Shellfish have been eaten all over the world for centuries.

They’re rich in lean protein, healthy fats, and minerals. Regularly eating shellfish may boost your immunity, aid weight loss, and promote brain and heart health.

However, shellfish are one of the most common food allergens, and some types may contain contaminants and heavy metals.

This article reviews different types of shellfish, their nutrition, health benefits, and possible dangers.

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As the name suggests, shellfish are animals that dwell in water and have a shell or shell-like exterior.

They can be divided into two groups: crustaceans and mollusks. Crustaceans include shrimp, crayfish, crab, and lobster, while clams, scallops, oysters, and mussels are examples of mollusks (1).

Most shellfish live in saltwater, but the name also refers to species found in freshwater.

Shellfish is available in grocery stores and restaurants all over the world, but some regions are known for certain species. For instance, lobster is a popular food in the Northeast of the United States, while shrimp is a staple in dishes from the South of the country.

Most types of shellfish are eaten steamed, baked, or fried. Some — such as oysters and clams — can be eaten raw or partially cooked. Their flavor ranges from sweet to briny, from subtle to delicate — depending on the type and cooking method.

Summary The term “shellfish” includes shrimp, crayfish, crab, lobster, clams, scallops, oysters, and mussels. Shellfish can be prepared in different ways and are eaten all over the world.

Shellfish are low in calories and rich sources of lean protein, healthy fats, and many micronutrients.

Here’s a nutrition comparison of 3-ounce (85-gram) servings of different types of shellfish ():

TypeCaloriesProteinFat
Shrimp7217 grams0.43 grams
Crayfish6514 grams0.81 grams
Crab7415 grams0.92 grams
Lobster6414 grams0.64 grams
Clams7312 grams0.82 grams
Scallops5910 grams0.42 grams
Oysters698 grams2 grams
Mussels7310 grams1.9 grams

Most of the fat in shellfish is in the form of omega-3 fatty acids, which offer a range of health benefits, such as improving brain and heart health (3, , ).

What’s more, shellfish are rich in iron, zinc, magnesium, and vitamin B12 — all of which have important roles in your body. For example, 3 ounces (85 grams) of oysters have almost 100% of the Daily Value (DV) for zinc ().

Keep in mind that shellfish are most nutritious when steamed or baked. Breaded or fried shellfish may contain additional calories, refined carbs, added salt, and other unhealthy ingredients.

Summary Shellfish are low in calories and rich in protein and omega-3 fatty acids. They also contain high amounts of certain micronutrients, including iron, zinc, magnesium, and vitamin B12.

Due to their impressive nutrient content, shellfish may be good for your waistline, brain, heart, and immune system.

May Aid Weight Loss

Shellfish are low in calories and high in lean protein and healthy fats — making them excellent foods to eat while trying to lose weight.

Protein-rich foods keep you feeling full and satisfied, which may prevent you from eating excess calories, helping you lose or maintain weight (, ).

What’s more, due to their omega-3 fatty acid content, fish may lead to greater feelings of fullness and aid weight loss more than other high-protein foods (, ).

One study in overweight adults found that those who ate more omega-3 fatty acids on a calorie-restricted diet felt significantly fuller after meals than those who ate less omega-3 on the same diet ().

May Promote Heart Health

Shellfish are loaded with nutrients that may promote heart health, including omega-3 fatty acids and vitamin B12.

Several studies have linked eating omega-3 fatty acids from fish and shellfish to a lower risk of heart disease. This is likely because omega-3s have anti-inflammatory effects (, , ).

One study in 18,244 healthy men in China found that those who ate more than 7 ounces (200 grams) of omega-3-rich shellfish per week were 59% less likely to die from a heart attack than those who ate less than 1.74 ounces (50 grams) per week ().

Furthermore, inadequate intake of vitamin B12 has been linked to high blood levels of homocysteine, a protein that can increase your risk of heart disease. Therefore, eating foods rich in vitamin B12 may protect against heart disease (, ).

Good for Your Brain

The same nutrients in shellfish that are good for your heart are also vital for brain health.

In fact, several studies have identified inadequate blood levels of vitamin B12 and omega-3 as risk factors for issues with brain development in children and with healthy brain function in adults (, , , ).

Some research also suggests that vitamin B12 and omega-3 fatty acids may enhance each other’s activities to promote brain health.

One study in 168 older adults with mild mental impairment found that B vitamins slowed the progression of brain issues in those who had higher blood levels of omega-3 fatty acids compared to those with lower levels ().

Rich in Immune-Boosting Nutrients

Some types of shellfish are loaded with immune-boosting zinc.

This mineral is necessary for developing cells that make up your body’s immune defense. It also acts as an antioxidant, protecting against damage from inflammation ().

One study in 62 healthy adults over the age of 90 found that zinc deficiency was associated with decreased activity of certain immune cells ().

Regularly eating shellfish — especially oysters, clams, mussels, lobster, and crab — may improve your zinc status and overall immune function.

Summary Shellfish are loaded with protein and healthy fats that may aid weight loss. They are also rich in nutrients — omega-3 fatty acids, vitamin B12, and zinc — that promote a healthy brain, heart, and immune system.

Even though shellfish are highly nutritious, there may be some downsides to eating them.

Heavy Metal Accumulation

Shellfish may accumulate heavy metals from their environments, such as mercury or cadmium.

Humans cannot excrete heavy metals. Over time, a build-up of these compounds in your body can lead to organ damage and other health issues ().

One study found that shellfish in some areas may contain cadmium levels that are twice the recommended daily limit for human intake. Shellfish may also contain mercury, but generally have less than larger fish (, 25).

The FDA recommends that adults eat 3–5 ounces (85–140 grams) of low-mercury fish twice a week. If the amount of shellfish you eat per week is equal to or less than that, heavy metals should not be of concern (25).

Foodborne Illness

Eating contaminated shellfish can lead to foodborne illness.

In fact, mollusks — such as clams, scallops, oysters, and mussels — accounted for over 45% of the seafood-related cases of foodborne illness in the US from 1973 to 2006 ().

Food poisoning from shellfish can result from bacteria, viruses, or parasites that are acquired from their environments ().

Pathogens flourish in raw shellfish and shellfish that are chilled incorrectly. Therefore, properly storing and cooking shellfish can be an effective way to prevent foodborne illness.

Pregnant and breastfeeding women, older adults, and people with compromised immune systems should avoid raw or improperly prepared shellfish.

Allergic Reactions

Shellfish are one of the top eight food allergens in the US (, 28).

A shellfish allergy typically develops in adulthood but can also occur in childhood.

Symptoms of an allergic reaction to shellfish include (29):

  • Vomiting and diarrhea
  • Stomach pain and cramps
  • Swelling of the throat, tongue, or lips
  • Hives
  • Shortness of breath

In some cases, people with a shellfish allergy may experience a life-threatening anaphylactic shock that needs immediate treatment (29).

Summary Shellfish may contain varying levels of heavy metals that can build up in your body and cause health issues. In addition, shellfish can cause foodborne illness and allergic reactions.

Shellfish — which can be divided into crustaceans and mollusks — are loaded with lean protein, healthy fats, and micronutrients.

They may aid weight loss, boost immunity, and promote brain and heart health. Still, shellfish may contain heavy metals and cause foodborne illness and allergic reactions.

Nevertheless, shellfish can be a nutritious and delicious addition to a balanced diet for the most healthy people.