{"id":8239,"date":"2026-07-22T17:37:17","date_gmt":"2026-07-22T15:37:17","guid":{"rendered":"https:\/\/bacteria.de\/uncategorized\/fiber-deficiency-microbiome\/"},"modified":"2026-07-22T17:50:31","modified_gmt":"2026-07-22T15:50:31","slug":"fiber-deficiency-microbiome","status":"publish","type":"post","link":"https:\/\/bacteria.de\/en\/nutrition\/fiber-deficiency-microbiome\/","title":{"rendered":"No Protection Without Fiber?"},"content":{"rendered":"\n

How a Lack of Fiber Harms the Gut<\/h1>\n\n
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Dietary fiber\u2014or at least some types of it\u2014feeds the bacteria in the human gut. This strengthens the bacteria that are important for human health. But what happens when dietary fiber is lacking? When the bacteria in the gut run out of food? Then some of them look for a new food source\u2014and eat the gut\u2019s protective mucus layer. <\/p>\n<\/blockquote>\n\n

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The German Nutrition Society<\/a><\/strong> recommends at least 30 grams of dietary fiber<\/strong> per day. This recommendation was supported in 2019 by a large meta-analysis that synthesized the results of many studies. The analysis showed that a daily dietary fiber intake of more than 25 grams was associated with a lower risk of mortality<\/strong>. In addition, these individuals were less likely to develop coronary heart disease<\/strong>, stroke<\/strong>, type 2 diabetes<\/strong>, and colorectal cancer<\/strong>. Fiber therefore appears to play an important role in human health. <\/p>\n\n

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Why is dietary fiber so important?<\/h2>\n\n

The human body can utilize dietary fiber<\/a> only to a very limited extent, if at all. As a result, it reaches the large intestine largely undigested<\/strong>, where the majority of bacteria live. Not all dietary fiber is processed the same way there: Some is fermented by bacteria and thus serves as food for them, while <\/strong>other types can be broken down only to a very limited extent, if at all <\/strong>. Non-fermentable dietary fiber primarily supports bowel motility<\/strong> and influences the speed<\/strong> at which food passes through the intestines. Fermentable dietary fiber<\/strong> is particularly important for the microbiome. <\/p>\n\n

The bacteria in the gut have special enzymes\u2014a sort of toolbox<\/strong>\u2014that allow them to break down carbohydrates, including dietary fiber, and use them as food. The human body has just 17 enzymes<\/strong> for this purpose, whereas the microbiome has a huge \u201ctoolbox\u201d with over 1,000 enzymes<\/strong>. When certain types of dietary fiber are broken down, substances are produced that in turn serve as food for other bacteria. This sharing of food is called cross-feeding: a single type of dietary fiber can thus feed a wide variety of bacterial species. <\/p>\n\n

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On average, however, women in Germany consume just 18 grams per day, and men 19 grams\u2014significantly less than the recommended 30 grams. This means that most of the bacteria in the gut are constantly starving. <\/p>\n<\/blockquote>\n\n

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What happens when you don’t get enough fiber?<\/h2>\n\n

First things first: Starvation can actually cause some of these bacterial species to disappear<\/strong>. The diversity of the gut microbiome decreases.<\/a>But it is precisely this diversity that is important, as it makes the microbiome more resilient<\/strong>. If a disruption occurs\u2014for example, due to the taking an antibiotic<\/a><\/strong>, a previously diverse microbiome can often recover more effectively. <\/p>\n\n

Without enough fiber, gut bacteria also produce fewer metabolic byproducts<\/strong>. These include short-chain fatty acids<\/a><\/strong>. These play key roles in the body. In particular, butyrate<\/a><\/strong> serves as an important energy source for the cells of the intestinal mucosa. In addition, short-chain fatty acids<\/strong> can have anti-inflammatory effects and even influence which genes are active in the body\u2019s cells. <\/p>\n\n

Without dietary fiber, the number of beneficial bacteria decreases<\/strong>, as do the metabolic byproducts they produce, which are important for a healthy body.<\/p>\n\n

But that’s not all: Not all bacteria can simply be starved out. Some switch to alternative food sources\u2014 at the expense of humans.<\/strong> <\/p>\n\n

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The Intestinal Protective Layer<\/h2>\n\n

The human intestine is lined with a mucous membrane<\/strong> that produces 10 L of mucus<\/strong> daily. This mucus forms a layer<\/strong> in the intestine, also known as the mucus layer<\/strong>. It performs important functions. One of them is that it acts as a kind of protective shield for the intestine. Like a moat, it keeps bacteria confined to the intestinal lumen\u2014that is, inside the intestine<\/strong>\u2014and away from the intestinal wall and the blood vessels behind it. <\/p>\n\n

The microbiome is important for human health, but only as long as it remains in balance. This means that the majority of bacteria remain in the large intestine<\/strong> and do not enter other parts of the body. To ensure this, the mucus layer there is divided into two layers. The dense inner layer, which acts like a moat, lies directly on the surface of the intestinal cells and is largely free of bacteria under normal conditions. The outer layer is looser and serves as a habitat for the gut bacteria, providing nourishment for some of them. Although the mucus layer consists mainly of water, its most important component is the mucin protein MUC2<\/strong>, to which numerous sugar chains are bound. These sugar chains serve as food for many gut bacteria. <\/p>\n\n

When the balance is healthy, the mucus layer performs two important functions: It provides a habitat and nourishment for the gut microbiome and protects the body by preventing bacteria from leaving the gut and entering other parts of the body.<\/p>\n\n

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When the Balance Is Upset<\/h2>\n\n

This delicate balance is disrupted when there is a lack of dietary fiber. The microbial Garden of Eden turns into a battlefield<\/strong> for nutrients<\/strong>. Those who can adapt best now have the advantage. In this case, there are two main groups. <\/p>\n\n

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The Mucus Specialists<\/h3>\n\n

The first group includes bacteria that feed on components of the intestinal mucus, such as Akkermansia muciniphila<\/em>. While their competitors in the gut run out of nutrients, their food source remains available to them. This gives them a competitive advantage. <\/p>\n\n

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The All-Around Talents<\/h3>\n\n

In addition to the \u201cmucus specialists,\u201d flexible bacterial species also benefit. They are the all-arounders among gut bacteria: not picky, but equipped with a variety of enzymes to break down different food sources. If dietary fiber is lacking, some of them can switch gears and feed on the sugar chains in the human mucus layer<\/strong> as well. <\/p>\n\n

Under these conditions, these two groups can multiply more rapidly. As a result, the mucus layer is increasingly used as a food source<\/strong>. It becomes thinner<\/strong> \u2014and the intestine\u2019s protective barrier weakens<\/strong>. <\/p>\n\n

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What does science say?<\/h2>\n\n

An impressive mouse study<\/strong> from 2016 demonstrated how a diet lacking in dietary fiber can affect the mucus layer. The researchers colonized germ-free mice\u2014that is, mice without their own microbiome\u2014with 14 bacterial species<\/strong> that are also found in the human gut. After these bacteria had established themselves in the gut, the mice were fed different diets: <\/p>\n\n