Lychees have such a high sugar content, why do people still suffer from low blood sugar after eating them?

Produced by: Science Popularization China

Author: Denovo Team

Producer: China Science Expo

“If I could eat 300 lychees a day, I would be willing to live in Lingnan forever.” Throughout the ages, lychees have captured the hearts of the people with their soft and glutinous texture, rich juice, and sweet taste, making countless eaters fall for them.

However, while enjoying the wonderful taste of lychees, are you aware of the "sweet trap" hidden behind them?

Figure 1: Lychee

(Image source: pixabay)

Where is the “hometown” of litchi?

Before talking about the etiquette and precautions of eating lychees, let’s first talk about the origin of lychees.

Litchi is mainly produced in the subtropical areas of southern China, among which "Fei Zi Xiao" is one of the most popular high-quality varieties. Recently, a study in the journal Nature Genetics successfully completed the genome assembly of "Fei Zi Xiao" with the help of genomic sequencing data, deciphering the life code of litchi for us. By analyzing the resequencing data of 72 litchi resources, the researchers proposed the hypothesis of "one origin center and two independent domestication events" for litchi .

This discovery shows that the origin of litchi is actually Yunnan Province in China, and after continuous propagation, it formed a wild population in Hainan . Since then, litchi in Yunnan and Hainan have been domesticated independently into early-maturing and late-maturing varieties, respectively. The common "Fei Zi Xiao" is a hybrid of the early-maturing variety in Yunnan and the late-maturing variety in Hainan. Research on the litchi genome will help us to further explore its functional genes and cultivate better varieties.

Figure 2: a. Schematic diagram of litchi fruit; b. Litchi genome map; c. Litchi genome characteristics; d. Phylogenetic analysis of litchi genome; e. Comparison of synonymous mutation rates among different litchi varieties

(Image source: Reference [1])

Can eating lychees induce hypoglycemia?

Delicious lychees are certainly hard to resist, but eating too much can easily have adverse effects on your health and may even cause people to suffer from "lychee disease" - an acute neurological disease caused by lychees that mainly occurs in children. Its clinical symptoms are similar to those of hypoglycemia, including dizziness, fatigue, pale complexion, palpitations, abdominal pain and diarrhea, and hunger.

Wait, hypoglycemia? Some people may wonder, lychees are so sweet and have such a high sugar content, how can eating too much of them cause hypoglycemia?

This starts with the different types of sugar.

Sugars can be divided into oligosaccharides, monosaccharides and polysaccharides according to their degree of hydrolysis. Among them, common monosaccharides are glucose and fructose . Fructose is the most abundant in lychee, and what we usually call hypoglycemia actually refers to low glucose levels in the body.

Figure 3: Blood glucose measurement

(Photo source: veer photo gallery)

Studies have shown that litchi is rich in deglycin A and methylenecyclopropylglycine , and the content of these two substances is higher in unripe litchi. These two substances inhibit the normal oxidation of fat and gluconeogenesis (the process of converting non-sugar precursors into glucose) in the body, thereby interfering with glucose synthesis.

Therefore, when we eat a lot of lychees, the glucose level in the body can no longer meet the normal metabolic needs of the human body, the sugar balance is disrupted, and hypoglycemia symptoms appear. In addition, the energy supply of brain tissue mainly comes from glucose. Hypoglycemia caused by excessive consumption of lychees will also reduce the energy supply to the brain, which will have a certain impact on brain metabolism and may even cause brain damage. This situation is particularly serious in children. Therefore, you must eat lychees in moderation and do not overeat.

Figure 4: Eating lychees

(Image source: pixabay)

Caught driving under the influence after eating lychees?

Whenever lychees are on the market, there are always news reports about people being mistakenly convicted of drunk driving after eating lychees. Why is this?

It turns out that lychees contain a lot of sugar, and during storage, lychees undergo anaerobic respiration, breaking down sugars into carbon dioxide and alcohol . Therefore, when people eat a lot of lychees, alcohol tests may show a positive reaction. However, this is a false drunk driving , which is fundamentally different from real drunk driving. After all, lychees can produce less alcohol and stay in the body for a relatively short time. With breathing and talking, the alcohol can evaporate and will no longer be detected.

Therefore, if you are caught driving under the influence after eating some lychees, you can first explain the situation to the traffic police, wait for a while and then go for retest. However, it is best not to eat too many lychees before driving!

Figure 5: Alcohol tester

(Photo source: veer photo gallery)

What are the precautions when eating lychees?

(1) Moderation is key

The Chinese Dietary Guidelines recommend that adults should consume 200-400 grams of fruit per day. Considering the diversity of food, it is best for adults to eat no more than 10 lychees a day, and for children no more than 5.

(2) Avoid eating on an empty stomach

When the stomach is empty, the human digestive system is in a fragile state. Eating litchi at this time can easily induce nausea, acid reflux and other problems. Therefore, it is best to eat litchi half an hour after a meal.

(3) Be cautious when eating unripe lychees

Unripe lychees have higher levels of norglycine A and methylenecyclopropylglycine, which can easily increase the risk of "lychee disease". Therefore, when buying lychees, you should choose ripe lychees. In addition, it is worth noting that once lychees are picked, their maturity will not change. Unlike fruits such as bananas and mangoes, which can be "ripened", you must see clearly whether the lychees are ripe or not when choosing.

However, in addition to the above three points, everyone should also grasp the appropriate amount of lychee intake according to their own physical condition! I don’t know if you have understood these details about lychees. Let us not forget to be responsible for our health and eat them reasonably while enjoying the delicious lychees!

References:

[1] Hu, G., et al., (2022) Two divergent haplotypes from a highly heterozygous lychee genome suggest independent domestication events for early and late-maturing cultivars. Nature Genetics. doi.org/10.1038/s41588-021-00971-3.

[2] Aakash Shrivastava, PhD, Anil Kumar, MD, et al. Association of acute toxic encephalopathy with litchi consumption in an outbreak in Muzaffarpur, India, 2014: a case-control study. 30, 2017. DOI: https://doi.org/10.1016/S2214-109X(17)30035-9.

[3] Liu Ying. Clinical analysis of 71 cases of litchi disease in children[J]. Guangxi Medicine, 2000, 22(5):2.