What should we pay attention to when supplementing calcium? Why should we blanch spinach and water spinach before eating?

Author: Qu Tiebing, Chief Physician, Beijing Boai Hospital, China Rehabilitation Research Center, Deputy Director of the Joint Surgery Group, Orthopedics Branch, Chinese Medical Association

Reviewer: Zhao Yu, Chief Physician, Peking Union Medical College Hospital

If you are calcium deficient, you can get some calcium from food. Under the guidance of a doctor, you can also take appropriate calcium preparations and drugs that promote calcium absorption, such as vitamin D, which can effectively improve the calcium deficiency and prevent the occurrence of osteoporosis.

People often say that we should eat more foods rich in calcium. But which foods are high in calcium? This is a question that modern people are particularly concerned about.

1. Which foods in daily life are high in calcium?

Seafood contains relatively high amounts of calcium, such as dried shrimp, fish, kelp, and seaweed.

Many seafood products also contain phosphorus, which can promote calcium absorption. Calcium supplementation without phosphorus is not easy to absorb. This is also one of the reasons why it is easy to supplement calcium by eating seafood.

Calcium and magnesium are also related. There is a saying that goes, "If you take calcium supplements without magnesium, you will regret it." Magnesium is a trace metal element. Its content is slightly higher in meat products, and it is also contained in seafood.

Among vegetables, spinach, leeks, and water spinach contain relatively high amounts of calcium; among bean products, tofu skin, also known as dried tofu, contains the highest amount of calcium, with 1,100 mg of calcium per kilogram. Tofu is made of gypsum and is in a semi-solidified state. The thinner the tofu, the lower the calcium content, because the main ingredient is water. For example, Japanese tofu does not contain much calcium. In addition, milk contains calcium, and loach also contains a high amount of calcium.

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Are meat foods high in calcium?

There is a saying that "big fish and meat eat up calcium". After big fish and meat are broken down into amino acids, they combine with calcium ions in the gastrointestinal tract and are then excreted. Calcium absorption will be reduced. This mainly refers to fat meat. Lean meat contains calcium and can be eaten, but it is not good to consume too much.

Don't expect to complete calcium supplementation after eating these calcium-containing foods. It's not the case. It just means that eating these high-calcium foods can supplement the daily calcium needs, but it is different from calcium supplementation. Patients with severe calcium deficiency need additional calcium preparations under the guidance of a doctor.

When getting calcium from food, you should also pay attention to the processing method. For example, spinach and water spinach should be blanched before eating.

2. Why do we need to blanch spinach and water spinach before eating?

The calcium contained in spinach and water spinach is mainly calcium oxalate. After calcium oxalate is dissolved in water, it is particularly easy to decompose oxalic acid. After oxalate ions enter the body, they will combine with calcium ions in the serum. Then they will be deposited in the kidneys, precipitating crystals to become stones, which can easily lead to kidney stones.

Therefore, when eating spinach and water spinach, it is best to blanch them in water first. After blanching for a few minutes, a lot of oxalic acid will be filtered out, but the calcium will remain in the vegetables.

The body can supplement its daily calcium needs through food, but some foods, which we call junk food, may affect calcium absorption after eating, such as carbonated drinks, fried foods, high-salt foods, etc.

3. Why does drinking carbonated drinks and eating fried foods affect calcium absorption?

Calcium is in a synthetic state in nature, such as calcium sulfate, calcium carbonate, etc. What we eat is synthetic calcium, and what we absorb is ionic calcium. After calcium ions enter the bones, they become synthetic calcium again. In other words, calcium exists in the bones in the form of calcium carbonate.

Carbonated drinks and fried foods can easily turn calcium ions decomposed in the body into calcium carbonate, which combines prematurely in the gastrointestinal tract, preventing the calcium from entering the serum, let alone the bones.

High-fat foods and carbonated beverages are not healthy foods. It doesn't mean that you must not eat or drink them. If you drink carbonated beverages and eat high-fat foods every day, you will probably be calcium deficient.

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4. Will eating too much salt also lead to calcium deficiency?

Strictly speaking, no one has discussed this aspect in medicine, but sodium ions and calcium ions are both classified as electrolytes in medicine. These ions are in a state of dynamic equilibrium in the body. If you have more, I will have less, and if I have more, I will take up your space. This situation may happen.

But what is certain is that high salt is not good for people. In a high salt state, the osmotic pressure in the serum will be high. High osmotic pressure will absorb a lot of water from the serum, causing edema and swelling, causing physiological metabolic disorders, requiring a lot of water, increasing the burden on the heart, and leading to many diseases. From this perspective, a high-salt diet is not recommended.