On February 27, 2022, the National Cancer Center of China released its latest China Cancer Report, "Cancer Incidence and Mortality Rate in China in 2016". The data shows that in 2016, there were about 4.06 million new cancer cases in China. As a disease with a high fatality rate, it is reasonable for people to "talk about cancer discoloration", and it is better to treat diseases than to prevent diseases, how to stay away from cancer, which has become a topic of concern more and more.
People take food as the sky, "food carcinogenic theory" is endless, those cancer-related "food carcinogenic theory" which is true and which is false?
1. Will I get cancer when I eat pickles?
In order to keep green vegetables for a longer time, our ancestors invented pickled vegetables through accumulation of experience and exploration. However, with the World Health Organization's International Agency for Research on Cancer (IARC) in 1993 listing traditional Asian pickles as a Class 2B carcinogen, eating pickles equated with getting cancer.
The list of carcinogens of the World Health Organization's International Agency for Cancer can be found on the official website of the State Drug Administration of China. Item 323 on the list is Pickled vegetables traditional Asian traditional Asian sauerkraut.
The list shows that in addition to traditional Asian pickles, people like malaria, red meat, progesterone, and even car exhaust are all class 2B carcinogens.
Moderator Liang Yin
What are Class 2B carcinogens? Why is this pickle that Chinese often eaten put in class 2B carcinogens?
Analyst Zhang Kai
The World Health Organization's Cancer Research Institute (IARC) classifies carcinogens into the following four categories:
A. Grade 1 carcinogen, which has been shown to have carcinogenic effects on the human body.
2. 2 A class carcinogens and 2B carcinogens, 2A class carcinogens have been confirmed to have carcinogenic effects on animals, but there is not enough evidence of carcinogenic effects on humans, 2B evidence of carcinogenicity in humans is limited, and evidence of carcinogenicity in animals is insufficient; or insufficient evidence of carcinogenicity in humans, sufficient evidence of carcinogenicity in animals.
Grade 3 carcinogens are not sufficiently evidenced to be carcinogenic to animals and humans, or are carcinogenic to animals but not carcinogenic to humans.
Class IV.4 carcinogens refer to substances that have not yet been proven to be carcinogenic and are likely not carcinogenic to humans.
The main route of cancer induced by pickles is nitrite.
We know that in order to determine carcinogenicity, in addition to the nature of the substance, we also need to consider the dose and time. So we measured the amount of nitrite in the pickles, "speaking" with data.
The Press Assurance Team starts with the following aspects:
First, in different types of pickles, what is the value of nitrite it contains, and is there any difference?
Second, will the nitrite content in pickled vegetables change with the time of pickling?
To this end, we contacted the Hangzhou "Dad Evaluation" team that has done the above experiments and has received widespread attention in the field of science popularization.
Experimental process and discovery:
The experiment selected fresh Shanghai green and cabbage and pickled for 35 days.
The results show that:
The nitrite content of pickled greens peaked on day 7: 420 mg/kg, then began to decline, still 155 mg/kg on day 14, 29 mg/kg on day 28, and 6.5 mg/kg on day 35.
The nitrite content of pickled cabbage peaked at 29 mg/kg on day 7 and dropped to 2.9 mg/kg on day 14.
GB 2762-2017 "National Standard for Food Safety Limits of Contaminants in Food" states that the nitrite content of pickled vegetables should be controlled below 20mg/kg.
Through comparison, we can see that for homemade pickled vegetables, in the 5th week, its nitrite content will drop below the national standard. For pickled cabbage, it already meets the national standard in week 2.
Statistics show that there is no statistical relationship between the proportion of stomach cancer in China and the intake of nitrite-rich foods, but there is this causal relationship in Westerners.
While the second reason why pickled vegetables cause it to be a class 2B carcinogen may be salt, a high-salt diet and esophageal cancer and stomach cancer are absolutely closely related.
Therefore, the news that "eating pickles will cause cancer" is false.
2. Will cooking in an air fryer cause cancer?
The epidemic has changed a lot of our way of life, and in the days when we were locked up at home, many people became masters of cooking, and the use of the "everything can be fried" air fryer soared. However, the saying that cooking in an air fryer causes cancer has also come along, and will this be true?
"Foods containing carbohydrates produce acrylamide when cooked at more than 120°C, and the longer the heating time, the higher the heating temperature, the more acrylamide is produced." This is the number one reason on the Internet that food cooked in an air fryer is considered to cause cancer.
The first item in the List of Carcinogens of the World Health Organization's International Agency for Cancer (IARC) was Acrylamide, a subclass of AA, which was added to the list in 1994.
When it comes to fried foods, many people's first reaction is French fries. Therefore, this time the French fries as the primary experimental testing ingredient, "Dad Review" carried out the above experiments and obtained relevant data.
Experimental process and discovery
Experiments are conducted with the same ingredients and ratios and at different times or temperatures.
The fries of the air fryer vs the fryer are fried, and the values of the acrylamide are as follows:
Number one is an air fryer: acrylamide content up to 4100 mcg per kilogram
Number two is an air fryer: acrylamide content of 810 mcg per kilogram
Number three is an air fryer: acrylamide content of 39 mcg per kilogram
Fryer: The value of acrylamide is 260 mcg per kilogram
According to the experimental data of the "Dad Review", we can see that whether it is fried or using an air fryer, acrylamide is produced when frying Fries. And as netizens said, the longer the cooking time, the drier and more scorched the frying, the more acrylamide is produced.
The european union sets a benchmark level of less than 500 micrograms per kilogram for residual acrylamide in French fries, and if you buy a good quality air fryer, control the time and temperature to operate, it can be lower than this standard value.
Therefore, the news that "cooking in an air fryer can cause cancer" is false.
3. "Overnight water is carcinogenic" and "overnight vegetables are carcinogenic"?
Regarding the "overnight water carcinogenic" and "overnight vegetables causing cancer", there have been such sayings, in the overnight water and overnight dishes, are there any carcinogens?
The debate over the health effects of overnight tea has focused on three main areas:
First, the content of nitrate and nitrite in overnight tea has increased significantly, and there is a risk of carcinogenicity;
Second, the bacteria in the overnight tea will increase, and drinking will make the stomach trouble;
Third, the tea polyphenols of overnight tea will be lost and lose their nutritional value.
The search continued on the World Health Organization's International Agency for Cancer (IARC) list of carcinogens, finding in item 53 "nitrate or nitrite ingested under conditions that cause endogenous nitrosation", a Class 2A carcinogen that was listed in 2010.
Moderator Liang Yin
What is the relationship between nitrates and carcinogenesis?
Analyst Zhang Kai
Nitrates themselves are not carcinogens. Nitrate is one of the most common nitrogen-containing inorganic substances in nature, but in some cases, nitrate will be processed and reduced by some bacteria, including the human body, and it will become nitrite after the reduction reaction.
Experimental process and discovery
In order to make the experiment more convincing, the "Dad Review" selected three kinds of tea that people usually drink, namely black tea, green tea and oolong tea, and set the standard of "overnight" 24 hours after brewing.
According to the brewing requirements of different tea leaves, black tea, green tea and oolong tea are brewed at 90 °C, 80 °C, and 100 °C for 3 minutes, 4 minutes and 2 minutes respectively.
The result is:
Nitrate content:
Oolong tea: from 15mg/kg to 12mg/kg,
Green tea: from 10 mg/kg to 12 mg/kg
Black tea: Keep at 9 mg/kg
Nitrite content:
Oolong tea: from 0.7 mg/kg to 0.9 mg/kg
Green tea: from 0.6 mg/kg to 1.3 mg/kg
Black tea: from 1.5 mmg/kg to 1.2mg/kg
It can be seen that the content of nitrate and nitrite in overnight tea is traceable, and the health impact on the human body is negligible.
We noticed that the tea polyphenols contained in tea leaves are effective against tumors. The less tea is processed, the higher the polyphenol content of the tea. So, the tea polyphenols of overnight tea will be lost and lose their nutritional value, is it true?
Experimental process and discovery
We also conducted experiments on the changes in tea polyphenols in overnight tea and found:
The polyphenol content of freshly brewed green tea tea is 2742mg/kg.
The polyphenol content of green tea tested overnight is 2778mg/kg.
The results showed that the tea polyphenols in overnight tea were not lost.
Below, we continue to experiment with colony changes in overnight tea.
Experimental process and discovery
After just brewing and 24 hours after brewing, samples are taken in sterile bags twice, and then sent to the local laboratory in time for a total flora test.
Whether it is green tea, black tea or oolong tea, the total number of fungi detected overnight is less than 10 CFU/ml.
Continue to view GB 5749-2006 drinking water sanitation standards, which states: For drinking water, the total number of colonies should be controlled at 100 bacteria / ml, it can be concluded that the total number of colonies in the three kinds of tea after overnight is less than one-tenth of the national standard requirements.
Therefore, the long-term health risks or increased health benefits caused by the flora in overnight tea are actually completely negligible.
After verifying the overnight tea, will the overnight dish have a carcinogenic risk?
There are two main points of discussion about the health effects of overnight dishes:
First, the nitrite in overnight dishes exceeds the standard, which may cause carcinogenesis;
Second, the colony content in overnight dishes exceeds the standard, which may affect the health of the body.
Experimental process and discovery
In order to make the experiment more scientific, the "Dad Evaluation" team selected a total of 32 kinds of raw materials commonly found in the market for testing.
The leftover dishes are grouped into two groups: the ambient group (25 degrees Celsius) and the refrigerated group (4 degrees Celsius).
One sample was taken after just finishing meal and 6 hours, and after 12 hours and 24 hours, respectively.
The results show:
Refrigeration group: No nitrite content was detected.
Room temperature group: after 12 hours there is a significant rise,
More than 20 mg/kg.
After 24 hours, the nitrite content of the vegetables has significantly exceeded 100mg/kg.
What about colonies in overnight dishes? We also conducted experiments.
Experimental process and results
In the case of cold cucumbers, for example, the total number of initial colonies is relatively high, reaching 7.1×10 cfu/g.
At 6 hours under refrigeration conditions, 8.3×10 cfu/g have been reached.
At 25 degrees Celsius, the total number of communities of cold cucumbers after 6 hours is 1.9×10 cfu/g, which is already a relatively high value.
Some cooked meats are relatively low, taking braised meat as an example:
Under refrigeration conditions, the total number of braised meat bacteria was still less than 100 cfu/g until 12 hours, and 1.7×103 cfu/g after 24 hours.
Braised pork at room temperature reached 300 cfu/g at 12 hours and 2.3 × 104 cfu/g at 24 hours.
Therefore, the safety of overnight dishes has a lot to do with their storage conditions and timing. From the perspective of nutrition, the nutritional value of vegetables will decline sharply with the extension of the shelf life. Therefore, overnight dishes really do not have much nutritional value for everyone.
In this issue, we have verified a set of very widely circulated claims related to food cancer, hoping to help you.
Staying away from cancer and embracing health is our common goal.
Editor of this issue: Zhang Heng
Guest: Zhang Kai (Deputy Director, Department of Cancer Prevention, National Cancer Center of China, Cancer Hospital, Chinese Academy of Medical Sciences)
Investigator: Haoran Ma
Text Editor: Wu Yanan Yu Erya
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