Swordfish (Xiphias gladius), a formidable predatory fish, is enjoyed by seafood lovers across the globe. This impressive fish is easily recognized by its unique, sword-like bill, a feature that inspired its name. Notably, it ranks among the fastest fish in our oceans, showcasing both speed and agility. When it comes to nutrition, swordfish boasts a remarkable profile, offering a variety of health benefits that can enhance overall well-being. However, it is essential to exercise caution, as consuming this fish in excessive quantities or too frequently can lead to mercury accumulation in the body, posing health risks.

This article explores the health implications of swordfish consumption, highlighting both its advantages and potential drawbacks, as well as guidelines on safe consumption levels.

Nutritional Benefits of Swordfish

Swordfish stands out as a powerhouse of essential nutrients that are vital for maintaining good health. These essential nutrients are not synthesized by the body and must be obtained through dietary sources.

A typical serving size of 100 grams of cooked swordfish offers:

  • Calories: 173
  • Protein: 25 grams
  • Fat: 7.8 grams
  • Carbohydrates: 0 grams
  • Selenium: 125% of the Daily Value (DV)
  • Vitamin D: 85% of the DV
  • Potassium: 11% of the DV
  • Magnesium: 8% of the DV

This fish is particularly abundant in selenium, a vital trace mineral that plays a crucial role in various bodily functions, including thyroid regulation, bone metabolism, immune support, cardiovascular health, and male reproductive health. Moreover, swordfish serves as an excellent source of vitamin D, which is essential for maintaining strong bones and has demonstrated positive effects on immunity, heart function, and respiratory health conditions like asthma.

In addition to its vitamin content, swordfish is classified as a fatty fish, rich in omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Both EPA and DHA are essential fats recognized for their protective benefits against heart disease and inflammation, as well as their ability to enhance cognitive function. A 100-gram serving offers approximately 900 mg of combined EPA and DHA. The 2015-2020 Dietary Guidelines for Australians recommend a daily intake of around 250 mg, making swordfish an exceptionally rich source.

Advantages of Consuming Swordfish

Swordfish offers numerous health advantages, primarily attributed to its abundant content of omega-3 fatty acids, selenium, and vitamin D.

Potential to Lower Heart Disease Risk Factors

Elevated blood pressure and high cholesterol levels are significant contributors to heart disease. The omega-3 fatty acids present in swordfish may have a beneficial effect on blood pressure and cholesterol, particularly among individuals with existing heart conditions. Notably, these fatty acids do not seem to interfere with prescribed medications.

Studies indicate that EPA and DHA, types of omega-3s, can help lower blood pressure by reducing heart rate and enhancing the function and elasticity of blood vessels. Moreover, these fatty acids may contribute to lowering blood triglycerides by about 20-30% and can assist in preventing the formation of blood clots that can obstruct arteries. However, it's worth noting that they might elevate LDL (bad) cholesterol levels, which is another risk factor for heart disease.

In addition, the vitamin D content in swordfish may help reduce blood pressure and the likelihood of heart attacks. A particular study found that individuals with a deficiency in vitamin D faced a 60% higher risk of heart disease. Research suggests that vitamin D supplementation might lower systolic blood pressure (the upper figure in blood pressure readings) by 2-6 mm Hg, likely through its interactions with various body systems, including the kidneys and endocrine system.

May Help Lower Cancer Risk

Swordfish may offer protection against cancer, thanks to its omega-3, vitamin D, and selenium components.

Inflammation is a key factor contributing to cancer, and both omega-3s and vitamin D possess anti-inflammatory properties. Research implies that these nutrients can help guard against colorectal cancer. These nutrients may inhibit the replication of cancerous cells and promote their death. Furthermore, vitamin D may help impede the formation of new blood vessels that nourish these cells.

Omega-3s also assist in preventing the spread of cancer, a process known as metastasis. While animal studies and some human research show a reduction in colorectal tumor size, results in human studies have been inconsistent. Selenium acts as a potent antioxidant that combats the damaging effects of excess free radicals in the body, potentially offering protective benefits against liver, prostate, breast, and lung cancers. Additionally, selenium supplementation may improve the quality of life for individuals undergoing radiotherapy and mitigate the side effects associated with such treatments. While these findings are promising, it is crucial to understand that they focus on specific nutrients rather than the direct effects of swordfish consumption itself. Therefore, further research is necessary to explore the specific impacts of swordfish.

Promotes Bone Health

The vitamin D and selenium found in swordfish could significantly enhance bone health.

Vitamin D's primary function is to facilitate calcium absorption in the gut, and it plays a vital role in bone formation. A deficiency in vitamin D is associated with bone loss and an increased risk of falls and fractures. Though selenium may not be as widely recognized as vitamin D, it also contributes to bone health by regulating bone metabolism, a process governed by bone cells known as osteoblasts and osteoclasts.

During bone remodeling, osteoblasts create new bone tissue, while osteoclasts break down bone to release minerals into the bloodstream. Selenium helps maintain a healthy balance by inhibiting osteoclast activity, thereby preventing brittle bones. Research has shown that low levels of selenium in the blood correlate with a heightened risk of low bone mineral density and bone diseases. 

Potential Downsides

Incorporating swordfish (sura) into your diet may offer various advantages; however, it comes with a significant concern — its elevated levels of mercury. This toxic heavy metal primarily originates from industrial waste and the burning of coal. Over time, mercury emissions find their way into lakes and oceans, often due to precipitation.

Initially, small aquatic organisms absorb mercury, which accumulates in larger predators through their consumption. Consequently, this process allows mercury to ascend the food chain, leading to higher concentrations in larger, longer-living species like swordfish. As a potent neurotoxin, mercury can adversely affect brain function. Individuals who consume excessive amounts of predatory fish — exceeding five servings per week — face heightened risks. Interestingly, mercury exposure may even counteract the heart health benefits typically associated with omega-3 fatty acids.

This concern is particularly crucial for the developing central nervous systems of infants. Studies indicate that mercury can traverse the placenta or be transferred to babies through breast milk, posing significant risks. Therefore, it is strongly advised that pregnant and breastfeeding individuals refrain from consuming swordfish.

How to Prepare Swordfish

Swordfish, known for its meaty texture and subtly sweet flavor, can be prepared with or without a marinade. Many culinary enthusiasts opt for oil-based marinades infused with fresh herbs to enhance its taste. Typically, swordfish is sliced into 1-inch (2.5-cm) fillets and cooked similarly to a rare beef steak, making it a delightful option for grilling. Although the skin is often removed due to its rubbery feel, leaving it on during the cooking process can help retain moisture, resulting in a juicier final dish.

In addition to grilling, other popular cooking techniques for swordfish include boiling and stewing, which take advantage of its firm texture that resists flaking or breaking apart during cooking. Although deep-frying is not a common method for preparing swordfish, it remains a viable option. However, it is important to note that deep-frying can lead to the formation of trans fatty acids (TFA), which may elevate the risks associated with heart disease.

When selecting swordfish, ensure that the fillets are free from any discoloration, dark edges, or signs of drying. Fresh swordfish should possess a clean scent, devoid of any fishy or rancid odors. Raw swordfish can be safely refrigerated for up to 2 days before cooking, or it can be frozen for as long as 3 months. Once cooked, swordfish can be stored in the refrigerator for up to 4 days or in the freezer for up to 6 months.

The Bottom Line

Swordfish, known for its rich flavor and meaty texture, is a highly sought-after fish that boasts an impressive nutrient profile, including omega-3 fatty acids, selenium, and vitamin D. These nutrients provide a multitude of health benefits, contributing positively to both heart and bone health, while also potentially lowering the risk of certain cancers.

Nonetheless, it is essential to be cautious, as swordfish contains elevated levels of mercury, a harmful trace metal that can adversely affect brain health, particularly during the critical developmental stages of infants. Consequently, individuals who are pregnant or breastfeeding should refrain from consuming swordfish to ensure the well-being of both mother and child. For those who enjoy this fish, savoring it in moderation can be delightful, with grilling, stewing, or boiling being popular cooking methods that enhance its robust flavor.