Recently, a paper was published in the top academic journal Cell. Researchers fed mice with soluble dietary fibers (SDF), and the mice unexpectedly developed liver cancer. [1]
Related papers (image source: Cell)
Dietary fiber is believed to be understood by everyone, many foods contain dietary fiber, for example, celery, leeks, oats. So can't we eat all these foods?
The answer, of course, goes to the paper.
First, there is the purpose of the study. The paper opens by mentioning that as living standards rise, people are consuming more and more sugar and fat, and accordingly, obesity rates have risen and metabolic diseases have increased. Previous studies have shown that dietary fiber can lead to weight loss. In this case, adding dietary fiber to foods seems like a good idea. The question is, how effective.
That said, explain. The so-called dietary fibers (dietary fibers, DF) are those sugars in plants that cannot be used by the body. According to the source, it can be divided into three kinds, natural, extracted from plants and synthetic. According to physical properties, they can be divided into two categories.
The first type is not soluble in water, called insoluble dietary fiber (IDF), although it can not be digested and absorbed by the body, but can be a small collection of water, increase the feeling of satiety, stimulate intestinal peristalsis, promote defecation. The second category is the main protagonist of the study, water-soluble dietary fibers (SDF), which are a little more hydrophilic and can be partially utilized by intestinal bacteria, by bacterial fermentation, decomposition, and assisting in the absorption of other nutrients. [2,3]
The next step was the experimental subjects. The researchers wanted to know if water-soluble dietary fiber could improve metabolic diseases while reducing weight. So they chose T5KO rats without the TLR5 gene. Because it lacks this gene, it can develop gut flora disorders and metabolic diseases.
That said, explain a bit more.
When a baby is first born, the gut is sterile. As they eat, bacteria begin to colonize the gut. Then the grind begins bacteria stimulate the immune system and promote immune system development, and in turn, the immune system picks off bacteria, so everyone's gut flora is not quite the same.
To use an analogy, bacteria are like vendors, the gut is the street, and the immune cells are the city police. Without hawkers, it is inconvenient to buy things, and too many hawkers and disobedience to management will also cause inconvenience to the people. The management process requires the participation of enthusiastic citizens, and for the human body, the enthusiastic citizen is the TLR5 gene, which is responsible for recognizing the flora in the intestine and determining whether to make a report call (activating the MYD88 pathway). [4]
The next step is the experiment.
The first step of the experiment was to feed the mice with an inulin-rich diet (7.5 percent of the total diet), and as a result, the mice did lose weight, but serologic tests showed abnormal bilirubin, which is usually indicative of abnormal liver function. So the researchers continued to feed the mice and were dismayed to find that, after six months, 40 percent of the mice developed liver cancer.
Here, inulin is mentioned. Inulin is a soluble substance extracted from chicory root, i.e., from the source, inulin belongs to the second category, artificially extracted and enriched, and from the physical properties, inulin belongs to the water-soluble dietary fiber.
The researchers then did two types of experiments. One type was to study other rats, and the results showed that some rats of other species lines, again, would develop liver cancer, but not rats lacking MYD88. This suggests that dysbiosis of gut flora is inextricably linked to liver cancer.
Finally, the researchers tried controlling the rats' gut flora, for example, by knocking it out with antibiotics, and the rats turned out to be fine no matter how much inulin they were fed.
So, what should we, the average person, think about this study?
First of all, some scholars have measured the dietary fiber in daily food, and the results show that the naturally occurring dietary fiber, mainly insoluble (IDF), soluble (SDF) relatively speaking, much less. [5]
Dietary Fiber Content and Categories in Common Foods [5]
Secondly, this study is in conflict, with previous studies. Inulin has a long history of use, and there is little in the past literature that questions its safety. [6]
Even if you eat it, the average person doesn't eat that much. It is estimated that the average European consumes 3 to 11 grams of inulin per day. [6]
Referring to the Dietary Guidelines for Chinese Residents, adding oil, salt, and meat together, all in accordance with the maximum appropriate amount of counting, the most you can eat in a day is 1821 grams of food. Want to use the results of human replication experiments, dietary fiber accounted for 7.5%, that is 137g research shows that the daily intake of dietary fiber more than 80g, it will cause bloating. It's an impossible task.
Inulin intake in Europe and North America[6]
Dietary Pagoda (Image source: Dietary Guidelines for Chinese Residents, 2016)
What's more, the fact that rats without the TLR5 gene developed liver cancer, and rats deficient in MYD88 didn't, amply demonstrates that the key lies in the fact that inulin is fermented and broken down by the products of inulin, which affects the intestinal flora, and the immune system plays a played an important role, so the conclusions of the experiment can not be replicated in normal people.
Finally, you can't just look at the drawbacks, but also the benefits. Numerous studies have confirmed the health benefits of dietary fiber, weight loss, improved metabolism, lower cancer rates, and more. [7]
For example, a 20-year follow-up showed that consuming enough dietary fiber in early adulthood can significantly reduce the incidence of breast cancer. [8]
The Chinese Academy of Nutrition recommends a daily intake of 25 to 30 grams of dietary fiber, and successive surveys have shown that residents in both urban and rural areas fall short of the standard intake. [2]
Dietary fiber intake survey [2]
In fact, in the interview, the authors of the paper then mentioned that the inulin used in the experiment is not a natural food, but is chemically raised and processed; their purpose, too, is not simply to blame the water-soluble fiber, but rather, they hope that people will realize that extra dietary fiber added to the food may not necessarily have the fruits and vegetables are good. [9]
All in all, the significance of this experiment is that If you stay on a high-fat, high-sugar diet, and expect to maintain your weight with extra added dietary fiber, you may not get what you pay for.
The correct approach should be to refer to reliable books such as the Dietary Guidelines for Chinese Residents, analyze your own dietary patterns, and eat more celery, leeks, and oats if your dietary fiber intake is insufficient, and completely change your lifestyle habits.
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References
[1]SINGH V, YEOH B S, CHASSAING B et al. Dysregulated Microbial Fermentation of Soluble Fiber Induces Cholestatic Liver Cancer[J]. Cell, 2018, 175(3): 679-694.e22.
[2]Chinese Nutrition Society. Dietary nutrient reference intake for Chinese residents (2013 edition)[M]. Science Press, 2014.
[3]B.O S. Soluble vs insoluble fiber: different physiological responses.[J]. Food technology, 1987.
[4]Chunfeng Wang. Interaction between intestinal ****ogenic microorganisms and immune system[J]. Journal of Jilin Agricultural University, 2018, 40(4): 475479.
[5]Yin Wenya, Huang Chengyu, Feng Liang. Determination of dietary fiber in different kinds of food[J]. Health Research, 2004, 33(3): 331333.
[6]COUSSEMENT P A A. Inulin and Oligofructose: Safe Intakes and Legal Status[J]. The Journal of Nutrition, 1999, 129(7): 1412S-1417S.
[7]MCRORIE J W. Evidence-Based Approach to Fiber Supplements and Clinically Meaningful Health Benefits, Part 1[J]. Nutrition Today, 2015, 50(2): 8289.
[8]FARVID M S, ELIASSEN A H, CHO E et al. Dietary Fiber Intake in Young Adults and Breast Cancer Risk[J]. Pediatrics, 2016, 137(3): e20151226.
[9]Adding refined fiber to processed food could have negative health effects, study finds[EB/OL]. ScienceDaily, [2018-10-22]. . The op-ed articles published on this website represent the views of the authors and are not related to this website. In case of infringement, the article is responsible for its own.
Author: Zhao Yanchang