Many people are allergic to shellfish; most of those people, however, can eat regular fish, or "finfish" as they are called in the nutritional literature. One of my dear friends, however, is allergic to "finfish" but not to shellfish, prompting me to look into the health benefits of eating these animals. After all, they sure are tasty!
It turns out that the data are somewhat mixed, but on the whole I can thankfully say: SHELLFISH ARE GOOD FOR YOU, with a few qualifications. In fact, many shellfish are EXTREMELY GOOD FOR YOU! Let's break them down by pros and cons:
1. SCALLOPS: in my literature review, it turned out that scallops were probably the healthiest shellfish out there. While they are not as high in the beneficial omega-fatty acids as some of the other shellfish, they are very high in protein, vitamins, and minerals, and relatively low in cholesterol. I would say with no reservations that if you want to eat shellfish frequently, scallops are the way to go. They are easy to grill, which is another benefit, and they freeze well.
2. CRABS AND LOBSTERS: these are a mixed bag. Believe it or not, these spiny crustaceans actually have the most beneficial omega-fatty acids of all the shellfish. So in terms of their anti-oxidant and anti-inflammatory properties, crabs and lobsters are the best shellfish choice. Some problems: First, they are overfished and numbers are declining. Second, they are high in cholesterol, which itself can contribute to heart disease. Balancing out the risk/benefits however, these are still healthier food choices than most animal meats.
3. CLAMS: not a bad food by any means. They are loaded with protein, B vitamins (who knew?) and lots of minerals. They are moderately high in cholesterol, but not as much as most animal meats. They can also be farmed, and for reasons I don't understand farmed shellfish do not seem to cause environmental degredation (the way some farmed finfish do). Of course, all filter feeding shellfish such as clams, mussels, and oysters can cause outbreaks of disease when they feed on toxic algae. But this can be avoided by cooking them.
4. MUSSELS: similar to clams, with a bit more cholesterol but also more minerals.
5. OYSTERS: similar to mussels. Naturally, they are delicious raw. They have a modest amount of cholesterol but also a modest amount of healthy omega-fatty acids. I say: eat them all you want. Yes, you could get food poisoning from them when you eat them raw, but in recent years there have been VERY few reports of food poisoning from oysters. It's fast-food beef and commercial vegetables you need to watch out for in this regard.
6. CRAWFISH (otherwise known as crayfish, crawdads, and mudbugs): nutritionally these are similar to lobsters and crabs, but lack much of the beneficial omega fatty-acids. So they are not as good for you as crabs and lobsters, and they have quite a bit of cholesterol. They are a treat when fresh, but hard to find, so most of you probably don't eat a ton of these anyway. I order them from Louisiana once a year and pig out on them for about a week, and it's fun. But I wouldn't recommend doing that every weekend.
7. SHRIMP: unfortunately, our beloved shrimp round out the bottom of the list, nutritionally. They are a great source of protein and minerals, but they are also the highest in cholesterol of all the shellfish. They do have some anti-inflammatory fatty acids in them, which might offset this a bit. But they don't have much. They are also filling, and filling foods can help reduce calorie intake for people who need to lose weight. I don't think they are a bad choice overall, and the prevalence of shrimp farming has led to less overharvesting of shrimp from the sea. My concern is that if you eat shrimp more than once every 1-2 weeks, they can increase your cholesterol numbers. Personally, I'm going to start eating less shrimp and a lot more scallops.
NOTE: I did not investigate thoroughly the "sustainability" of the above shellfish foods. However, people in the know have told me that "farmed" shellfish are both healthy and neutral to the environment. So unless you know something I don't, go for farmed shellfish and learn how to like scallops if you can.
