Swordfish (Xiphias gladius) is a large predatory fish that many people around the world consume.
Its characteristic feature is a sword-like bill, which is where its name comes from. It’s also one of the fastest known fish in the ocean.
Swordfish has a distinctive nutritional profile and provides many health-promoting effects. However, consuming it too frequently or in large amounts may lead to mercury toxicity (1Trusted Source).
This article reviews the health effects of eating swordfish, including its benefits and downsides, and how much is safe to eat.
Swordfish nutrition
Swordfish is rich in multiple essential nutrients.
Essential nutrients are ones your body cannot produce, so you need to get them from food.
A 3-ounce (85-gram) serving of cooked swordfish provides (2Trusted Source):
- Calories: 146
- Protein: 20 grams
- Fat: 6.7 grams
- Carbs: 0 grams
- Selenium: 106% of the Daily Value (DV)
- Vitamin D: 71% of the DV
- Potassium: 9% of the DV
- Magnesium: 7% of the DV
Swordfish is exceptionally high in selenium. This essential trace mineral is important for human health due to its role in thyroid and bone metabolism, immunity, heart health, and male fertility, among other functions (3Trusted Source, 4Trusted Source).
It’s also a great source of vitamin D, a key vitamin for bone health that has also proven beneficial for immunity, heart health, and asthma (5Trusted Source, 6Trusted Source).
Additionally, swordfish is a fatty fish with high amounts of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
EPA and DHA are also essential and known to protect against heart and inflammatory diseases and help improve brain health (7Trusted Source, 8Trusted Source).
A 3-ounce (85-gram) serving provides 764 mg of EPA and DHA combined. The 2015–2020 Dietary Guidelines for Americans recommend consuming an average of 250 mg per day. Thus, swordfish is a very rich source (2Trusted Source, 9Trusted Source).
SUMMARY
Swordfish is rich in essential nutrients necessary for health, including selenium and omega-3 fatty acids.
Benefits of eating swordfish
Swordfish may provide multiple health benefits, mostly due to its high omega-3, selenium, and vitamin D contents.
May lower risk factors for heart disease
High blood pressure and cholesterol levels are both risk factors for heart disease.
Omega-3 fatty acids found in swordfish may positively influence blood pressure and cholesterol levels, especially in people with a preexisting heart condition. They don’t appear to interfere with prescription drugs (10Trusted Source, 11Trusted Source, 12Trusted Source).
Research shows that EPA and DHA may lower your blood pressure by decreasing your heart rate and improving blood vessel function and elasticity (11Trusted Source, 13Trusted Source).
They may also lower your blood triglycerides by approximately 20–30% and help prevent blood clots from forming and clogging your arteries (11Trusted Source).
However, they may increase LDL (bad) cholesterol levels, a risk factor for heart disease (11Trusted Source).
Additionally, the vitamin D in swordfish may lower your blood pressure and risk of heart attack. In fact, one study found that people with vitamin D deficiency had a 60% higher risk of heart disease (14Trusted Source, 15Trusted Source, 16Trusted Source, 17Trusted Source, 18Trusted Source).
Evidence suggests that taking vitamin D supplements may lower systolic blood pressure (the top number of a blood pressure reading) by 2–6 mm Hg. It may do this by interacting with multiple systems in your body, including your kidneys and endocrine system (19Trusted Source).
May reduce the risk of cancer
Swordfish may help protect against cancer thanks to its omega-3, vitamin D, and selenium contents.
Inflammation is a predisposing factor for cancer, and omega-3s and vitamin D have anti-inflammatory properties. Studies suggest that both nutrients may help protect against colorectal cancer (14Trusted Source, 20Trusted Source).
Both nutrients may prevent cancerous cells from reproducing and induce their death. Additionally, vitamin D may help stop the growth of new blood vessels that feed those cells (14Trusted Source, 20Trusted Source).
Omega-3s also help prevent cancer from spreading, a process called metastasis. Animal and human research also show that they may reduce colorectal tumor size. However, studies in humans show inconsistent results (20Trusted Source, 21Trusted Source, 22Trusted Source).
As for selenium, it acts as a powerful antioxidant that fights the cancerous effects of excess free radicals in the body. It may have a protective effect against liver, prostate, breast, and lung cancers (23Trusted Source, 24Trusted Source, 25Trusted Source).
Taking selenium supplements may also help people undergoing radiotherapy improve their quality of life and reduce the therapy’s side effects (26Trusted Source).
While this research shows promising results, it’s important to note that it evaluates the effects of particular nutrients, not the effects of eating swordfish itself. Thus, scientists need to do more research on the effects of swordfish specifically.
May boost bone health
The vitamin D and selenium in swordfish may improve bone health.
Vitamin D’s primary role in your body is to stimulate calcium absorption in the gut. It also plays an essential role in bone formation, and its deficiency is linked to bone loss and increased risk of falls and fractures (14Trusted Source, 27Trusted Source, 28Trusted Source, 29Trusted Source).
While selenium is less well known than vitamin D, it also plays a role in promoting bone health by influencing bone metabolism. This process is mediated by bone cells called osteoblasts and osteoclasts.
In a process called bone remodeling, osteoblasts synthesize bone tissue, and osteoclasts break it down to release minerals into your bloodstream. Selenium helps maintain a balance by inactivating osteoclasts to prevent brittle bones (30Trusted Source).
Studies have found that low selenium blood levels were associated with an increased risk of low bone mineral density and bone disease (30Trusted Source).
SUMMARY
The omega-3 fatty acids, vitamin D, and selenium found in swordfish may improve heart and bone health and help reduce the risk of certain cancers.
Downsides
Including swordfish in your diet may provide multiple benefits. However, this fish also comes with an important drawback — it has a high mercury content.
Mercury is a reactive heavy metal that comes mostly from waste and coal burning. The mercury waste from these processes ends up in lakes and oceans from rainwater (31Trusted Source).
Small aquatic organisms absorb it, and then larger predators absorb it by eating them. In this way, the mercury moves up the food chain from prey to predator. Larger, longer-living predators, such as swordfish, tend to contain higher quantities (31Trusted Source, 32Trusted Source).
As a neurotoxin, mercury has a toxic effect on the brain. People with a high intake of predatory fish — over five servings per week — are particularly at risk. Mercury intake may even diminish the beneficial effects that omega-3s have on heart health (33Trusted Source, 34Trusted Source).
It’s especially dangerous for babies’ central nervous system development. Research shows that mercury can cross the placenta or be passed to babies via breast milk (1Trusted Source, 31Trusted Source, 35Trusted Source).
Thus, pregnant and breastfeeding people should avoid eating swordfish (36Trusted Source).
SUMMARY
Swordfish contain high amounts of mercury, a heavy metal with toxic effects on the brain, and it’s especially dangerous for babies’ brains.
How to cook it
Swordfish is a meaty fish with a slightly sweet flavor and firm texture. You can prepare it with or without marinade. People often make oil-based marinades for it containing fresh herbs.
It’s usually cut into 1-inch (2.5-cm) fillets and grilled or cooked in the same way as a rare beef steak. Though people often discard the skin due to its rubbery texture, you may want to keep it on during cooking and then discard it afterward to help make the fish juicier.
Other common cooking methods include boiling and stewing. The firm texture of swordfish prevents it from flaking or breaking apart.
While people don’t usually deep-fry swordfish, this is another possible preparation method.
However, it’s a rather unhealthy one, as deep-fried foods lead to the formation of trans fatty acids (TFA), which may increase risk factors for heart disease (37Trusted Source, 38Trusted Source).
When buying swordfish, make sure the fillets don’t show any discoloration, darkening, or drying around the edges. They should also smell fresh, not fishy or rancid (39Trusted Source).
You can safely refrigerate raw swordfish for 2 days before cooking it, or you can store it frozen for up to 3 months. Once cooked, it may keep for up to 4 days in the fridge or 6 months in the freezer (40Trusted Source).
SUMMARY
Swordfish is a meaty fish that people usually cook and serve in a similar style to beef steak. Aside from grilling it, you can also boil, stew, or fry it.
The bottom line
Swordfish is a popular fish rich in omega-3 fatty acids, selenium, and vitamin D, which confer numerous health benefits.
Research has found these nutrients are associated with improved heart and bone health and a lower risk of cancer.
However, it’s high in mercury, a toxic trace metal with detrimental effects on brain health, especially on babies’ developing brains. For this reason, pregnant and breastfeeding people should avoid eating swordfish.
You may enjoy an occasional serving of swordfish by grilling, stewing, or boiling it.
