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All About Shellfish
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All About Shellfish

Are you working to keep your cholesterol level down? Have you stopped eating lobster, crab, and the like because you thought shellfish was loaded with cholesterol? Well, think again. Throw another shrimp on the barbecue and read on because shellfish once blacklisted by the cholesterol police have been given a reprieve.

Doesn't Shellfish Have a Ton of Cholesterol?

Actually, no. Shellfish's cholesterol level is not as health threatening as once believed.

There are a few reasons why shellfish may have a bad reputation when it comes to cholesterol. First, shellfish contain a variety of sterols a group of chemical compounds that includes cholesterol. Previously, scientists could not distinguish among the different sterols and all were labeled as cholesterol. As a result, the amount of cholesterol in shellfish was overestimated. In reality, shellfish contain less cholesterol than meat or poultry.

Not Much Fat, Though

Another factor that worked against shellfish was the thought that dietary cholesterol raised blood cholesterol levels. Because shellfish does contain cholesterol, it was considered "bad" for you. Now we know that dietary cholesterol is only a minor contributor to blood cholesterol levels: total calorie intake and the quantity and type of fat, such as trans fat and saturated fat, in the diet are far more important. Fortunately, the fats in shellfish are in the “healthy” category.

Bad Company

The company that shellfish keep, however, can be a problem. Shellfish are often served with melted butter or a mayonnaise-based tartar sauce. And shellfish are frequently battered and deep fried. Both actions can turn a low fat dish into a high fat bomb by increasing the total fat and the saturated fat. Instead, try steaming shellfish and serving with lemon and spices.

What Makes a Fish a Shellfish?

It's as simple as it sounds—shellfish are sea creatures that have a shell of some kind. There are two basic categories:

Crustaceans—elongated bodies with jointed, soft shells; these include crabs, crayfish, lobster, and shrimp.

Mollusks—soft bodies covered by a shell of one or more pieces. Mollusks are divided into three categories:

  • Univalves—a single shell and a single muscle; includes abalone and snail.
  • Bivalves—two shells hinged together by a strong muscle; includes clam, scallop, mussel, and oyster.
  • Cephalopods—tentacles attached to the head and an ink sac; includes octopus and squid.

Shellfish Allergies

Shellfish are one of the most common allergens, and the allergy is rarely outgrown. Reactions usually appear within two hours after ingesting shellfish, inhaling cooking vapors, or handling shellfish, but can be delayed as long as 24 hours. Common symptoms include:

  • Nasal congestion
  • Hives
  • Itching
  • Swelling
  • Heartburn
  • Wheezing
  • Shortness of breath
  • Nausea
  • Upset stomach
  • Cramps
  • Gas
  • Diarrhea
  • Light-headedness
  • Fainting
  • Swelling around mouth

The key to living with a shellfish allergy is to avoid all foods or products that contain shellfish. Make sure you read a product's label because shellfish may be a minor ingredient.

Shellfish Poisoning

Food poisoning can occur after eating tainted shellfish; clams and mussels are the types most frequently at fault. Symptoms can occur in as little as 10 minutes after ingestion and begin with a tingling and numbness around the lips. Staggering, giddiness, and muscular incoordination may appear and speech is often incoherent. In severe cases, shellfish poisoning may result in seizures, coma, or death. If you suspect shellfish poisoning, seek medical attention immediately.

The sickness is most often caused by a toxin that shellfish ingest along with the plankton they eat during certain times of the year. Unlike bacteria that can cause food poisoning, these toxins cannot be destroyed through cooking. To protect yourself, always buy from reputable seafood sellers.

What About Mercury?

Recently, considerable concern has grown about mercury levels in fish. This is a problem with some shellfish too. Although shellfish do not usually approach the mercury levels of the worst fish offenders (such as swordfish and shark), lobster has as much mercury as canned white tuna, and scallops and crab have about a sixth as much. Mussels vary in mercury content depending on their origin. Shrimp and oysters have little to no mercury content.

Guidelines for Cooking Shellfish

To cook raw shellfish, shucked or in the shell, follow these basic guidelines. Note that the cooking times are short because shellfish may become tough and dry when overcooked.

Raw shrimp—turn pink and firm when cooked. Depending on the size, it takes 3 to 5 minutes to boil or steam one pound of medium-sized shrimp in the shell.

Crab legs—can be cut at the joints and boiled or steamed. Depending on the amount, boiling crab legs takes about 2-3 minutes and steaming will take about five minutes or until thoroughly heated.

Shucked shellfish (clams, mussels, and oysters without shells)—become plump and opaque when cooked thoroughly and the edges of the oysters start to curl. The Food and Drug Administration (FDA) suggests boiling shucked oysters for three minutes, frying them in oil at 375° F for 10 minutes, or baking them for 10 minutes at 450° F.

Clams, mussels, and oysters in the shell—will open when cooked. The FDA suggests steaming oysters for 4 to 9 minutes or boiling them for 3 to 5 minutes after they open.

Scallops—turn milky white or opaque and firm. Depending on size, scallops take 3 to 4 minutes to cook thoroughly.

Boiled lobster—turns bright red. Allow 5 to 6 minutes per lobster. Drop lobster into boiling water and start your timer when the water returns to a full boil.

Nutritional Info

Shellfish Nutritional Information
Item Serving
size
Calo-
ries
Fat
(g)
Satu-
rated-
fat
(g)
Cho-
les-
terol
(mg)
Pro-
tein
(g)
Potas-
sium
(mg)
So-
dium
(mg)
Abalone 3 oz
(85 g)
89.50.5072.514.5213256
Clams 20 small
(180 g)
7410341331456
Crab,
Alaskan
King
1 leg
(172 g)
144.5107231.53511438
Crab,
Dungeness
1 crab
(163 g)
1401.509628.5577481
Crayfish 8 pieces
(27 g)
19.50.502947117
Lobster 1 lobster
(150 g)
1351.50.5142.528413444
Mussels 1 large
(20 g)
170.505.52.56457
Oysters,
Eastern
6 med
(84 g)
49.51.50.5214.5104150
Oysters,
Pacific
1 med
(50 g)
40.510.5254.58453
Scallops 2 large
(30 g)
26.5001059749
Shrimp 4 large
(28 g)
29.50.5042.55.55242
Squid 1 oz
(28.5 g)
260.50664.57013

RESOURCES:

American Dietetic Association
http://www.eatright.org

FoodSafety.gov
http://www.foodsafety.gov/~fsg/seafood.html

CANADIAN RESOURCES:

Canadian Council on Food and Nutrition http://www.dietitians.ca/
www.ccfn.ca

Dietitians of Canada
http://www.dietitians.ca/

References

Mercury levels in commercial fish and shellfish. Center for Food Safety and Applied Nutrition website. Available at: http://www.cfsan.fda.gov/~frf/sea-mehg.html.

Questions and answers on seafood. Center for Food Safety and Applied Nutrition website. Available at: http://www.cfsan.fda.gov/~dms/qa-topse.html.



Last reviewed January 2008 by Dianne Scheinberg MS, RD, LDN

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.


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