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Video: Fish in your diet

By "Today" show contributor
updated 5/16/2006 12:14:05 PM ET 2006-05-16T16:14:05

On May 11, 2006, a San Francisco judge ruled that tuna companies are not required to put labels on canned tuna warning consumers that the fish contains mercury. California's attorney general had sued several companies, including Del Monte Foods, maker of StarKist brand tuna, Bumble Bee Seafoods, and Tri-Union Seafoods, maker of Chicken of the Sea brand tuna, for violating a state law requiring that they issue warnings for foods that contain “known carcinogens or reproductive toxins.” The ruling says that the mercury levels found in canned fish don't require warning levels. Given this latest news, we thought we'd revisit a column “Today” medical contributor Dr. Judith Reichman wrote last year about what you should consider when you eat fish. Here it is:

We seem to be floundering when it comes to sorting through information about the benefits and dangers of fish consumption.  Is fish “brain food” or is it dangerous for our brains, especially those of developing babies, children and the elderly? Will it prevent heart disease, and if so, do all fish have the right stuff to bestow cardiac benefits? 

Must we get certificates of origin, size, and the eating and swimming habits of the fish before we add this aquatic protein to our diet?  And does the way we cook fish make a difference?  Or are we just better off taking fish oil supplements?

What arethe positive effects of fish consumption?
Fish remains our chief natural source of Omega-3 fatty acids, a fatty acid that our body is unable to produce on its own. Numerous studies have shown that this fatty acid lowers triglycerides, helps prevent abnormal heart rhythms, reduces blood pressure, improve blood clotting and even aids and abets the work of prescription drugs to improve cholesterol levels. It reduces inflammation, helps prevent arthritis and heart disease and promotes healthy brain function. 

Researchers have looked at large populations of women (and men) and have found that those who consume fish more than twice a week have lower heart rates, less irregular heart rates, a decrease in heart disease, fewer heart attacks and even fewer cases of sudden death.  Higher fish consumption has also been found to significantly decrease heart attacks in diabetic women.  Their risk of developing heart disease decreased by 40 percent if they eat fish once a week and 64 percent if they eat it five or more times a week. 

The Omega-3 fatty acid content in fish has also been found to possibly protect against Alzheimer’s disease. 

But we shouldn’t just focus on Omega-3s in our perfuse praise of fish. Fish and shellfish are also a great source of protein and have (depending on type and preparation) less saturated fat, cholesterol and calories than chicken or beef.  Fish contains Vitamin D and can help with calcium absorption and prevention of osteoporosis. 

And there is some data that women who eat a diet rich in fish are a third less likely to get breast cancer than women who seldom eat fish. 

Are all fish created Omega-3 equal?
No, some fish are fattier and have more of this good-for-us fat.  Cold water fish that have the highest amount of Omega-3s include salmon, tuna, mackerel, codfish, rainbow trout and sardines. 

As of April 2005, retail stores are required to label fish for country of origin and indicate if the fish is farmed or wild. 

Does it matter whether fish are wild or farmed when it comes to Omega-3 fatty acids?
In nature, fish accumulate their own fatty acids by eating large quantities of algae and plankton, which contain DHA/EPA (the two most important Omega-3 fatty acids).  Farmed fish may have similar amounts of Omega-3 fatty acids as wild fish, but they have more total fat and calories and tend to have more toxins than wild fish. 

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What about the method of cooking?  Does that have an affect on the cardiac benefit of fish?
One study showed that only broiled or baked fish lowered the incidence of atrial fibrillation, the most common irregular heartbeat among the elderly, which can lead to heart attack and stroke.  In a study of nearly 5,000 men and women over 65 who were followed for 12 years, it was found that those who had five or more servings per week of tuna fish (fresh or canned) or other fish that was broiled or baked had a 31 percent lower risk of atrial fibrillation than those who ate fish less than once a month, but that eating fried fish or fish burgers didn’t lower their risk.

It appears that consumption of fried fish and fish burgers did not raise their Omega-3 fatty acid levels.  The researchers were not sure, however, if the fatty acids were destroyed by frying or if the lower Omega-3 levels were due to the fried fish and fish burgers being cod and pollock, which are lean fish and have fewer Omega-3 fatty acids to begin with. 

Now for the downside.  What should we worry about when it comes to fish consumption? 
The chief concern is that fish may be contaminated with a number of toxins, and when ingested in large quantities, these can adversely affect our health.  And even small amounts may cause developmental injury to a fetus or child. 

Methyl mercury gets into our system through the consumption of fish and sea mammals.  Some of this mercury toxin arises naturally from gas that evaporates from the earth’s soil and water, as well as from the emissions of active volcanoes. But it’s not all nature’s fault; our atmosphere has now been inundated with increasing amounts of mercury gas, produced from coal burning sources and other industrial processes. This mercury vapor then gets into the rain and soil and continues to circulate for years. It enters both nearby and distant bodies of water, attaches to aquatic sediment and microorganisms such as algae, and is converted to methyl mercury.  Now it’s in the food chain.  It’s eaten by little fish; the little fish are eaten by bigger fish, and so on.  The more predatory, the older and the bigger the fish, the higher its concentration of methyl mercury.  Once we eat the fish, we metabolize its methyl mercury content slowly and poorly.  It’s stored in our fat, and it can take months, even a year, to clear. 

How dangerous is methyl mercury to us or to our offspring?
If adults consume high amounts of very “mercuried” fish, they can develop neurological symptoms such as numbness, pain, vision and balance problems.  Elevated blood pressure and an increased risk of heart attack have also been correlated with mercury toxicity. 

The chief concern, however, is that the fetal, infant and childhood nervous systems, as well as that of the elderly, may be especially sensitive to methyl mercury.  A recent article published in the Journal of the American Medical Association seemed, however, to give some reassurance for older adults who want to eat fish for their heart health.  Researchers examined 475 Baltimore residents, aged 50 to 70, and found that the mercury levels in their blood were not associated with the outcomes of neural behavioral test scores.  They then theorized that the growing population of aging baby boomers were not at risk for cognitive impairment if they consumed fish for its “well known benefits.” 

Our chief concern remains, however, that harm can accrue to the fetus and/or a young child as its nervous system develops.  Methyl mercury, in levels that normally would not harm an adult, can pass freely through the placenta and breast milk and destroy developing brain cells. The FDA has recommended that women who may become pregnant (remember, it can take a year to clear existing mercury levels) as well as those who are pregnant or nursing, avoid eating fish with high mercury content.  And since all children’s brains are developing and hence more vulnerable, they too should abstain.  The safety of canned tuna (the most consumed fish) and its mercury content has also caused concern.  It turns out that albacore tuna has more mercury than other forms of tuna. 

The current FDA advisory for pregnant or nursing women states the following: 

Do not eat:
Shark
Swordfish
King mackerel
Tile fish

No more than six ounces (one portion) per week:
Albacore tuna

Up to twelve ounces (two portions) a week:
A variety of fish and shellfish
Shrimp
Canned light tuna
Salmon
Pollock
Catfish

Meanwhile, you should also check local advisories about fish. If in doubt, do not eat more than six ounces (one portion) per week.

Are there other chemicals within fish that can be harmful? 
Yes.  Unfortunately, fish today have become a repository for other environmental toxins, including PCBs and organic pesticides (such as DDT).  More than a billion pounds of these chemical compounds ended up in rivers and oceans and quickly became concentrated in fish. These contaminants (many of which have been banned since the late ’70s) have stuck around for years.  PCBs and organic pesticides can have many damaging effects on our reproductive organs, skin, immune system and endocrine system, and can cause fetal malformations.  In the 1990s, DDT and its metabolites were detected in 94 percent of fish samples. 

Fish in contaminated lakes and bodies of water near industrial sites will be more likely to contain these toxins.  PCBs are often more concentrated in farm-raised fish than fish in open waters.  The highest levels have been found in anchovies, mackerel, cod and red mullet.

What about fish oil capsules?
These seem to contain few, if any, environmental toxins.  There are even DHA oil capsules made from DHA-rich microalgae (so no fish were harmed in producing this product).  Most fish oil capsules are, however, made from fish.  A one-gram capsule typically contains 300 milligrams DHA/EPA. 

The American Heart Association recommends at least one gram a day of Omega-3 fatty acids (DHA/EPA) to reduce cardiovascular risks in patients with established coronary disease, and they recommend at least two grams a day to treat high triglyceride levels.  The latter amount is hard to get through fish consumption, and it may be necessary to use supplements. 

Based on all this, what are the fish consumption recommendations for middle-aged or older men and women?
The American Heart Association states that the benefits of eating fish far outweigh the risk within the established guidelines of the FDA and Environmental Protection Agency.  Here are their recommendations:

Up to six ounces a week (one serving) fish with high mercury levels
Shark
Swordfish
Golden bass or golden snapper
King mackerel

Twelve ounces (two servings) of lower-mercury fish
Fresh or frozen tuna
Red snapper
Orange ruffy

Unlimited (the highest Omega-3 fatty acids and lowest mercury levels)
Wild salmon
Halibut
Flounder
Sole
Herring

In general, eating a variety of fish will help minimize any potentially adverse effects due to environmental pollutants. 

Dr. Reichman’s Bottom Line: Choose your fish wisely and limit your fish intake when you’re young.  Go for it after you have had your children and, as you get older, try to eat more fish.  If your diet is fish-deficient, or if you have heart disease concerns, consider adding Omega-3 supplements.

Dr. Judith Reichman, the “Today” show's medical contributor on women's health, has practiced obstetrics and gynecology for more than 20 years. You will find many answers to your questions in her latest book, "Slow Your Clock Down: The Complete Guide to a Healthy, Younger You," which is now available in paperback. It is published by William Morrow, a division of HarperCollins.

PLEASE NOTE: The information in this column should not be construed as providing specific medical advice, but rather to offer readers information to better understand their lives and health. It is not intended to provide an alternative to professional treatment or to replace the services of a physician.

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