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Fiber and your gut bacteria: coverage of small, preliminary study raises many questions, offers few answers


3 Star


In Defense of Fiber: How Changing Your Diet Changes Your Gut Bacteria

Our Review Summary

fiberThe story focuses on a June paper from the journal BMJ, which looked at the role that a particular bacterium found in the human gut (Akkermansia muciniphila) may play in influencing metabolic health and reports that a high-fiber diet can influence an individual’s population of A. muciniphila. The story does a good job of explaining what happened in the study and providing outside expert commentary on the role of fiber in regulating the immune system. It also communicates what we think is a good science-based message about the value of a diet rich in a variety of plant foods. But the story doesn’t explain for readers the many limitations of the study or the fact that there was significant variability in how a fiber-rich diet affected an individual’s A. muciniphila levels. And the number of qualifiers needed in discussing the study raise the question of why this study was written about at all. Why not wait for the additional research that’s needed? There is a lot of speculation here about how this bacterium might impact obesity, with a paucity of evidence to back it up.


Why This Matters

Research that can help the public make informed decisions on how to maintain a healthy body weight and control related risk factors, such as blood sugar level and cholesterol, has real value. However, there can also be value in not covering a single study — particularly when that study is promising, but really only points the way to more targeted research that may have more relevant findings. In this instance, at least one of the researchers is already working on a follow-up study that focuses specifically on the impact that A. muciniphila may have on reducing risk factors for cardiovascular disease. Looking at the BMJ study in conjunction with the findings of that ongoing study (and of other work in the field on fiber and the gut microbiome) may offer greater insight into the role of A. muciniphila (and fiber) in helping to maintain cardiovascular health.


Does the story adequately discuss the costs of the intervention?

Not Applicable

The story does not mention cost. However, the intervention being discussed here is increasing one’s dietary fiber intake. And the cost of high-fiber foods is widely variable. While some high-fiber foods may be costly (e.g., fresh vegetables are not readily available for those in urban “food deserts”), others — such as beans — are not. We’ll rate this Not Applicable.

Does the story adequately quantify the benefits of the treatment/test/product/procedure?

Not Satisfactory

The story states that: “People who started out with lower stores of Akkermansia had more after they followed the fiber-rich calorie-restricted diet. You can increase these bacterial populations by eating fiber, Cani’s research suggests, which acts as a prebiotic in the gut and has a beneficial effect on some bacteria.” We applaud the cautious language used here (i.e., employing the phrase “research suggests”). However, that language only presents half of the research findings. As the BMJ paper itself reports, study participants who began the study with higher levels of A. muciniphila actually saw their abundance of the bacteria decline after following the six-week, high-fiber, calorie-restricted dietary intervention in the study. And that decrease in A. muciniphila abundance continued even after the participants returned to a more “normal” diet for an additional six weeks. While it’s not clear if that decrease in A. muciniphila has any affect on reducing health risks, it’s worth mentioning. In addition, the story would have been more useful for readers if it had offered even general information on what constitutes a “healthy” amount of fiber. For example, Harvard’s School of Public Health reports that adults and children should get “at least 20 to 30 grams of fiber per day.”

Does the story adequately explain/quantify the harms of the intervention?

Not Applicable

The story does not discuss risks associated with increasing your intake of dietary fiber. However, that’s likely because there are few (if any) health risks associated with increasing fiber in your diet. We’ll rate this Not Applicable.

Does the story seem to grasp the quality of the evidence?

Not Satisfactory

The story says the study evaluated 49 overweight and obese adults over the course of “a six-week calorie-restricted diet (between 1,500-1,800 calories per day) while increasing their fiber intake. The diet was followed by six weeks of eating normally. They kept a food journal throughout, and the researchers biopsied their fat tissue.” That’s a fine description of what happened, but the story doesn’t place the study design in any sort of context for readers. For example, there was no control group — is that relevant for this type of study? And is this study capable of telling us whether higher A. muciniphilaIs levels caused the beneficial changes in health risk factors that were observed or whether they were merely associated with those outcomes? (Maybe bacteria levels are simply a reflection of some other characteristic of certain people that causes them to respond better to calorie restriction?) Is 49 study participants a large enough sample size to be meaningful? Some comment on these limitations would have strengthened the coverage substantially.

Does the story commit disease-mongering?


The story does a good job of distinguishing between risk factors and actual health problems. No disease mongering here.

Does the story use independent sources and identify conflicts of interest?


The story includes one source who was not affiliated with the relevant study, but makes clear that the source is a vocal proponent of the idea that a high-fiber diet is important for maintaining a “healthy” gut microbiome and that the microbiome can have a significant impact on health.

Does the story compare the new approach with existing alternatives?

Not Satisfactory

The story was mostly about gut bacteria, but it does discuss the potential impact of A. muciniphila on cholesterol, glycemia (i.e., blood sugar levels), and other risk factors for cardiovascular disease. It would have been useful here to discuss other interventions, such as exercise, that can influence these risk factors.

Does the story establish the availability of the treatment/test/product/procedure?


The story mentions a range of healthy dietary options for increasing fiber intake — all of which are available to consumers.

Does the story establish the true novelty of the approach?


The story makes clear that the recent BMJ study is part of a larger field of work evaluating both the role of gut bacteria in human health and the role of dietary fiber in influencing the make-up of the gut microbiome. (It even links to another study on fiber and the American diet.) However, the story would have been stronger if it had included slightly more information, or links to additional information, that would have helped readers place the new work in context.

Does the story appear to rely solely or largely on a news release?


The story incorporates input from an independent source, references outside research, and does not appear to draw from a news release.

Total Score: 5 of 8 Satisfactory


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