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Fish
Although a forkful of fish is a
gold mine of concentrated nutrients, North Americans consume an average of
only 15 lb (6.8 kg) a year, compared to the annual per capita intake of beef
and chicken of close to 100 lb (45 kg). While these statistics seem to
indicate a clear culinary preference for beef and chicken, there are
important health benefits to be gained from eating more fish and less meat.
The average Western diet provides
about twice as much protein as necessary; in itself, this might not be a
problem except that our typical protein choices with large quantities of
saturated fats. in contrast, fish and shellfish are rich in protein with
fewer calories, and less fat per serving than most meats. The fats in fish
are particularly high in polyunsaturates, which remain liquid even when
chilled. (If fish had a lot of saturated fat, it would congeal into a solid
mass and prevent them from moving in their cold-water habitat.) And although
some shellfish do contain cholesterol, they are low in saturated fats and
are no more likely to increase blood cholesterol than skinless poultry.
HEALTH BENEFITS
Eating fish three times a week
has been associated with a significant decrease in the rate of heart
disease. This became apparent when scientists noted that coronary artery
disease – a leading cause o death in North America – was almost nonexistent
among the indigenous people of Greenland, Japanese fishermen, and First
Nations of the Pacific Northwest. The one factor that these three groups had
in common was a diet that relied heavily on fish for protein. When
researchers looked at the effects of diets in other populations, they found
that men who ate fish regularly two or three times a week were much less
likely to suffer heart attacks than men who shunned fish.
In the recent Physicians Health
Study, the male participants who ate fish at least once a week were 52
percent less likely to die of a heart attack than men who are fish once a
month or less. It's not yet known whether the effect is due to one factor or
many, but evidence so far points to the beneficial action of fish oils. Fish
oils are rich in a type of unsaturated fatty acid known as omega-3. These
fatty acids decrease the stickiness of blood platelets, making it less
likely that they will clump together to form clots. They also increase the
flexibility of red blood cells, enabling them to pass more readily through
tiny vessels, reduce inflammation of the artery walls, and lower levels of
triglycerides in your blood.
A study of more than 43,000 men,
published in 2003, showed that men who ate about 3 to 5 oz (85-140 g) of
fish one to three times a month were 43 percent less likely to have an
ischemic stroke, the most common type of stroke, which is caused by blood
clots.
The human body uses omega-3 fatty
acids to manufacture prostaglandins, chemicals that play a role in many
processes, including inflammation and other functions of the immune system.
Several studies have found that a diet that includes fish oil equivalent to
the amount in an 8-oz (230-g) daily serving of fish could relieve the
painful symptoms of rheumatoid arthritis. Researchers believe that the
beneficial effect was due to omega-3 fats, especially eicosapentaenoic acid
(EPA). This fatty acid seems to promote the production of forms of
prostaglandins and other substances that are less active in inflammation
than those derived from saturated and polyunsaturated fats. The
anti-inflammatory effects of omega-3 fats are being studied as a possible
treatment for Crohn's disease and ulcerative colitis.
Some studies also suggest that
people whose at fish regularly (especially varieties rich in omega-3s) are
less likely to suffer from a decline in age-related thinking skills such as
memory. Other studies slink low levels of omega-3s to higher rates of
depression.
A study from Australia involving
more than 3,500 older adults found that eating fish just one to three times
per month appeared to protect participants against age-related macular
degeneration, the leading cause of blindness in older adults.
NUTRITIONAL VALUE
All fish are rich in nutrients,
especially protein, niacin, vitamin B12, zinc, magnesium, and more. Oily
fish are particularly rich in vitamins A and D. In addition, the bones in
canned salmon and sardines are an excellent source of calcium.
Fish are high in protein because
they carry a massive bulk of muscle on a much more spindly skeleton than
land animals do. Contrary to popular belief, it's not necessarily true that
the darker the flesh, the oilier the fish; the dark color is, in fact, due
to the presence of myoglobin, a pigment that stores oxygen in the muscles.
The flesh of salmon and trout gets its appealing pink color from astaxanthin,
a carotenoid pigment derived from the crustaceans and insects the fish feed
on. the diet of farmed fish is often fortified with carotenoids to enhance
the pink color of the flesh.
There is no difference in
nutrient content between fish that are farmed and those caught in the wild.
However, some farmed fish, such as salmon and trout, have a texture that is
mealier than that of their wild counterparts. There is some concern that
farmed fish may contain PCBs since these substances are more likely to be
found as contaminants in coastal waters.
HOW MUCH IS ENOUGH ?
The mounting evidence about
fish-linked cardiovascular benefits led the American Heart Association to
include eating two servings of fish a week in its updated dietary
recommendations. Some experts suggest up to three servings of fish a week
are needed to provide the benefits attributed to omega-3 fatty acids.
Fish oil supplements may be
advisable for some people, but check with your doctor first since they can
"thin" the blood. Look for a product with a combination of DHA and EPA (two
omega-3 fatty acids). Avoid fish liver oil capsules, which are a
concentrated source of vitamins A and D. These vitamins can be toxic when
taken in large amounts for long periods.
HEALTH RISKS
Some raw fish preparations,
particularly sushi, can harbor parasites. Dutch "green" herring and
Scandinavian gravlax (picked salmon) are also raw, but the pickling process
used in herring and properly made gravlax eliminates worms and eggs.
Oily fish, like fresh herring and
mackerel, must be cooked or processed soon after they are netted. If kept
too long before cooking they are susceptible to bacterial growth, which can
cause scombroid poisoning, characterized by a rash and stomach upset.
Shellfish from waters polluted by
human waste bring a threat of viral hepatitis as well as bacterial
infections that can cause severe gastrointestinal upset. Shellfish farms are
required to meet strict health standards to ensure that their products are
safe, but bacterial contamination still occurs. The old rule of eating raw
oysters only in the "R" months does have some validity since bacteria are
more likely to survive in warmer waters. thorough cooking destroys the
bacteria that can contaminate oysters.
Coastal waters are, at times,
tinged red by a species of algae (Karenia brevis) in a phenomenon
known as "red tide." Shellfish from red tide areas should not be eaten
because they concentrate a toxin produced by the algae. eating contaminated
shellfish brings on symptoms of poisoning within 30 minutes: facial
numbness, breathing difficulty, muscle weakness, and sometimes partial
paralysis. Ciguatera poisoning is similar, and is caused by a toxin produced
by a species of plankton. the plankton are consumed by fish, which then pass
the poison on to the humans. In some cases, the effects of this toxin have
lasted more than 20 years.
Large, long-lived fish, such as
tuna, shark, king mackerel, and swordfish, may accumulate heavy-metal
contaminants – especially mercury – which are toxic to the human nervous
system and can be dangerous for unborn babies. Because of this potential
hazard, women should either avoid these fish completely during pregnancy or
eat them no more than once a month. In terms of canned tuna, albacore tends
to be higher in mercury than light tuna. Some consumer groups recommend that
pregnant women eat no more than 6 oz (170 g) of light tuna every 4 days – 10
days for albacore.
Some species of fish caught in
certain areas may show high levels of PCBs and other industrial pollutants;
they are best avoided. Pregnant women are advised not to eat striped bass,
especially from the northeastern regions, which may accumulate oil residues.
Check with your local health department before eating fish caught in local
streams and lakes. They may contain pollutants that are harmful.
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