True butterfish (the small, silvery Atlantic species) is a nutritious, low-mercury fish that delivers solid protein and healthy fats. A 100-gram serving contains 146 calories, 17 grams of protein, and 8 grams of fat with zero carbohydrates. But there’s a catch worth knowing about: a completely different fish called escolar is frequently sold under the name “butterfish,” and eating it can cause unpleasant digestive side effects. Whether butterfish is healthy depends entirely on which fish you’re actually getting.
Nutritional Profile of True Butterfish
The Atlantic butterfish (Peprilus triacanthus) is a small, flat fish found along the eastern coast of North America. According to NOAA Fisheries, a 100-gram raw serving provides 17 grams of protein and 8 grams of fat, including 3.4 grams of saturated fat. It has 65 milligrams of cholesterol and 89 milligrams of sodium.
Beyond the macros, butterfish is a good source of selenium and vitamin B12. A single cooked fillet provides about 21% of your daily selenium needs and 19% of your daily B12. Selenium supports thyroid function and acts as an antioxidant, while B12 is essential for nerve health and red blood cell production. You also get a modest 6% of your daily phosphorus from one fillet.
Like most seafood, butterfish is a zero-carb, high-protein food that fits comfortably into heart-healthy and low-carb eating patterns. Its fat content is moderate compared to very lean white fish like cod, but that fat carries omega-3 fatty acids that benefit cardiovascular health.
Mercury Levels Are Very Low
One of butterfish’s strongest selling points is its low mercury content. FDA testing found a mean mercury concentration of just 0.058 parts per million across 89 samples. For context, the FDA considers fish with mercury levels below 0.1 ppm to be among the lowest-mercury options available. That puts butterfish in the same safety tier as salmon, sardines, and shrimp.
This makes it a safe choice for pregnant women, nursing mothers, and young children, all of whom are advised to eat two to three servings of low-mercury fish per week. You would have to eat extremely large quantities of butterfish for mercury to become a concern.
The Escolar Problem
Here’s where things get complicated. A large, deep-water fish called escolar is routinely mislabeled and sold as “butterfish” in restaurants and fish markets. These are completely different species. Escolar can weigh over 100 pounds. True butterfish rarely exceeds one pound. But because escolar has a rich, buttery texture, the nickname has stuck, and the mislabeling is widespread.
The FDA’s official acceptable market names for escolar are “escolar” or “oilfish.” Calling it “butterfish” or “white tuna” on a label constitutes seafood fraud. Yet it happens frequently enough that if you’ve eaten “butterfish” at a sushi restaurant or from a counter where the fillets were large and thick, there’s a reasonable chance it was actually escolar.
Why Escolar Causes Digestive Issues
Escolar contains up to 20% of its body weight in waxy compounds called gempylotoxins. These are a type of wax ester that the human digestive system simply cannot break down. They pass through your intestinal tract undigested, which can cause a condition called keriorrhea: oily, orange or yellow liquid stool that can appear without warning. The experience is uncomfortable and sometimes alarming, though it isn’t dangerous in a medical sense. Symptoms typically show up within a few hours of eating and can last a day or two.
Because of this effect, several countries have restricted or banned the sale of escolar entirely. Japan, Italy, and South Korea have all imposed restrictions at various points. In Australia, regulations require that escolar be sold with advisory labels, and health authorities there recommend specific precautions for anyone who does eat it.
How to Tell What You’re Getting
If you’re buying a whole, small fish (roughly the size of your hand, thin and silvery), you’re likely looking at true Atlantic butterfish. If the fillet is large, white, and thick, with a very rich, oily texture, it’s almost certainly escolar.
At restaurants, ask directly whether the fish is escolar or true butterfish. Reputable establishments will know the difference and label it correctly. At grocery stores, check the species name on the packaging if available. True butterfish will list Peprilus triacanthus or simply “butterfish.” Escolar should be labeled Lepidocybium flavobrunneum.
Reducing Risk If You Eat Escolar
If you enjoy escolar and want to keep eating it, portion size is the most important variable. Australian health authorities recommend limiting any single serving to less than 200 grams (about 7 ounces). Many people who experience keriorrhea have eaten large portions, sometimes 300 grams or more in a sitting.
Cooking method also matters. Grilling escolar allows much of the wax-ester-rich fat to drain away during cooking, which reduces (but doesn’t eliminate) the risk. You should discard any liquid that drains off during cooking rather than using it in sauces or side dishes. Some sources suggest that removing the skin and the layer of flesh just beneath it, a technique called deep skinning, might help. However, the Queensland Government notes that it remains uncertain whether deep skinning reliably removes enough wax ester oil to prevent symptoms.
The Bottom Line on True Butterfish
Genuine butterfish is a healthy, protein-rich fish with very low mercury, meaningful amounts of selenium and B12, and the kind of fat profile that nutritionists encourage. It’s a smart seafood choice by almost any measure. The only real risk comes from accidentally eating escolar that’s been mislabeled as butterfish, which won’t harm you long-term but can cause a memorably unpleasant few hours. Knowing the difference between these two fish is the single most useful thing you can do to make sure your “butterfish” dinner is both healthy and enjoyable.