Can You Safely Cook Onions with Fish and Shellfish? Debunking Myths

Is it true that onions contain oxalic acid and should not be consumed with fish, shrimp, or crab?

Hello, I often use onion ice cubes to cook food, and recently I saw online that onions should not be eaten with certain types of food, including fish, shrimp, and crab.
"Fish is rich in protein, and when eaten with onions, the oxalic acid in onions can break down.
When eaten with shrimp, it can easily form calcium oxalate, leading to stone formation." However, isn't onion considered a low-oxalate food? Can onions be cooked with fish?

Niming, 30~39 year old female. Ask Date: 2017/03/20

Dr. Cai Xiuwen reply Nutrition

Hello~ Regarding the causes of kidney stones, there are many factors that influence their formation.
For generally healthy individuals, consuming certain foods does not directly lead to the development of stones.
However, for those with a predisposition to stones, dietary choices may warrant more attention as they could influence stone formation.

Although many stone components contain calcium, it is not accurate to say that calcium-rich foods are the sole cause of stones.
Several factors can affect the formation of stones, including: 1.
Inadequate fluid intake or low urine output.
2.
Excessive salt intake.
3.
High protein consumption.
4.
Excessive vitamin C intake, which can lead to increased oxalate levels in urine.
5.
Individual body constitution.

Therefore, onions are considered low-oxalate foods, and cooking them with fish will not contribute to stone formation.
There is no need for excessive concern; maintaining a balanced diet and drinking plenty of water is sufficient.
This information is provided by Dietitian Tsai Hsiu-Wen from Nantou Hospital, Ministry of Health and Welfare.
Wishing you peace and good health.

Reply Date: 2017/03/20

More Info

Cooking onions with fish and shellfish is a common practice in many culinary traditions, and there are several myths surrounding the safety and health implications of this combination. Let's delve into the details to clarify these concerns.

Nutritional Composition of Onions and Fish
Onions are indeed low in oxalates, which are compounds that can contribute to the formation of calcium oxalate stones in susceptible individuals. The idea that onions contain high levels of oxalates and can lead to stone formation when cooked with fish or shellfish is largely unfounded. In fact, onions are primarily composed of water, carbohydrates, and a variety of vitamins and minerals, including vitamin C, B vitamins, and potassium. They also contain antioxidants, such as quercetin, which may have health benefits.

Fish and shellfish, on the other hand, are excellent sources of high-quality protein, omega-3 fatty acids, and essential nutrients like vitamin D and selenium. Combining these two food groups can create a nutritious meal that is rich in flavor and health benefits.

Myths About Cooking Onions with Fish and Shellfish
1. Oxalate Concerns: The claim that onions can form calcium oxalate stones when cooked with fish or shellfish is misleading. As mentioned, onions are low in oxalates, and the amounts present are not significant enough to pose a risk of stone formation when consumed in reasonable quantities.

2. Digestive Issues: Some people believe that combining onions with fish or shellfish can lead to digestive problems. While certain individuals may experience discomfort from specific food combinations, this is not a universal reaction. It is essential to consider personal tolerance levels rather than generalizing about food pairings.

3. Flavor Compatibility: From a culinary perspective, onions can enhance the flavor of fish and shellfish dishes. They add sweetness and depth, making them a popular ingredient in various recipes, such as seafood stews, fish tacos, and grilled fish preparations.

Safety Considerations
When cooking fish and shellfish, it is crucial to ensure that all ingredients are fresh and properly handled to avoid foodborne illnesses. Here are some safety tips:
- Freshness: Always use fresh fish and shellfish. Check for signs of spoilage, such as an off smell or slimy texture.

- Cooking Temperature: Cook fish and shellfish to the appropriate internal temperature to kill harmful bacteria and parasites. Fish should reach an internal temperature of 145°F (63°C), while shellfish should be cooked until they are opaque and firm.

- Cross-Contamination: Use separate cutting boards and utensils for raw fish and shellfish to prevent cross-contamination with other foods, including onions.

Conclusion
In summary, cooking onions with fish and shellfish is safe and can be beneficial from a nutritional standpoint. The myths surrounding oxalate formation and digestive issues are largely unfounded. As with any food combination, individual tolerance may vary, so it is essential to listen to your body and adjust your diet accordingly. If you enjoy the flavor of onions in your seafood dishes, feel free to include them without concern for adverse health effects. Always prioritize food safety practices to ensure a healthy and enjoyable cooking experience.

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