Is eating vegetables raw the healthiest? There are many ways to lock in VC

In the pursuit of fresh and nutritious diets, vegetable salads and cold dishes have replaced meat and fish, becoming the main focus of the "meal show party" in the circle of friends. Many people believe that cooking will cause the loss of nutrients in vegetables, especially vitamin C, which everyone is more concerned about. Eating vegetables raw can not only retain more nutrients, but also taste the original flavor of the food.

Although this perception is somewhat reasonable, we cannot generalize all vegetables. Different vegetables have different nutrients and properties, so they are suitable for different cooking methods. Which vegetables are suitable for eating raw and which vegetables should never be eaten raw? How can we cook them to retain more vitamin C? Let's find out!

01 Do not eat these vegetables raw as they may reduce your absorption and may even be life-threatening

Vegetables are an important way for us to take in dietary fiber, minerals, vitamins and antioxidants. Raw vegetables have not been processed in any way, and the nutrients are intact, which means we can eat more nutrients. But not all vegetables can be eaten raw. For example, the following two types are harmful to health when eaten raw:

① Vegetables with high oxalic acid content: Oxalic acid is considered an anti-nutritional factor. It reacts with mineral ions such as calcium and magnesium to form insoluble precipitates, affecting the absorption of minerals. Long-term intake of oxalic acid will also increase the risk of urinary stones and kidney stones.

One study found that the absorption rate of magnesium in a diet containing spinach, which is high in oxalic acid, was only 26.7%, while in a diet containing cabbage, the absorption rate of magnesium reached 36.5%. This difference is mainly attributed to the difference in oxalic acid content in the two vegetables. [1]

Proper cooking can remove some of the oxalic acid in vegetables, such as the commonly used blanching method. In an experiment, spinach and amaranth were heated in clean water. The higher the water temperature, the lower the oxalic acid retention rate. The experimenters placed these two vegetables in 90 ºC hot water. The oxalic acid retention rate in amaranth was 80.1% (1 minute) and 42.6% (3 minutes), while the oxalic acid retention rate in spinach was 77.5% (1 minute) and 37.5% (3 minutes). As the soaking time was extended from 1 minute to 3 minutes, the oxalic acid content of both vegetables decreased by nearly 40%. [2]

Therefore, vegetables with high oxalic acid content such as spinach, amaranth, celery, and water spinach are not suitable for eating raw. If they are blanched and eaten, the absorption of nutrients will be better than eating them raw.

② Vegetables that contain toxins: For example, beans and green beans contain saponins and lectins, which can cause nausea and vomiting if eaten raw, and can even be fatal in severe cases. The thermal stability of these two toxic substances is relatively poor, and heating can destroy their toxicity, making them safer to eat.

02 These vegetables can be eaten raw without worrying about their original flavor and are healthy

Most vegetables can be eaten raw, such as tomatoes, cucumbers, onions, bell peppers, lettuce, zucchini, purple cabbage, white radish, carrots, etc. The only concern is that some people worry about pesticide residues and the use of plant growth regulators.

In fact, this worry is a bit unnecessary. Pesticides and plant growth regulators exist to ensure that we have enough food to eat. Without them, perhaps the vegetables we eat are all worm-eaten or diseased, or the yield is so low that it is not enough to eat. In addition, my country's "Law on the Quality and Safety of Agricultural Products" also clearly stipulates that wholesale markets for agricultural products should establish or entrust agricultural product quality and safety testing institutions to conduct random inspections on the quality and safety of agricultural products sold on the market. Only products with pesticide residues that do not exceed the standard are qualified products. Plant growth regulators are classified as pesticides in my country, and each plant growth regulator also has a clear scope of use and residual dosage requirements.

Even if there are a few violations, as long as we choose to buy vegetables from regular channels, we can reduce this risk. Now some large supermarkets have even opened self-service product traceability query equipment. Where the product was produced and what its qualifications are, just scan the code to clearly know, to ensure that consumers buy and eat with peace of mind.

03 Choosing the right cooking method makes it so easy to lock in vitamin C!

Since not all vegetables can be eaten raw, how to cook vegetables that cannot be eaten raw to retain more vitamin C is another issue that people are concerned about. Here are some tips to help vegetables "lock in vitamin C".

A. Don’t forget to add some salt and vinegar when blanching.

We mentioned above that blanching vegetables is an effective way to remove oxalic acid, but reducing the oxalic acid content will also reduce the vitamin C content. This is related to the fact that vitamin C is afraid of heat and is highly soluble in water. Generally, the loss rate of vitamin C in vegetables is 70-90% after boiling for 5-10 minutes. If the original juice is squeezed out and then soaked for more than an hour, the vitamin C loss rate may be as high as 90% or more. [3]

But don't worry, as long as you use the following two tricks during the blanching process, you can retain more vitamin C~

① Add some vinegar: The retention rate of vitamin C in vegetables during cooking will decrease as the pH increases, and it is more stable under acidic conditions. Therefore, you can add some vinegar during the blanching process to lower the pH value during cooking, so as to obtain more vitamin C. This method is also applicable to cooking!

② Add some salt: As the salt concentration increases, the retention rate of vitamin C will also increase to a certain extent. An experiment has made observations on spinach and amaranth in this regard. When these two vegetables were blanched in 1% salt concentration, the vitamin C retention rates of spinach and amaranth were 68.5% and 65.7% respectively; when the salt concentration was increased to 5%, the vitamin C retention rates of spinach and amaranth were 77.6% and 73.6% respectively.

However, we must remind everyone that if salt is added when blanching vegetables, remember to reduce the amount of salt used in the subsequent cooking process, or simply not use salt or other salt-containing seasonings to avoid salt intake exceeding the daily standard of 6 grams.

B. Stir-fry quickly over high heat

When cooking, it is best to use a quick stir-fry method, which heats up quickly and takes a short cooking time, which can reduce the time vegetables are heated, retain more nutrients, and reduce the loss of vitamin C. In general, when cooking, you should: wash first and then cut, stir-fry quickly, add vegetables to soup, and eat immediately after stir-frying.

C. Mostly steam or microwave

For most vegetables, steaming and microwaving are the best cooking methods for retaining vitamin C. The cooking temperature of both methods is lower than that of stir-frying. Using a small amount of water and controlling the cooking time during the cooking process will be more beneficial to the retention rate of vitamin C. [4]

▲Figure: Reference: "Chinese Nutrition Science Encyclopedia"

D. Cooking with a non-stick pan:

There is another secret that many people don’t know, that is, using a non-stick pan to cook can retain more vitamin C.

An experiment observed the effects of cooking with four types of pots: aluminum pots, iron pots, copper pots, and non-stick pots on vitamin C. The results showed that cooking with aluminum pots caused the least loss of vitamin C, about 0% to 12%; while the loss of vitamin C with iron pots could reach 0% to 30.7%; and the loss of vitamin C with copper pots could be as high as 30% to 70%. This is because metal ions accelerate the oxidation of vitamin C. [5, 6] Generally, non-stick pots are made of aluminum and stainless steel, and have a coating on them to prevent vegetables from coming into direct contact with metal. Therefore, in comparison, it is more recommended to use non-stick pots to cook vegetables.

At this point, some readers may worry that "the coating of non-stick pans is toxic and cooking with it may cause cancer." The coating of non-stick pans is made of Teflon. Studies have shown that Teflon is safe below 250°C. Other studies have shown that when the temperature exceeds 202°C, it will release toxic and harmful substances, especially when the coating is scratched. [7]

But no matter which of the above statements is true, there is no need to worry too much. The temperature of our normal cooking does not usually exceed 200 degrees. As long as you pay attention to avoid scratching the coating by cooking hard food when using a non-stick pan, and try to add a small amount of cooking wine or water to control the temperature when cooking, the non-stick pan can be used with confidence.

Although eating vegetables raw can help us take in more nutrients, not all vegetables are suitable for eating raw. Vegetables with high oxalic acid or those that contain toxins are not recommended for eating raw. Vegetables that need to be cooked can follow the above suggestions to minimize the loss of nutrients.

References:

[1] Zhang Yingpeng, Yang Yunjuan, Yang Li, Li Yan, Gao Bimo, Wang Xuejun, Dong Xiaoxia. Oxalic acid damage in plants and its control measures[J]. Anhui Agricultural Science Bulletin, 2007(10):34-39+92.

[2] Zhao Gongling, Liang Xinhong, Kong Jin. Effects of blanching on oxalic acid and vitamin C in spinach and amaranth[J]. Food Industry Science and Technology, 2010, 31(01): 367-368+401.

[3] Yang Yuexin, Ge Keyou. Chinese Nutrition Science Encyclopedia 2nd Edition (Volume 1)[M]. People's Medical Publishing House, 2019.698.693

[4] Wang Fengli, Fang Rui, Qin Liming, Yao Jiaqian, Liu Ruonan, Liu Dongmei, Zhou Peng. Research progress on the effects of cooking methods on vegetable nutrition, antioxidant capacity and color [J/OL]. Food Industry Science and Technology: 1-15 [2021-06-19]

[5] Zhao Hongjing, Yang Yuexin. Vitamin loss during food processing and cooking. Foreign Medical Hygiene, 2003, 4 (30): 221-226. [6] Geng Xinghai. Vitamin loss during vegetable processing and cooking. Jiangsu Food and Fermentation, 2009, 1: 28-29.

[7] Lü Xiancheng, Sun Hang, Cao Lei, Qin Haofeng, Wan Yong, Gao Jianguo. Effect of operating temperature on tribological properties of Teflon non-stick coating for food contact[J]. Surface Technology, 2020, 49(03): 155-161.

Author | Xue Qingxin, member of Chinese Nutrition Society, registered dietitian, registered nutrition technician, health manager, public nutritionist

Review | Song Shuang, Associate Researcher, Institute of Nutrition and Health, Chinese Center for Disease Control and Prevention

This article was first published on Science Refutes Rumors