You've probably heard that eating fish is the best thing in the world because of the omega-3 fatty acids and protein it contains, but that you have to be careful because of the mercury. The truth is, fish is a cornerstone of the Mediterranean diet and provides nutrients that our bodies can't produce on their own, but not all species are the same. The problem isn't the food itself, but a heavy metal that seeps into the marine ecosystem and that some fish accumulate much more than others.
To avoid overthinking your choice every time you go to the fishmonger, it's important to understand that the key lies in the size and age of the fish. A sardine, which lives for only a few years, is not the same as a shark, which spends decades feeding on other fish. If we choose wisely, we can enjoy all the cardiovascular and brain benefits without exposing ourselves to unnecessary risks, especially during critical stages like pregnancy or childhood.
What exactly is methylmercury and how does it get into our food?
Mercury is an element found in nature, but it becomes dangerous when it enters water and bacteria transform it into methylmercury . This organic form is the most toxic because it is lipophilic, meaning it mixes well with fats and easily crosses biological barriers, such as the placenta or the blood-brain barrier.
The process occurs through the call biomagnificationImagine a chain: plankton absorbs a tiny bit of mercury; a small fish eats a lot of plankton and accumulates that mercury; and finally, a giant predator eats thousands. de peces small. That's why the animals at the top of the food pyramid end up with much higher concentrations than those at the base. In addition, mercury is not easily eliminated, but rather remains stored in the muscles and viscera of the fish.
The usual suspects: fish with high levels
When we talk about species that should be limited, we're referring primarily to large pelagic predators. Swordfish and emperor fish probably have the highest concentrations, which can reach alarming levels. Similarly, sharks (sometimes sold as dogfish or shortfin mako) and fresh bluefin tuna are long-lived fish that accumulate the metal for decades.
Caution should also be exercised with freshwater species like pike , which, being an apex predator in its environment, exhibit high levels of allergens. Generally, if the fish is very large, lives for many years, and feeds on other fish, consumption should be moderated . Interestingly, canned tuna (especially light tuna) has lower levels of allergens than fresh bluefin tuna, as younger and smaller specimens are typically used.
The safest options for everyday life
The good news is that most of the fish we consume in Spain are very safe. Sardines, anchovies, and whitebait are practically risk-free because they are small and have a short lifespan. These oily fish are veritable health powerhouses and can be eaten without restriction.
Cod is an interesting case; although it's a fairly large fish, its mercury levels are surprisingly low, making it an excellent choice for any diet. We can also rely on salmon, hake, and mollusks like mussels or clams, which , being filter feeders, tend to have minimal levels of heavy metals.
Special precautions for pregnant women and children
The nervous system of a fetus or young child is extremely sensitive. Methylmercury can act as a neurotoxin , affecting brain development and motor coordination. For this reason, the Spanish Agency for Food Safety and Nutrition (AESAN) and other health agencies are very strict: pregnant women, those planning a pregnancy, and breastfeeding mothers must completely avoid swordfish, shark, bluefin tuna, and pike.
For children, the recommendation is similar. Up to age 3, avoid large predatory fish. Between ages 3 and 12, consumption can be limited to very small amounts (about 50 grams per week), avoiding mixing several high-risk species in the same week. For the rest of the population, the general recommendation is to maintain a varied diet with 3 or 4 servings of fish per week , always prioritizing species low in mercury.
Practical tips to reduce exposure
You don't have to stop eating fish; you just need to be a little smarter when you shop. The most effective thing is to vary the species ; if you eat cod one day, go for sardines or hake the next. Don't stick to just one type of fish. Another strategy is to opt for farmed fish like salmon, since their diet is controlled and they usually have fewer contaminants than wild-caught fish.
Many people believe that cooking fish at high temperatures eliminates the metal, but this is a misconception: heat does not destroy mercury . What can help is removing the skin and visible fat, as the metal tends to concentrate in these areas. Furthermore, it's fascinating to know that fish contains selenium , a mineral that acts as a natural shield by binding to mercury and reducing its toxicity in our bodies.
Symptoms of poisoning and general risks
Mercury poisoning from eating fish is rare unless you consume large quantities of highly contaminated species, but excess mercury can take a toll on the kidneys, lungs, and cardiovascular system . The most common symptoms of high exposure include tremors, blurred vision, memory loss, unsteadiness while walking, and, in severe cases, seizures.
Fortunately, the human body can eliminate methylmercury gradually. Its half-life is estimated to be about 70 or 80 days, so if we've had an inadequate diet, reduce intake de peces large amounts cause blood levels to drop within a few months.
The wisest course of action is to avoid extreme fear and continue enjoying the sea. By choosing small, varied fish and limiting large predators, we achieve the perfect balance between nutrition and safety. The benefits of omega-3 fatty acids for the heart and brain are so potent that not eating fish at all would be riskier than eating it in moderation.
