Eating a can of tuna isn't dangerous, but eating one every day for the rest of your life?

Haste and lack of time are two of the factors that drive the consumption of canned foods. There's no denying that opening a can of mussels, beans, or cockles is easy, quick, and very practical. If, in addition, their nutritional properties live up to expectations, as is the case, the conclusion is that including canned foods, a priori, can be a healthy option for our diet.

Now, a question related to food safety has been hovering over this eating habit for some time now, and it boils down to the question: Is it completely safe to consume canned products or is there no reason to worry?

Antía Lestido Cardama, a postdoctoral researcher with the FoodChemPack research group in the Department of Analytical Chemistry, Nutrition and Food Science at the University of Santiago de Compostela and a researcher at the University's Materials Institute (iMATUS), asserts that currently opening a can of tuna and adding it to a salad poses no health risk.

According to the expert, " food contact materials , generally understood as those intended to be in contact with food, or expected to come into contact under normal conditions of use, are manufactured in accordance with good manufacturing practices so that they do not transfer components to food in quantities that could pose a risk to human health or alter the characteristics of the food."

Specifically, regarding can coatings, legislation has evolved as more information has become available about the potential toxicity of their components. Thus, " the presence of bisphenol A, as well as its salts and bisphenol derivatives, has recently been banned in any product that may come into contact with food or beverages," notes Lara Pazos Soto, a doctoral student in the Innovation in Food Safety and Technology program, part of the FoodChemPack research group in the Department of Nutrition and Food Science at the University of Santiago de Compostela, and a member of iMATUS.

Materials for examination

In the case of cans, they are usually made of aluminum, as it is a light and ductile, yet very resistant material. Furthermore, "to increase resistance, they can contain sheets of tinplate and even metal films treated with electrolytic processes," Pazos points out.

However, to prevent possible interactions between the metal and food or beverages, coatings of different types are applied: epoxy resins, oleoresins, vinyl compounds, phenolic, acrylic, polyesters , etc. "In our research group, we have focused on the study of epoxy resins, specifically those based on bisphenol A diglycidyl ether (BADGE). These began to be used in the 1950s and have been among the most widely used until recently, due to their excellent mechanical properties," says Lestido.

Regarding the potential implications for human health, "we must ensure that the can's components can withstand the wide ranges of temperature and pressure to which they are subjected, for example, during sterilization, the acidity of the food they contain, and that they do not transfer components to the food in quantities that could harm the health of consumers," says the researcher, who maintains that "if good manufacturing practices and the limits established by the competent authorities are followed, there should be no consequences for human health."

Exposure time is key

So far, we've seen how metal containers are made from materials whose effects on human health are controlled, as experts claim. However, "even if the materials meet all the required specifications, repeated consumption of these materials could increase exposure to substances that migrate from the cans," Lestido warns. "This can affect the quality of the product and, in some cases, pose a potential risk to the consumer's health."

Furthermore, "if the product is used for purposes other than those intended, for example, heating the can directly over a fire while camping, it could accelerate the transfer of components from the coatings to the food," Pazos adds. He continues: "In the studies carried out in our laboratory, we observed that the migration of these substances depends on the type of food; for example, they tend to migrate more toward foods with a lipid nature (with fats) . Therefore, using oil or liquids to coat the cans would increase exposure to these substances."

Although, as the researchers emphasize, we are moving within the limits of a safe diet , they also warn that the amounts of contaminants vary depending on the food studied.

For example, "for components of epoxy resins used in some coatings , their presence is higher in canned foods with high lipid content, such as tuna or sardines, than in cans of tomatoes or mushrooms," says Pazos, who emphasizes that "sometimes, these contaminants are found in greater proportions in the coating liquids than in the food itself."

Furthermore, in general, "within the foods selected in our laboratory, in the specific case of BADGE-based epoxy resin coatings, canned plant foods (beans and lentils Rioja style or with vegetables) presented lower quantities of these compounds compared to fish and shellfish samples," Antía points out.

Bisphenol A (BPA), a starting product in the production of polycarbonate plastics, is a known endocrine disruptor.

On the other hand, as with canned foods, beverage cans also contain polymer coatings that come into contact with the beverages, which can have very different compositions, from soft drinks to alcoholic beverages. "The analysis of these beverages in our laboratory has also shown that they comply with current legislation for all regulated substances," the researcher assures.

Compounds and their effects

Beyond the type of food, what must be taken into account when assessing the health consequences is the type of compound that migrates (low, medium, or high toxicity, teratogenic, carcinogenic, etc.) and the frequency of consumption.

In this sense, “bisphenol A (BPA), a starting product in the production of polycarbonate plastics and epoxy resins, is a known endocrine disruptor , meaning it can affect different hormonal axes ,” Antía points out. She adds: “Studies have been conducted to understand its relationship with different metabolic diseases (obesity, diabetes) and fertility problems, although one aspect that was highlighted in 2023, when the European Food Safety Agency (EFSA) reduced the tolerable daily intake of BPA by 20,000 times , is its impact on the immune system.”

Despite the potential risk to the entire population, chemical migration does not affect everyone equally. "For example, there are population groups that are especially vulnerable, such as children, the elderly, pregnant women, etc. , because their immune systems may be compromised or their organs are still developing, and they consume more chemicals per kilogram of body weight, proportionally increasing their exposure," Pazos explains.

This risk is not only associated with the compounds in the coating of cans , as it occurs with all substances, such as medications. The dose is adjusted based on body weight and age. Thus, " children's exposure is greater , since the amount of these contaminants per body mass will be higher in children," Pazos clarifies.

In this regard, measures were taken in 2015 to reduce infant exposure to this substance by banning the presence of BPA in baby bottles. With this in mind, "in the bioaccessibility tests we conduct in our laboratory, we try to mimic the different gastric pH values ​​that the population may experience, and we observe differences," Pazos says.

Food safety agencies (such as EFSA or the Food and Drug Administration (FDA)) establish what is called a Tolerable Daily Intake (TDI) for each substance, since not all compounds have the same toxicity or behave the same way in the body.

Specifically, " when it comes to BPA , EFSA has drastically reduced its TDI in recent years due to studies showing effects on the immune and endocrine systems even at very low doses," Lestido points out. Therefore, "research in this area is important to continue providing information to authorities that will help maintain a safe food system," he adds.

As for the frequency of consumption that could put people's health at risk, too It will depend on the amount of compound that migrates , the type of food, how the can is stored, the consumer profile (children, adults, people with chronic illnesses, etc.), etc. But, in general, "normal consumption of canned foods does not represent a significant risk . In any case, authorities recommend diversifying the diet and not relying exclusively on canned products," he clarifies.

Based on the idea that consuming food preserved in metal containers is safe, we can minimize the risk we expose ourselves to by following some basic tips, such as, "for example, not heating cans directly over a fire (as can happen when camping), as this can damage the inner lining and encourage the migration of chemicals into the food," recommends Pazos.

Likewise, it does not recommend reusing topping liquids (such as oils or sauces) to dress salads, "as this could increase exposure to these migrating substances from the packaging."

"Prolonged consumption could increase cumulative exposure to certain compounds."

Furthermore, both experts advise against overindulging in canned foods, not only for food safety reasons but also for nutritional reasons. "Prolonged consumption could increase cumulative exposure to certain compounds."

Finally, "it's important to avoid consuming dented, rusted, or swollen cans ," Pazos emphasizes, "as these conditions can compromise the safety of the container, increase the risk of chemical migration, and even pose a microbiological hazard."