entirely clear.
This study suggests that although fish oil
increases the expression of fat burning
enzymes taking it alone will not have a
significant effect but that it needs a driver
- exercise - to increase metabolic rate
and lower body fat.
This is an
interesting study because the subjects were
not on calorie restricted diets and yet
the fish oil when combined with exercise
facilitated abdominal fat loss and yet the
other groups did not lose body fat. The
fish oil groups also reduced their blood
fats (decreased triglycerides and raised
HDL "good" cholesterol) and improved
blood vessel elasticity.
It would be
interesting to know if you can get similar
results by combining exercise with fatty
fish (e.g tuna) daily or by combining exercise
with lower doses of fish oil (say 1-2g/day)
of the standard variety (EPA/DHA).
2004
Update
Hundreds of studies have been done on fish
or fish oils and prevention or treatment
of heart disease. Most of the effect is
attributed to the fat content called omega-3
fatty acids. A recent review recommends
fish or fish oil supplements to prevent
heart attacks, particularly if someone already
has vascular disease. How omega-3 fats reduce
heart disease is not known, but they lower
blood triglycerides and blood pressure,
prevent clotting, are anti-inflammatory,
and reduce abnormal heart rhythms. Several
large trials have been done with fish oil
capsules in people who had heart attacks,
and the reduction in second heart attacks
has ranged from 30 to 48 percent. The review
was published in the January 3, 2004 edition
of the British Medical Journal.
Fish Oil
Many
GP's prescribe fish oil capsules; these
are valuable for loweering triglyceride
levels,but
fish itself, in modest quantities gives
protection against coronary heart disease
mortality. It appears there is a factor
in fish which increases the potency of it's
important omega 3 fatty acids EPA or eicosapentanoic
acid and DHA or docosahexaenoic acid which
may be absent in fish oil supplements. Two
fish oil capsules (e.g. MAXEPA) or fatty
fish three times a week will provide about
0.5g of EPA/DHA daily. Tissue concentrations
of EPA increase when the diet is supplemented
with linolenic acid, but fish oil is the
most efficient way to increase tissue EPA
because the rate-limiting step (cyclo-oxygenase)
is by-passed.
Fish
oil has not been found to protect against
restenosis after angioplasty (Leaf et al.
Circulation 1994; 90: 2248); the DART study
found that fewer people died suddenly but
recurrent myocardial infarction was not
reduced (Burr et al Lancer 1989; 2: 757-61).
Fish oils may prevent fatal ventricular
arrhythmias. Animals fed pharmacological
doses (10-40g/day) of fish oil have reduced
incidence of cardiac arrhythmia. This is
of considerable interest as arrhythmia is
linked with sudden cardiac death –
a leading cause of heart-related deaths.
Feeding of fish oils to animals has been
shown to protect the myocardium against
the full damage of ischaemia, infarct size
is less, blood flow better maintained and
there is less oxidative damage and calcium
overload, both of which can induce arrhythmias
(Nestel 1991, World Rev Nutr. Diet; 66:
268-77).
Endothelium
dependent dilatation of arteries is enhanced
by fish oils which also inhibit the vasoconstrictive
effects of sympathetic overactivity and
norepinephrine (Chin et al. Hypertension
1993; 21: 22-8). Arterial compliance or
elasticity is improved in diabetics taking
fish oil (McVeigh et al. Arterioscler. Thromb.
1994; 14: 1425-9). Thrombogenic factors
are reduced in people eating fish oils;
bleeding time is prolonged (nearly always
safely), platelet aggregation is inhibited
and thromboxane production in platelets
(a vasoconstrictive effect) is suppressed
(Tremoli et al. AJCN 1995; 61: 607-13).
PAI-I, an inhibitor of plasminogen, is reduced.
Triglyceride
rich lipoproteins are reduced by fish oil
in both the postabsorptive and postprandial
states (Nestel; Ann Rev Nutr. 1990; 10:
149-67). LDL may increase slightly and LDL
isolated from people eating fish oils are
susceptible to oxidation and are potentially
more atherogenic (Suzukawa et al. J Lipid
Res 1995; 36: 473-84). However, enrichment
of the diet with vitamin E prevents this
problem, leading to a proposition that fish
oil should be supplemented with this vitamin.
Summary:
1.Fish
oils exert favourable effects on plasma
triglycerides, platelet aggregation, myocardial
arrhythmogenicity, inflammatory cell response,
vascular reactivity and possibly blood pressure.
2.The
beneficial effects probably outweigh a marginal
increase in LDL concentration and an increased
susceptibility to oxidation which seem to
occur with fish oil consumption.
3.Fish
oil supplements are a safe and often effective
treatment for patients with hypertriglyceridaemia;
they may also help lower blood pressure
and reduce blood clotting. However, the
capsules are expensive and high doses are
required to have a beneficial effect; e.g.
to reduce platelet aggregation. Consistent
effects at lower doses with fish oils have
not been observed. Despite the circumstantial
evidence that fish oil consumption protects
against CHD, there is still no direct proof
of benefit in intervention studies. Eating
two servings of fish a week may help reduce
the risk of CHD. There may be other factors
in fish that contribute to its protective
effect against CHD.
See also
articles omega 3 fatty acids
Last
Updated: March 2006
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