One reason is enough to advise you to eat more yam!

Yam is a treasure food in autumn. It can be eaten as a meal or used for cooking. Think of yam fried with three delicacies, blueberry yam, candied yam, steamed yam, millet yam porridge, yam and pork ribs soup...all of them are delicious. I really advise you to eat more yam, there are still many benefits~

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How nutritious is yam? The starch content of yam is not low. According to the data in the Chinese Food Composition Table, the carbohydrate content of yam is 12.4g/100g. [1] Literature shows that the starch content in different varieties of yam tubers varies greatly, with a total range of 11.6% to 29.2%, and an average starch content of 18.7%. [2] The carbohydrate content of potatoes and sweet potatoes, which are often eaten as staple foods, is 17.8% and 15.3% respectively. In this way, yam can be considered a high-starch food.

1 iron stick of yam. Image source: The author The potassium content of yam is also quite good, at 213 mg/100 g. [1] Although not as high as potatoes, it is higher than sweet potatoes, nearly 2.5 times that of sweet potatoes. In addition, yam also contains yam polysaccharides, cholesterol, ergosterol, brassicasterol, β-sitosterol, polyphenol oxidase, phytic acid and saponins. [3]

The benefits of eating yam regularly are that the Chinese Dietary Guidelines recommend that Chinese people eat 50-100 grams of potato foods every day, and yam is one of them. Now that yam is in season, I suggest you take the opportunity to eat more, because it has so many benefits for the body.

3 cm diameter, index finger length yam, 2 pieces weigh about 100 grams. Image source: author

Six yams that are as thick as a finger and as long as a middle finger weigh about 100 grams. Image source: author

1. Control your weight and lose weight

Yam is a high-starch potato food, which is very suitable for replacing part of refined rice and white flour as a staple food. Its calorie is only 57kcal/100g, which is equivalent to the calorie of apples, lower than sweet potatoes and potatoes, and only 1/6 of that of polished rice. Therefore, replacing part of white rice with yam will be very helpful for weight control and weight loss.

2. Protect myocardium and control blood pressure

Eating 100 grams of yam can provide 213 mg of potassium, which can meet 11% of the daily potassium requirement of the general population. Excessive potassium intake in the diet can help us maintain normal myocardial function, maintain cell osmotic pressure and acid-base balance, and help control blood pressure. This may be related to the fact that potassium can directly promote urinary sodium excretion, inhibit the renin-angiotensin system and the sympathetic nervous system, improve the function of pressure receptors, and directly affect peripheral vascular resistance. [4]

3. Anti-inflammatory

Inflammatory factors can cause damage to our bodies. Anti-inflammatory treatment can improve inflammatory factors in the body, reduce their damage to the body, and prevent them from developing into diseases. The yam polysaccharides, glycoproteins, and diosgenin in yam can achieve anti-inflammatory effects by inhibiting bacteria, resisting oxidation, reducing the expression of inflammatory factors, and activating and regulating inflammation-related pathways. [5]

4. Control blood lipids and blood sugar

Studies have shown that yam polysaccharides can regulate blood lipid metabolism disorders by reducing malondialdehyde levels, increasing reduced glutathione levels, and high-density lipoprotein cholesterol levels. They also have the effect of lowering blood sugar levels. The yam with the highest polysaccharide content is found in the Huai River yam from Hebei Province. [5]

In addition, yam is a low-GI food, with a GI value of only 51. [1] Using it to replace some staple foods such as white rice and white steamed bread can help control blood sugar after meals. Some studies have also mentioned that the allantoin contained in yam can improve the function and quality of pancreatic beta cells, reduce beta cell apoptosis, and thus lower blood sugar. [6]

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5. Antioxidant

The polyphenol compounds in yam mainly include flavonoids, phenolic acids, tannins and anthocyanins, which can help us remove excess free radicals in the body and play an antioxidant role. Currently, there are few studies on yam polyphenol compounds, which are mainly focused on iron stick yam, Huai yam and Huai yam. The content of these compounds is ranked from high to low as follows: iron stick yam > Huai yam > Huai yam > purple yam. [5]

Why do my hands always itch when handling yam?

Although eating yam has many benefits, when it comes to processing yam, everyone is very troubled. The most common feeling is "too! itchy!!"

If you peel yam with your bare hands, most people will feel itchy. This is because there is a lot of mucus when the yam is peeled, which is mainly a complex polysaccharide composed of polysaccharides and proteins. Studies have shown that yam mucin can prevent cardiovascular fat deposition and is one of the components of yam that protects arteries.

Yam mucus. Image source: author

Some people believe that the reason why hands itch when handling yam is because it contains saponins, but there is currently no research literature that clearly points out that the saponins in yam are the "real culprit" that causes allergies.

However, there are studies that have specifically investigated allantoin in yam mucus. The researchers divided mice into two groups and shaved the hair on their necks and backs. They injected allantoin into the necks of the mice in the experimental group and injected saline into the necks of the mice in the control group. They then observed and collected the number of times the mice in the two groups scratched within an hour. The results showed that the number of times the mice in the experimental group scratched their necks was significantly higher than that in the control group. [7] This suggests that allantoin can cause an allergic reaction in the necks of mice. Therefore, the "real culprit" of yam mucus causing itchy hands may be allantoin, and it is not ruled out that saponins may also have some influence. Another study also mentioned that the yam itch pattern is a rapid onset of itching accompanied by a burning sensation. This itching occurs within tens of seconds to minutes after the skin first comes into contact with fresh yam juice, and there is no wheal during the itching. This itching pattern is very similar to the itching pattern caused by cysteine ​​proteases.

It is speculated that the mechanism by which yam causes itching may be that the proteases in yam activate PAR and cause non-histamine-dependent itching. [8]

5 tips to relieve itching when dealing with yam

The allantoin in yam is afraid of heat and will decompose when exposed to heat. It is also afraid of alkaline liquids. Cysteine ​​protease is also a heat-sensitive component and can be inactivated by high temperatures. So when handling yam, you can refer to the following 5 suggestions to avoid itchy hands to the greatest extent!

1. Wear gloves when handling yams

Wear disposable gloves before peeling the yam. The gloves have a protective function and can prevent the skin from directly contacting the yam mucus. Be careful not to cut your hands.

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2 Use chopsticks to poke

Use a chopstick to penetrate the yam and place the other end against a wall that is easy to clean. Don't grab the yam directly with your hands, just grab the chopsticks. This way you won't touch the skin when peeling the yam.

3 Steam first, then peel

You can steam it first and then peel it. In this way, the allergenic substances in the yam will be decomposed by heat during the steaming process, and it will not itch when you handle it. If you find it troublesome, just eat it with the skin.

4. Wash your hands and bake

If you touch the yam mucus, wash your hands immediately, then roast it over the fire, or blow it with the hot air setting of a hair dryer, but be careful not to get burned by the nozzle of the hair dryer.

Summarize:

Yams are really worth eating in autumn. When buying them, you can ask what kind they are and then decide how to eat them. No matter what kind of yam you eat, you have to eat less rice, otherwise you may gain weight.

References

[1] Yang Yuexin. Chinese Food Composition Table 6th Edition Volume 1[M]. Peking University Medical Press, 2018

[2] Shu Rui, Li Xiaolong, Nie Yujie, et al. Comparative analysis of the main nutritional components of different varieties of yam [J]. Seed Science and Technology, 2019, 37(13): 33-34.

[3] Sun Changhao. Nutrition and Food Hygiene. 8th edition. People's Medical Publishing House. 2018

[4] Yang Yuexin, Ge Keyou. Chinese Nutrition Science Encyclopedia 2nd Edition (Volume 2)[M]. People's Medical Publishing House, 2019

[5] Liu Xinyue, Wang Fengzhong, Fan Bei, et al. Research progress on the health benefits of different varieties of yam [J/OL]. Chinese Food and Nutrition: 1-7 [2023-10-07].

[6] GO Hyeon Kyu, RAHMAN Md Mahbubur, KIM GBeum, et al. Antidiabetic Effects of Yam (Dioscoreabatatas) and Its Active Constituent, Allantoin, in a RatModel of Streptozotocin-Induced Diabetes [J]. Nutrients2015, 7(10): 8532-8544.

[7] Yang Yan, Zhu Jing, Li Defeng, et al. Study on itch-causing substances and itch-causing mechanisms in yam[J]. Progress in Biochemistry and Biophysics, 2019, 046(010): 1012-1019.

[8] Sun Donghong, Hong Yuxiao, Chen Hongduo, et al. Analysis of yam protein and its itch-causing components[J]. Journal of China Medical University, 2021, 50(12): 1069-1075.

Author: Xue Qingxin Member of Chinese Nutrition Society Registered Nutritionist Health Manager Public Nutritionist

Review | Ruan Guangfeng, Deputy Director of Kexin Food and Health Information Exchange Center