雅思阅读 187: Fermented Foods and the Gut Microbial Frontier（发酵食品与肠道微生物前沿）

改编自 Nutrients / Frontiers in Microbiology。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://pmc.ncbi.nlm.nih.gov/articles/PMC6723656/

Reading Passage

A. Fermentation is one of the oldest forms of food processing on Earth. Long before refrigeration, humans discovered that leaving milk, cabbage, soybeans or meat in the right conditions let microbes transform it into something more stable, digestible and often more interesting to the taste. Yoghurt, kefir, sauerkraut, miso, natto, kimchi and dosa are all products of this ancient technology, developed independently across every inhabited continent. For most of the twentieth century, fermentation was studied mainly as a food-preservation technique. In the last two decades, however, it has become one of the most intensively investigated topics in nutritional science, because the microbes that ferment food do not simply vanish when the food is swallowed — they interact with, and potentially reshape, the trillions of microorganisms that inhabit the human gut. Sales of probiotic products now run into billions of dollars annually, but the science behind the marketing is still young. Most consumers who buy a yoghurt drink for "gut health" do so on the basis of advertising claims that outpace the clinical evidence.

B. The gut microbiome — the community of bacteria, fungi and viruses living in the intestine — has been linked in recent research to everything from immune function and mood to metabolic disease and even response to certain cancer treatments. If what we eat can alter that community, then food becomes a kind of medicine. Fermented foods are attractive candidates because they deliver large quantities of live, beneficial bacteria — principally lactic acid bacteria such as Lactobacillus and Bifidobacterium — directly into the digestive tract. These organisms produce organic acids, including lactic, acetic and propionic acid, which lower the pH of the intestine and selectively suppress pathogenic bacteria while favouring the growth of species already associated with good health. They also generate short-chain fatty acids (SCFAs), metabolites that feed the cells lining the colon and reduce systemic inflammation. The hypothesis is appealing in its simplicity: eat bacteria, change the gut, change health. Whether it actually works in practice is a different question.

C. Randomised trials have begun to test whether these laboratory findings translate into real benefits. A prominent trial at Stanford University compared a high-fermented-food diet against a high-fibre diet over several weeks. The fermented-food group, consuming items such as yoghurt, kefir, kombucha and fermented vegetables, showed a clear increase in overall gut microbial diversity — a result that nutritional scientists consider broadly beneficial, because a more diverse microbiome is generally more resilient. The changes were durable, persisting after the trial ended. By contrast, the high-fibre group did not show the same increase in diversity over the same period, a result that surprised researchers who had expected fibre to be the more powerful modulator. Other trials have focused on specific products. A randomised study of kefir in healthy young adults found that it increased the relative abundance of Bifidobacterium and species of Blautia, a genus associated with SCFA production. The Stanford trial also measured inflammatory markers in the blood, which fell in the fermented-food group but not in the fibre group.

D. Yet the picture is far from simple. A crossover trial examining sauerkraut — both fresh and pasteurised — in healthy participants found no overall change in the composition of the gut microbiota, even though individual bacterial species did shift and serum levels of SCFAs rose. The authors concluded that the specific composition of the sauerkraut itself, the strains used and the degree of processing mattered a great deal, and that a single fermented food should not be treated as interchangeable with another. Not all fermented foods contain live cultures: pasteurisation after fermentation kills the organisms, and many commercial products labelled "probiotic" contain strains chosen for shelf stability rather than for their ability to survive stomach acid and colonise the intestine. A systematic review of foodborne microbes from traditional and probiotic fermented foods concluded that the interaction between food and gut microbiota is real but complex, and that whether a given strain actually takes up residence in the gut — as opposed to simply passing through — depends on the starting microbiome of the individual eater. Two people eating the same yoghurt may therefore have very different responses. The starting gut community, the rest of the diet, and even the time of year can shape how a fermented food is received. This is why identical trials can produce seemingly contradictory results in different populations. The microbiome is not a single organ; it is an ecosystem.

E. The result is a cautious consensus. Fermented foods are almost certainly healthier than the ultra-processed products they often replace, and regular consumption of a variety of traditionally fermented foods appears to be a reasonable dietary choice. But the idea that a single yoghurt drink or capsule can reliably "repair" a damaged microbiome is not supported by the evidence. The microbes in food must compete with an established ecosystem, and their effects are moderated by everything else the person eats. The most promising direction is not a universal probiotic pill but a personalised approach — matching fermented foods to the composition of the individual gut, using different products at different times. That vision is still years from routine clinical practice, but it explains why fermented foods, after thousands of years on the dinner table, have become one of the most active research frontiers in human nutrition. The next decade will determine whether the gut microbiome turns out to be as malleable — and as therapeutic — as its most enthusiastic proponents believe, or whether the relationship between a spoonful of yoghurt and a person's long-term health turns out to be far more modest than the advertising suggests. Either way, the fermentation that humans practised for millennia before vitamins were discovered is finally being studied with the seriousness it deserves.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. Why fermented foods matter for the gut microbiome ii. The history of refrigeration iii. What randomised trials have shown iv. Why the evidence is more complicated than it looks v. A cautious consensus and future directions vi. How to manufacture yoghurt in a factory vii. Why antibiotics are better than probiotics

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. What do lactic acid bacteria in fermented foods do in the intestine? A. They raise the pH and encourage pathogens. B. They produce organic acids that lower pH and suppress harmful bacteria. C. They are destroyed entirely by stomach acid. D. They replace all other gut bacteria.

6. What did the Stanford high-fermented-food trial find? A. Fermented foods decreased gut microbial diversity. B. High-fibre foods were always superior. C. The fermented-food group showed increased gut microbial diversity. D. No changes were observed in either group.

7. What did the sauerkraut crossover trial conclude? A. Sauerkraut completely rewrote the gut microbiome. B. There was no overall change in gut microbiota composition, though serum SCFAs rose. C. Pasteurised sauerkraut was more effective than fresh. D. Sauerkraut caused digestive problems in all participants.

8. Why is the idea of a universal probiotic pill not supported? A. Probiotic pills are too expensive to produce. B. Food microbes must compete with an established gut ecosystem, and effects vary by individual. C. All probiotic pills have been proven dangerous. D. The gut cannot accept any new bacteria.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. Fermentation was developed in Europe and spread to other continents.
10. A more diverse gut microbiome is generally considered more resilient.
11. The high-fibre group in the Stanford trial showed the largest increase in diversity.
12. Pasteurisation after fermentation kills the live organisms in the food.
13. Probiotic pills have been shown to cure diabetes in clinical trials.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

Fermented foods deliver live bacteria that produce (14) __________ acids, which lower intestinal pH and generate (15) __________ that feed the cells lining the colon.

答案与解析

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