Crab itself is a great lean protein source that is extremely low in fat and carbs. There are several different kinds (blue crab, Dungeness crab, etc.), but in general, a 3-oz cooked serving has around 80 calories, 20 gms of protein, 1 gm of fat, and less than 1 gm of carbohydrate. It also provides almost 25% of the daily value for zinc, which is linked to good immune function, protection against cardiovascular disease, and fertility. It contains about 10% of the daily value for calcium, greater than 100% of the daily value for Vitamin B12, and small amounts of many of the other B vitamins. It’s also low in mercury.
Crabs are generally covered with a thick exoskeleton, composed primarily of highly mineralized chitin, and armed with a single pair of chelae (claws). Crabs are found in all of the world’s oceans, while many crabs live in fresh water and on land, particularly in tropical regions. Crabs vary in size from the pea crab, a few millimetres wide, to the Japanese spider crab, with a leg span of up to 4 metres (13 ft).