Clams vs oysters: calories compared

Zinc is the clearest nutrition gap, and NIH says oysters hold more per serving than any other food. In USDA survey data one raw oyster (15 g) carries about 5.9 mg, so six carry about 35 mg, near the adult upper limit of 40 mg a day, and a cup (225 g) carries 88.4 mg. For children the limit is 4 to 34 mg by age. NIH says 50 mg or more over weeks can inhibit copper absorption, and that food alone is unlikely to supply that much.

CDC says most Vibrio infections come from raw or undercooked shellfish, especially oysters. Hot sauce, lemon juice and alcohol do not kill Vibrio, and a contaminated oyster looks, smells and tastes normal. In the 1988 Shanghai hepatitis A epidemic, only 3.5% of people who fell ill had cooked their clams, against 18.1% of those who stayed well.

FDA lists raw oysters, even ones treated after harvest, among foods to avoid in pregnancy, for young children, older adults and people with weakened immunity. CDC adds liver disease, diabetes, cancer, immune-suppressing treatment and stomach acid medicines to the higher-risk list. A shrimp allergy puts both in question, because the main shellfish allergen cross-reacts between crustaceans and molluscs.

In those groups, eat them cooked. CDC advises boiling shucked oysters for at least 3 minutes.

Evidence behind this note

1. Level E NIH says oysters contain more zinc per serving than any other food. Its upper limit for zinc is 40 mg a day for adults and 4 to 34 mg for children and teens by age. Taking 50 mg or more for weeks can inhibit copper absorption, though food alone rarely supplies that much. NIH Office of Dietary Supplements, Zinc Fact Sheet for Health Professionals
2. Level E Three oysters cover the whole daily zinc reference value, and a cup of them carries more than twice the tolerable upper limit. USDA FNDDS 2021-2023 and 21 CFR 101.9(c)(8)(iv)
3. Level E CDC says most vibriosis comes from raw or undercooked shellfish, particularly oysters, and that people with liver disease, diabetes or cancer, or taking stomach acid reducers, face a higher risk of severe complications. About Vibrio Infection, US Centers for Disease Control and Prevention, People at risk
4. Level E CDC states that hot sauce, lemon juice and alcohol do not kill Vibrio in raw oysters and that a contaminated oyster does not look, smell or taste different, so neither the condiment nor an experienced palate makes a raw oyster safe. CDC, Vibrio and Oysters
5. Level C In the 1988 Shanghai hepatitis A epidemic only 3.5 percent of people who fell ill had cooked their clams, against 18.1 percent of those who stayed well. J Infect Dis, 1991
6. Level E FDA lists raw oysters, even if treated after harvest, among foods that at-risk groups should avoid, and says post-harvest treatment eliminates some naturally occurring pathogens but does not remove all pathogens that can cause illness. US FDA, Selecting and Serving Fresh and Frozen Seafood Safely
7. Level E CDC says most vibriosis comes from eating raw or undercooked shellfish, and that liver disease, cancer, diabetes, HIV, immune-suppressing therapy or stomach acid reducers raise the risk of infection and severe complications. About Vibrio Infection, US Centers for Disease Control and Prevention, People at risk
8. Level C Tropomyosin is the major shellfish allergen and it cross-reacts between crustaceans and molluscs, which is why a shrimp allergy puts clams and mussels in question rather than in the clear. Immunol Invest, 2016
9. Level E CDC says most people get a Vibrio infection by eating raw or undercooked shellfish, especially oysters. For shucked oysters it advises boiling for at least 3 minutes or frying in oil for at least 3 minutes at 375 °F. CDC, Vibrio Infection: Prevention

Written from the studies and agency guidance we hold for both foods, reviewed by the Bioma editorial system. How we verify.

Read more about these foods

• Clams: the trial used an extract, the risk is in the water
• Oysters: the zinc record holder that carries its own hazard

Rankings and guides

• Calories: what it does and what the evidence shows
• Which foods give the most protein for the fewest calories?
• Dietary fat: what it does and how much you need
• Oysters: full nutrition facts

More comparisons

• Clams vs mussels

• Clams: USDA FoodData Central, Mollusks, clam, mixed species, raw, FDC ID 174214 · all forms of clams
• Oysters: USDA FoodData Central, Mollusks, oyster, eastern, wild, raw, FDC ID 171978 · full profile · all forms of oysters

Each food is one USDA entry, chosen as it is usually eaten. Other cuts, brands and preparations differ; the links show them. % DV uses FDA Daily Values for adults. How we verify.