Fish and shellfish offer high-quality lean protein and a rich supply of beneficial omega-3 fatty acids, specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These polyunsaturated fats are instrumental in supporting heart health and general well-being. Fish also delivers important nutrients, including Vitamin D, Vitamin B12, iron, and choline. However, due to various environmental factors, these foods can also contain contaminants, necessitating clear guidelines for consumption frequency to balance nutritional gain with safety.
Standard Weekly Guidelines for Adults
Federal health organizations recommend that most healthy adults should aim to consume at least eight ounces of seafood per week. This quantity generally translates to eating fish or shellfish two to three times a week. Following this guidance helps ensure adequate intake of omega-3 fatty acids.
A standard serving size for adults is typically defined as four ounces of cooked fish. Therefore, the weekly recommendation of eight to twelve ounces is equivalent to two or three such servings. This frequency is designed to provide the heart-protective and cognitive benefits of seafood without introducing an undue level of contaminants. The emphasis is placed on choosing a variety of options to diversify nutrient intake.
The Primary Concern: Mercury Contamination
The main environmental factor influencing consumption limits is the presence of mercury, specifically its organic form, methylmercury. This compound forms when elemental mercury, released into the environment through both natural processes and industrial pollution, is methylated by bacteria in aquatic sediments. Fish and shellfish absorb this methylmercury from the water as it passes over their gills and through their diet.
Methylmercury then undergoes a process called biomagnification as it moves up the aquatic food chain. Larger, longer-lived predatory fish consume many smaller fish over their lifetime. This results in the highest concentrations of methylmercury accumulating in the largest predators.
For adults, excessive exposure to methylmercury primarily affects the nervous system. Symptoms associated with chronic high-level exposure can include neurological abnormalities such as paresthesia (numbness or tingling in the extremities). Other reported effects involve sensory disturbances, including constriction of visual fields, hearing impairment, and poor motor coordination.
Choosing Fish Based on Mercury Levels
To safely adhere to consumption guidelines, fish are categorized based on their typical methylmercury concentration. Selecting options from the “Best Choices” category allows for the consumption of two to three servings per week. These low-mercury options include:
- Salmon
- Shrimp
- Tilapia
- Cod
- Catfish
- Canned light tuna
Conversely, some fish species are classified as “Choices to Avoid” due to their exceptionally high mercury levels. This group includes King Mackerel, Swordfish, Shark, and Tilefish from the Gulf of Mexico.
There are also “Good Choices” that can be eaten once per week, which often have slightly higher mercury levels than the best choices. For example, Albacore (“white”) tuna has a higher methylmercury content than canned light tuna and should be limited to one serving (six ounces) per week.
Specific Advice for Pregnant Women and Young Children
The guidelines are stricter for women who are pregnant or breastfeeding, as well as for young children, because the developing brain and nervous system are particularly vulnerable to methylmercury. Exposure during the prenatal period can lead to neurological damage and developmental delays in the child. Therefore, these vulnerable populations must strictly adhere to consuming only fish from the lower-mercury categories.
Women who are pregnant or nursing should consume between eight and twelve ounces of low-mercury fish each week. This intake is encouraged because the omega-3 fatty acids in fish are demonstrably beneficial for the baby’s cognitive development. The fish classified as “Choices to Avoid” must be completely excluded from the diets of pregnant women and young children.
For children, serving sizes are smaller and scaled according to age and caloric needs. Children should also be served two servings per week from the “Best Choices” list to support proper growth and brain development. On average, serving sizes are:
- Ages one to three years: about one ounce.
- Ages four to seven years: two ounces.
- Ages eight to ten years: three ounces.