Fish and Shellfish: How Food Affects Health

Fish and shellfish are both great sources of lean protein. Protein helps fill you up and keep you feeling satisfied, which in turn aids your weight-loss goals by making you less likely to snack on high-calorie fallback foods between meals. Protein also helps keep blood-sugar levels steady, which improves mood and protects against type 2 diabetes.

Some fish and shellfish are high in vitamins and minerals like selenium, vitamin B12, niacin, iron, and zinc. The selenium in seafood is an antioxidant that can help manage arthritis and maintain healthy skin, while vitamin B12 may help reduce the risk of cardiovascular disease and slow memory decline. Niacin is a B vitamin that may aid in cataract prevention. Iron-rich clams, oysters, and shrimp can help maintain healthy hair. The zinc in oysters and crab can also contribute to healthy hair and beautiful skin, while reducing the risk of macular degeneration.

Some shellfish are high in dietary cholesterol and therefore should be eaten in moderation by individuals with elevated LDL-cholesterol levels (if you have high cholesterol, speak with your physician about how much you should be eating).

Fish that is cured, smoked, canned, or pickled is typically high in sodium and should be avoided by people with high blood pressure. And if you suffer from migraines, be aware that these same fish varieties, which include anchovies, caviar, lox, pickled herring, and sardines, are also potential migraine triggers.

Potential Health Benefits

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.

Possible Downsides

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. 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.

Foodborn Illness

Eating contaminated shellfish can lead to foodborn illness. In fact, mollusks — such as clams, scallops, oysters, and mussels — accounted for over 45% of the seafood-related cases of foodborn 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 foodborn 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.

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

Symptoms of an allergic reaction to shellfish include:

• 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.