Contents
What it is
The oyster is a bivalve that lives cemented to rock or to farming lines. It stays in one place all its life, filtering the water around it, which means it reflects the state of that water directly — and that is why raw oysters are regulated so strictly. Oysters grown in cold water build up glycogen and taste richest in winter; during the summer spawning season the flavour falls off and the risk of food poisoning rises. They are eaten raw, but because of norovirus and vibrio, anyone with a weakened immune system is safer eating them cooked.
Scientific name Crassostrea gigas
Oysters are not called "milk of the sea" only for their protein. Their zinc content is on a different scale from other foods.
16.6 mg per 100 g. Beef sits at 4–5 mg and pumpkin seeds at about 7 mg — an order-of-magnitude difference. Zinc is directly involved in immune cell function, wound healing, taste, and male reproductive function.
Key benefits
- Nutrition data
Zinc is required for immunity and wound healing
Zinc is essential to T-cell maturation and function, and deficiency leaves you vulnerable to infection. The trials showing shorter colds with early zinc supplementation rest on this same role.
- Moderate evidence
The link to male reproductive function is real
The folklore about oysters has a compositional basis. Zinc participates in sperm production and testosterone metabolism, and these decline in zinc deficiency. That does not mean more helps someone already replete.[1]
- Nutrition data
Overwhelming in vitamin B12
100 g provides more than six times the daily requirement. B12 is needed for red cell formation and nerve function and is nearly absent from plant foods, making oysters valuable for anyone at risk of deficiency.
- Nutrition data
Iron in the heme form
5.1 mg per 100 g, and as heme iron it absorbs well — far less hindered by oxalate or phytate than plant-source iron.
How to eat it well
- For raw oysters, buy only those labelled for raw consumption. Handling standards differ from those meant for cooking.
- The habit of squeezing lemon makes sense nutritionally too: vitamin C aids iron absorption.
- Cooking them through eliminates norovirus risk. Heat all the way to the centre.
- Winter is the season. Summer oysters, during spawning, are worse on both flavour and safety.
- Zinc intake above 40 mg a day is not advisable, so skip zinc supplements on days you eat a lot of oysters.
How to read the grades
Each benefit carries a label showing how far research on people supports it. Grades differ between items even within the same ingredient.
- Nutrition data
- A fact verifiable from food composition databases or health authorities. This is a different kind of statement from a clinical effect.
- Strong evidence
- Consistently confirmed across randomised controlled trials or meta-analyses.
- Moderate evidence
- Human studies exist, but effect sizes are small or results are mixed.
- Early research
- Cell or animal work, or small preliminary studies.
- Not established
- Commonly claimed, but not confirmed in studies on people.
What to watch out for
- They are a major route for norovirus and Vibrio infection. People who are immunocompromised, pregnant, or have liver disease should avoid raw oysters.
- Excess zinc causes copper deficiency. Avoid sustained high intakes.
- With gout, account for the purine content.
- Avoid entirely with shellfish or mollusc allergy.
- It is worth checking the harvest area for heavy metal contamination.
Nutrition
Per 100 g of raw oyster — roughly five or six medium oysters. Grilling or steaming drives off water, so the same weight cooked shows higher figures, and canned oysters bring their own liquid and sodium.
- Calories
- 68 kcal3%
- Protein
- 7.1 g14%
- Fat
- 2.5 g3%
- Carbohydrates
- 3.9 g1%
- Zinc
- 16.6 mg151%
- Vitamin B12
- 16 µg667%
- Iron
- 5.1 mg28%
- Selenium
- 63 µg115%
- Copper
- 1.6 mg178%
Percentages are of the US FDA Daily Value for adults and children 4 and over. National reference intakes differ by sex and age.
Calculate this alongside other ingredients →
Key nutrients
Sources
The databases and health authorities this article's nutrition figures and health statements draw on.
- 1The Effect of Nutrients and Dietary Supplements on Sperm Quality Parameters: A Systematic Review and Meta-Analysis of Randomized Clinical TrialsMeta-analysisSalas-Huetos A, et al. Adv Nutr 2018PMID 30462179
- 2USDA FoodData CentralFood composition database
- 3NIH Office of Dietary SupplementsHealth authority
- 4PubMedResearch literature
