Tuna is one of the most common foods on the Israeli menu. It is available, convenient, requires no cooking, and for years has been considered a “safe” source of protein for those who want to eat light, fast, and healthy. But in recent years, alongside nutritional recommendations, concern has repeatedly arisen about exposure to mercury – especially in the context of tuna.
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So is it possible to eat tuna on a daily basis without worrying?
Nutritional benefits
High-quality protein – A regular can of tuna, after draining the liquids, provides on average about 25 grams of high-quality protein. This is a very high amount relative to such a simple and readily available food. For comparison, one egg contains only about 7 to 10 grams of protein.
This means that tuna makes it possible to reach a significant protein intake even in a light meal, without cooking and without special effort – an especially important advantage for people trying to maintain a healthy weight or muscle mass.
Calories
From a caloric standpoint as well, there is a clear difference between types of canned tuna. A can of tuna in oil contains about 180 to 200 calories, whereas a can of tuna in water provides only about 90 to 110 calories.
The difference does not stem from the tuna itself but from the added oil. When choosing tuna in oil, there is a clear preference for olive oil over “vegetable oil” – a general term that does not specify which oil is actually in the can or its nutritional quality.
Preservatives
Contrary to common belief, canned tuna usually does not contain preservatives. The preservation process is based on heating and sterilization rather than chemical additives, and therefore in most cases the ingredient list is relatively short and simple.
Magnesium
A can of tuna contains about 30 mg of magnesium – about 8% of the recommended daily intake – as well as about 2 to 3 mcg of vitamin B12, almost the entire daily amount required for an adult. Studies that examined the differences between fresh tuna and canned tuna found that the gaps in these components are very small, and sometimes nutritionally negligible, partly because the preservation process hardly affects these minerals and vitamins.
What about the risk of mercury?
This is where mercury comes into the picture – the main weak point of tuna.
Mercury is a heavy metal found naturally in the marine environment. In the oceans it undergoes a biological process and becomes methylmercury, a more toxic form that accumulates along the food chain. It is important to remember – predatory fish, especially those that live for many years and grow to large sizes, tend to accumulate higher levels of mercury in their bodies.
This is a critical point: Not all tuna is the same tuna. Most canned tuna is produced from a relatively small species, known as light tuna or skipjack. This is a short-lived and smaller fish, which studies have found to have significantly lower mercury levels compared to large tuna species.
In contrast, fresh tuna served in restaurants or sold at fish stalls usually comes from larger species, such as Yellowfin or Bigeye, which have been found to contain higher mercury concentrations.
Permitted amounts
Broad reviews of monitoring data, including reports by the U.S. FDA and the European Food Safety Authority (EFSA), show that in light tuna, mercury levels are significantly lower compared to large tuna species, and sometimes even lower than in other predatory fish.
Therefore, somewhat surprisingly, canned tuna is in many cases considered a safer choice in terms of mercury compared to fresh tuna.
Regarding quantities – health authorities define a tolerable weekly intake for methylmercury, calculated according to body weight. In healthy adults, consumption of one can of light tuna per day, in an amount of about 100 grams after draining, is considered in most guidelines to fall within the safety range, as long as it is not unlimited consumption and there is dietary variety.
However, in children, pregnant women, and breastfeeding women, the recommendations are stricter, and the recommended intake is limited and not daily, due to the higher sensitivity of the developing brain to mercury.
Comparison between tuna and other fish in terms of mercury
Compared to other fish, the lowest mercury levels are usually found in relatively small fish such as sardines, anchovies, and salmon, while large predatory fish such as large tuna, swordfish, and shark contain higher levels. Therefore, even for those who eat tuna regularly, it is recommended to vary and include additional fish with low mercury levels in the diet.
The bottom line is that canned tuna is not a dangerous food, nor is it a “superfood.” It is a convenient and efficient source of protein and important nutrients, which can be incorporated into a healthy diet when choosing the right type and maintaining reasonable quantities and dietary variety.
As in most areas of nutrition, the question is not whether a food is “good” or “bad,” but how much is eaten, in what context, and what else is included in the daily menu.
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