Is Shrimp Safe?

Michael Greger (0:00)

We have lots of choices to make about our diet. Add to that doing the right thing when it comes to treating a chronic disease, fighting a virus, or losing weight, and suddenly our nutrition choices can seem almost overwhelming. Well, I'm here to help. Welcome to the Nutrition Facts Podcast. I'm your host, Dr. Michael Greger.

Did you know that eating just a single shrimp could potentially exceed the safety limit of banned pesticides and chemicals? Here is our first story.

Over a decade ago, farmed shrimp overtook wild-caught, such that by 2016, two-thirds of global shrimp production was farmed. The main potential food safety hazards of shrimp farming are infectious disease, chemical contamination, and veterinary drug residues. In terms of margarine, shrimp is the second leading source, but it's still far behind tuna. In terms of banned pesticides, flame retardants, and polycyclic aromatic hydrocarbons, there are some significant concerns regarding human health risks associated with shrimp consumption. Safety limits were exceeded for banned pesticides chlordane, DDT, heptachloroaldrin, dealdrin, and endosulfan. Now, this was based on worst-case scenario values, but on the other hand, based on just eating 3.5 grams of shrimp a day, which is like a single shrimp, or one serving of shrimp every two weeks or so. Eating just one shrimp could give you as much as 50 times more DDT than is considered safe. Same with flame retardant chemicals, the same with naphthalene and benzopyrene. For PFAS forever chemicals, eating the highest levels of the most contaminated shrimp could pose a health risk, which comes out to be about a serving a day. Shrimp can also be a substantial source of carcinogenic heterocyclic amines, which is typically seen in dry, heat-cooked chicken, like baked, grilled, fried, or broiled. Levels for shrimp were in the 10 to 50 range, which is what you start to see with chicken grilled at over 400 degrees Fahrenheit. Note that steaming, or presumably boiling, or other moist cooking methods are the safest ways to cook meat.

Another issue with shrimp is foodborne illness, even with pre-cooked ready-to-eat shrimp, which have been found to be an international vehicle of antibiotic-resistant bacteria. As shrimp farming has gotten more intensive, there's an increased occurrence of disease problems as a direct result of the higher stocking densities that shrimp farms, causing stress-initiated disease and then rapid transmission of infectious diseases. And along with more disease comes more use of antibiotics and disinfectant chemicals to keep the animals from dying prematurely. In India, where most of the shrimp eaten in the United States comes from, 90% of the bacteria tested were resistant to three or more classes of antibiotics. Thus, shrimp can serve as delivery vehicles of anticobeial resistance to pathogenic bacteria to consumers and from country to country. Thirteen brands of ready-to-eat shrimp from four countries of origin were obtained from local grocery stores in the US. And 80% of the bacterial species picked up were antibiotic resistant, and that included numerous resistant human pathogens such as E coli and salmonella. Food-borne pathogens were found in every single sample tested, and most of those contained multiple pathogens. Ready-to-eat shrimp are sold with instructions to just thaw before serving, which may result in consumer exposure to antibiotic-resistant bacteria.

Enterococci are used as markers of fecal contamination of food products. At a retail level, about 85% of ground beef and turkey are contaminated with fecal bacteria. About half of chicken and a third of pork. Sampling more than 700 shrimp at grocery outlets in eight states across the United States, researchers found that approximately two-thirds of the shrimp samples were contaminated with fecal bacteria.

In terms of antimicrobial resistance in US retail seafood, shrimp had the highest odds of being contaminated, and the risk was about twice as high in farm-raised shrimp compared to wild-caught shrimp. A small percentage were even resistant to a carbapenem antibiotic, which is considered an antibiotic of last resort in the hospital. We used to call it Gorilla Cillin. It's also been found in Canadian shrimp, linked to a farming operation in India, our number one source of shrimp imports, and other straits back to Vietnam and Ecuador, other major shrimp importers into the United States. So shrimp farms may be a key reservoir of antibiotic-resistant genes, which may pose a significant threat to public health. When we consume shrimp, we may also be consuming those antibiotic-resistant genes, which can be passed along to human pathogens in our own body. Resistance genes have been detected in shrimp products destined for human consumption, but what about the antibiotics themselves? Are there residues of antibiotic drugs left in shrimp at a retail level? That's what I'll cover next.

About 90% of shrimp consumed in the United States is imported. Because much important seafood is form-raised in confined conditions, drugs are used to prevent or treat disease and increase survival rates, and residues of some of these drugs can cause cancer or allergic reactions or contribute to antibiotic resistance. Among different kinds of seafood, shrimp have had the highest frequency of veterinary drug violations, primarily from nitrofurans and chloramphenicol. The United States banned chloramphenicol 35 years ago due to a link with a rare and often fatal disease called aplastic anemia. Nitrofurans are also dangerous because they are potential cancer-causing properties, so their use in animals produced for human consumption is similarly banned in Europe and the United States. For something as potentially dangerous as chloramphenicol, governments around the world have established zero-tolerance policies, which means that no residues in food are permissible. However, traces of chloramphenicol have been detected in shrimp. Unlike most of the animals we eat, who have multiple organs for drug excretion, shrimp possess only one, which may allow more antibiotics to build up in them, but you don't know until you put it to the test. There have been four studies published on the presence of banned drugs in retail US shrimp. One found that 92% of imported farm-raised shrimp tested positive for at least one drug that is banned for use in the United States. Another of just six shrimp from stores in Arizona and California found drugs in two of them. The third tested dozens purchased in Louisiana from many of our main shrimp importers, and 70% tested positive for the zero-tolerance carcinogenic nitrofurantoin.