Crab

Crab is among the leaner protein sources from the sea — about 19g protein and 1g fat per 3oz cooked, with notable amounts of selenium, zinc, copper, and vitamin B12. The cholesterol content is moderate (a 3oz serving has around 50mg) but modern dietary guidelines no longer set a strict cholesterol cap, since dietary cholesterol has a smaller effect on blood cholesterol than once thought.

Shellfish allergy

Crustacean shellfish (crab, shrimp, lobster, crayfish) are on the FDA top-9 allergen list. The primary allergen is tropomyosin, a muscle protein that's highly cross-reactive: someone allergic to shrimp is very likely to react to crab and lobster as well. Shellfish allergy is one of the most common food allergies to persist into adulthood and is a leading cause of food-related anaphylaxis. Mollusks (clams, oysters, mussels) are a separate class — cross-reactivity is lower but not zero.

Mercury, sodium, and food safety

Crab is on the FDA "Best Choices" list — low enough in mercury that pregnant women and children can eat it 2-3 times per week. Imitation crab (surimi) is typically pollock, with the texture engineered to mimic crab, and is far cheaper and lower in actual crab — but it often contains wheat and is heavily salted. Crab is also vulnerable to histamine accumulation if not kept cold; the same scombroid-poisoning risk that applies to tuna applies here.