Undersupply of fiber: Western eating habits reduce valuable intestinal bacteria

Undersupply of fiber: Western eating habits reduce valuable intestinal bacteria

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A low-fiber diet causes considerable damage to the intestinal flora
The variety of beneficial intestinal bacteria can be irreversibly damaged by the typical western diet. The low proportion of fiber and microbiota accessible carbohydrates in the food of modern industrial nations leads to an increasing loss of intestinal bacteria from generation to generation, report US researchers of the Stanford University School of Medicine. This results in corresponding impairments of the intestinal flora and far-reaching negative consequences for the entire organism.

The team led by Professor Justin Sonnenburg from the Stanford University School of Medicine was able to use mice to prove that the low-fiber diet has a direct impact on the intestinal flora and that irreversible changes occur across the different generations of the animals. After four generations on a low-fiber diet, the researchers said that almost three quarters of the beneficial intestinal bacteria had disappeared. The scientists have published their results in the specialist journal "Nature".

Thousands of different types of bacteria inhabit the colon of every healthy individual and "we would have difficulties without living", emphasizes Professor Sonnenburg. According to the microbiologist, the intestinal bacteria help "ward off pathogens, they train the immune system and even influence the development of our tissues." The bacteria also play a key role in the utilization of nutrients.

The individual intestinal bacteria population is influenced by various factors, whereby the intestinal bacteria of the family and especially the mother are of primary importance. They are transmitted to newborn children and babies.

Changes in the intestinal flora in the course of life
However, the intestinal flora changes during life. For example, taking antibiotics can cause significant damage to the intestinal bacteria. "Numerous factors, including the widespread use of antibiotics, the increase in Caesarean sections and less frequent breastfeeding," have led to an impoverishment of the intestinal flora, explains Erica Sonnenburg, lead author of the study (and wife of Professor Justin Sonnenburg).

The diet is also of particular relevance for the biodiversity of the intestinal bacteria. The scientists therefore wondered what impact the big difference in fiber intake between traditional and modern populations has on the intestinal bacteria.

Low fiber in modern foods
The spread of almost fiber-free, processed food products since the middle of the 20th century has led to a decline in fiber intake in industrial societies to around 15 grams per day, report Professor Sonnenburg and colleagues. This is "less than a tenth of the fiber intake of today's societies of hunter-gatherers or rural-agricultural populations, whose living conditions and food intake are probably most similar to those of our common human ancestors," explains Professor Justin Sonnenburg.

Practically all health experts agree that such low-fiber diets are not recommended from a health point of view. Also because the fiber, which cannot be digested by human enzymes, is the main source of nutrition for the intestinal bacteria.

Intestinal bacteria profiles in mice were examined
In their study, the US scientists used mice to investigate the effects of a low-fiber diet on the intestinal bacteria. Young laboratory mice, which were specially bred under aseptic conditions and therefore had viscera without any microbial colonization, received microbes from a human donor, so that they developed an appropriate intestinal flora.

The mice were then divided into two groups, one group receiving a high-fiber diet and the other group a diet high in protein, fat and calories, but practically without fiber. During the experiments, the researchers examined the faecal samples of the animals and thus determined the profiles of the intestinal bacteria. The bacterial profiles did not initially differ in either group. However, massive changes could be identified within a few weeks, reports Professor Justin Sonnenburg.

A lot of bacteria have already disappeared after a few weeks
According to the researchers, the mice in the low-fiber group showed significantly fewer types of bacteria in the intestine after around six weeks than the animals in the control group. In more than half of the bacterial species, the occurrence had decreased by over 75 percent and many species seemed to have completely disappeared, report Professor Sonnenburg and colleagues. After a seven-week trial period, the mice's diet was switched back to a high-fiber diet for four weeks. Although the intestinal bacteria profiles could be partially recovered, this recovery was only possible to a limited extent, according to the scientists.

"A third of the original species never returned completely, despite the high-fiber diet," the US researchers said in the Stanford University School of Medicine press release.

Diversity of the intestinal bacteria decreases with every generation
However, according to the scientists, the real surprise was the cross-generational effect in the development of the intestinal flora. The low-fiber diet caused a declining variety of intestinal bacteria in each subsequent generation of mice. In the fourth generation, almost three quarters of the original types of bacteria used in the experimental animals had disappeared. Even if these mice were put on a high-fiber diet, more than two-thirds of the bacterial species remained irretrievably wiped out. This amounts to an extinction of the species in the fourth generation of a low-fiber diet.

Dietary habits in modern industrialized nations could therefore irreversibly wipe out numerous beneficial intestinal bacteria in future generations. So far, however, it has been difficult to assess the consequences for human health. Experts believe that symptoms such as a bloated stomach or persistent abdominal pain are the first signs of a disturbed intestinal flora. In the long term, the negative effects will increase significantly across generations, according to the researchers. (fp)

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