Tuna is frequently presented raw or lightly cooked in various dining establishments and sushi bars. This particular fish is not only delicious but also exceptionally nutritious, offering a plethora of health benefits. However, many may question the safety of consuming it in its raw form.

This article delves into the potential risks associated with eating raw tuna and provides guidance on how to enjoy this delicacy safely.

Types and Nutritional Benefits of Tuna

Tuna, a popular saltwater fish, is enjoyed in various cuisines around the globe, from Australian fish and chips to Indian seafood curries. This versatile fish comes in several varieties, including skipjack, albacore (known as 'dhoma' in India), yellowfin, bluefin, and bigeye, each differing in size, color, and flavor profile.

Notably, tuna is a highly nutritious and lean source of protein. For instance, 100 grams of albacore tuna provide you with:

  • Calories: 124
  • Carbohydrates: 0 grams
  • Protein: 27 grams
  • Fat: 3 grams

The majority of the fat found in tuna consists of omega-3 fatty acids, which are essential for maintaining heart and brain health, and may also aid in reducing inflammation. Furthermore, tuna is rich in iron, potassium, and B vitamins. It stands out as an excellent source of selenium, a trace mineral that functions as an antioxidant and may lower the risk of heart disease and other chronic ailments.

When it comes to preparation, canned tuna is cooked during processing, whereas fresh tuna is often enjoyed rare or raw, contributing to its popularity in dishes like sushi and sashimi. These traditional Japanese delicacies combine raw fish with rice, vegetables, and seaweed, showcasing the fish's delicate flavors. Tuna, whether served raw or lightly cooked, remains a lean protein packed with omega-3 fatty acids, along with an array of vitamins and minerals. It is conveniently available in both fresh and canned forms, catering to diverse culinary preferences.

Potential for Parasitic Infections

While tuna is renowned for its rich nutritional profile, consuming it in its raw form can present certain health risks. This is primarily due to the possibility that raw fish, including tuna, may harbor parasites such as Opisthorchiidae and Anisakidae, which can induce various illnesses in humans. Depending on the species, these parasites can lead to foodborne diseases characterized by gastrointestinal disturbances, including diarrhea, vomiting, fever, and other related symptoms. Research has indicated that a staggering 64% of young Pacific bluefin tuna samples sourced from Japanese waters were found to be infected with Kudoa hexapunctata, a parasite associated with diarrhea in humans.

In a similar vein, another study revealed that both bluefin and yellowfin tuna from the Pacific Ocean tested positive for various parasites from the Kudoa family, known for causing food poisoning. Additionally, findings from a study conducted on tuna from the Iranian coastline showed that an alarming 89% of samples were infected with parasites capable of attaching to the human stomach and intestines, resulting in anisakiasis — a condition characterized by bloody stools, vomiting, and abdominal pain.

The likelihood of encountering parasitic infections from tuna is largely influenced by the geographical location where the fish is caught. Furthermore, the methods of handling and preparation play a crucial role in determining the transmission of these parasites. Fortunately, most parasites can be effectively eradicated through adequate cooking or freezing techniques. As a result, the risk of parasitic infections linked to raw tuna can be significantly mitigated by ensuring proper handling practices are followed.

Potential Mercury Levels in Tuna

Certain species of tuna are known to contain elevated levels of mercury, a toxic heavy metal that enters our oceans primarily due to environmental pollution. This harmful substance accumulates in tuna over time, particularly because these fish occupy a higher position in the marine food chain, preying on smaller fish that may already harbor varying concentrations of mercury. Consequently, larger species of tuna such as albacore, yellowfin, bluefin (kuro-maguro), and bigeye (mebachi) are frequently associated with higher mercury levels. These varieties are commonly used in raw preparations like sushi and sashimi.

Remarkably, a study analyzing 100 raw tuna sushi samples from northeastern Canada revealed that the average mercury concentration surpassed the daily consumption limits advised in both Canada and Japan. This finding raises concerns regarding the implications of consuming too much raw tuna.

Eating excessive amounts of raw tuna can lead to elevated mercury levels in the body, resulting in severe health risks, including potential damage to the brain and heart. It’s particularly important to be cautious with certain tuna varieties, especially bigeye and bluefin, as they may have significantly high mercury content. Prolonged exposure to high mercury levels poses serious threats to one's health, affecting both neurological and cardiovascular functions.

Who Should Avoid Raw Tuna?

Individuals such as pregnant and breastfeeding women, children, older adults, and those with weakened immune systems—like patients undergoing cancer treatment—are advised against consuming raw tuna. This caution is primarily due to their heightened vulnerability to foodborne illnesses, which can arise from parasites commonly found in raw or undercooked tuna.

Moreover, pregnant and breastfeeding women, along with young children, are particularly at risk from mercury exposure, necessitating a significant reduction or total avoidance of both raw and cooked tuna. Nonetheless, it's prudent for all adults to be mindful of tuna intake, as many varieties contain mercury levels that exceed the daily limits recommended by health organizations in Australia, Canada, Japan, and other nations. Both raw and cooked forms of tuna should be consumed sparingly. Nevertheless, adults are encouraged to eat between 85 to 140 grams (approximately 3–5 ounces) of fish 2 to 3 times each week to ensure adequate intake of omega-3 fatty acids. To fulfill this guideline, it's beneficial to choose fish that are lower in mercury, such as salmon, cod, or crab, while reserving tuna for occasional enjoyment.

In summary, pregnant and breastfeeding women, children, older adults, and those with weakened immune systems should be particularly cautious and avoid raw tuna to mitigate the risks associated with parasitic infections and mercury exposure.

How to Enjoy Raw Tuna Safely

While cooking tuna is the most effective method to eliminate parasites and reduce the risk of foodborne illnesses, it is entirely possible to consume raw tuna safely.

The Food and Drug Administration (FDA) outlines several freezing techniques that can effectively eradicate parasites:

  • Freezing at -4? (-20?) or lower for a duration of 7 days.
  • Freezing at -31°F (-35°C) or lower until completely solid, then maintaining that temperature for 15 hours.
  • Freezing at -31°F (-35°C) until solid, then storing at -4°F (-20°C) or below for 24 hours.

It’s essential to thaw frozen raw tuna in the refrigerator prior to enjoying it. By adhering to these guidelines, the majority of parasites are likely to be eliminated; however, a minimal risk may still exist that not all parasites have been eradicated. Most sushi restaurants and establishments that serve raw tuna comply with the FDA’s freezing recommendations. If you have any concerns regarding the preparation of your raw tuna, don’t hesitate to inquire further and ensure that you only consume raw tuna from well-established and reputable restaurants.

For those intending to create a raw tuna dish at home, it’s advisable to seek out a knowledgeable fishmonger who can provide information about the source and handling of their fish. When prepared following FDA guidelines, raw tuna can generally be enjoyed safely, making it a delightful addition to your culinary repertoire.

Conclusion

When handled properly and frozen to remove parasites, raw tuna can be considered safe for consumption. This fish is exceptionally nutritious; however, some species contain elevated levels of mercury, making it essential to enjoy it in moderation. Vulnerable groups such as pregnant women, breastfeeding mothers, children, seniors, and individuals with weakened immune systems should refrain from consuming raw tuna.