If you want to lose weight, you often forget a crucial factor: the intestinal flora plays an important role in body weight. There are both bacterial strains in the gut that promote obesity and those that can make you slim.

If you want to lose weight, your intestinal flora is a close ally. The intestinal flora, experts speak of the “microbiome”, includes 100 trillion microorganisms, mainly bacteria, but also a few viruses and fungi. This diverse ecosystem in the digestive tract is not only important to our overall health, it also appears to affect our appetite and metabolism, and can even control our food preferences.

Numerous studies have now shown that the intestinal flora can have a major influence on body weight and the development of obesity and metabolic syndrome in this way.

Michaela Axt-Gadermann is a doctor and professor for health promotion in the “Integrative Health Promotion” course at Coburg University. She lives with her husband and children near Fulda. She has written numerous books on the subject of “intestines” and developed a licensed online nutrition coaching program (“Healthy with Intestines”) that is recognized by health insurance companies. You can also find more information on the “Slim with intestines” website.

In the mid-2000s, the suspicion first arose that – in addition to eating less and moving more – there must be other influencing factors that are turning our weight screw. At the time, American researchers found that mice without intestinal bacteria were leaner and had less body fat than mice that had a conventional microbiome.

If the germ-free rodents were now colonized with normal intestinal bacteria, they gained weight significantly within a very short time, the body fat value rose as well as the blood sugar level. The amazing thing: the mice stopped eating – in fact, they ate less.

Does this sound familiar to you too? Not only in mice, but also in humans there are those who are better “feed converters”. Those who find it difficult to maintain their weight, although they keep claiming that they don’t eat any more than others. Current microbiome research shows that this does not have to be a lame excuse for a lack of self-control, but that obesity can actually be caused by a changed intestinal flora.

American scientists around the biologist Jeffrey Gordon proved that there are clear differences in the composition of the intestinal flora between good and bad “feed converters”. Comparisons of the intestinal flora of obese mice and their lean siblings as well as of obese and lean human test subjects show that in obesity, among other things, the ratio of the two dominant bacterial strains Bacteroidetes and Firmicutes becomes imbalanced.

“Slim with intestines” by Michaela Axt-Gadermann

And this “thick intestinal flora” can even be “transplanted”. If slim mice were given the microbiome of overweight mice by means of fecal pellets, the previously thin animals gained significant weight within a very short time – despite being fed the same food. The microbiome and weight transfer even works between different species. If you transferred intestinal germs from human twin pairs, one of which was slim and the other tended to be overweight, to two groups of slim mice, the animals with the “fat” microbiome quickly became obese, the others ate the same amount of grains and still remained slim and slim .

Apparently, the mix of microbes in the gut is at least partly responsible for how well or poorly we use our food. The intestinal flora is now regarded as an important control point for energy production, metabolism and the formation of fat deposits. The group of Firmicutes bacteria, in particular, can extract considerable amounts of energy even from indigestible food components.

We now know that the intestinal flora of overweight people can produce many enzymes that break down polysaccharides that are actually indigestible for humans and in this way “help” us to gain a lot of energy from little food. In times of famine and bad harvests, this is a clear survival advantage – but today it is rather undesirable.

If the number of Firmicutes increases, more carbohydrates and thus more calories are absorbed by the intestinal mucosa. Excess energy is then sent to the liver and eventually converted into fat and deposited on the abdomen, buttocks and hips. If the number of these “moppel bacteria” increases by only 20 percent, then around 150 additional kilocalories are absorbed into the body every day. That doesn’t sound like much at first, but over the course of a year it adds up to around eight extra kilos!

But there are other characteristics that distinguish a “thick” from a “slender” microbiome. People with weight problems usually have too little variety (diversity) of the intestinal flora, i.e. the composition of the bacterial community is monotonous and they lack numerous weight-regulating bacteria or these are underrepresented.

Many overweight people have a lack of bifidobacteria in their intestines and there are also no germs with nice names like “Faecalbacterium prausnitzii” or “Akkermansia muciniphilia”. Recent studies have linked high levels of these bacteria to low body weight, lower body fat percentage, lower risk of diabetes and metabolic syndrome.

Suspicion quickly falls on our modern Western lifestyle with a low-fiber and high-fat diet. Because the slimming germs in the intestines need special plant fibers, so-called prebiotics, in order to grow and thrive. These are contained, among other things, in legumes, onion vegetables, oat flakes, endive salad, asparagus and leeks, i.e. foods that you usually look for in vain in the fast food kitchen.

Unbalanced diets such as strict low-carb diets also seem to have a negative impact on the diversity of the microbiome. Apparently, an unbalanced, low-fiber diet causes a change in the intestinal flora, which then subsequently draws more calories from the food.

But the microbiome researchers have also targeted antibiotics, because nothing disrupts the healthy microbiome as lastingly as these drugs. It has been known from cattle breeding since the 1940s that antibiotics lead to faster master sequences and that animals given antibiotics weigh more with less feed.

Similar antibiotic effects have now been demonstrated in humans: Babies who received antibiotics in the first six months of life were more often overweight at the age of three and when they started school. It is similar for adults – despite their much more stable intestinal flora. For them, too, most studies indicate that longer antibiotic therapies sometimes lead to enormous weight gain.

The medical history provides indications that the microbiome could play a role. If antibiotics were often taken in the past, there is a higher risk that the intestinal flora has not fully recovered from them and is now driving the weight up.

Weight gain usually does not start immediately after the last antibiotic pill, but develops gradually over the following months or within a year. Due to the large time difference, however, the connections are often not perceived.

If there are also intestinal problems such as abdominal pain, flatulence, irregular bowel movements or the like, this also indicates that a dysbiosis could be partly responsible for the fat deposits.

With the help of a microbiome analysis, changes in the microbiome that are associated with obesity can be detected. The biodiversity of the microbiome, which is important for a slim figure, can thus be determined, as can the balance of the individual trunks with respect to one another.

In addition to determining important bacteria such as Akkermansia muciniphilia, Faecalbacterium prausnitzii, bifidobacteria and butyrate-forming bacteria, the Firmicutes-Bacteroidetes index is also of interest. This value shows the ratio of the “moppel bacteria” Firmicutes to the rank-and-slender germs Bacteroidetes and seems to be a marker with which one can estimate whether one’s own microbiome could be responsible for weight problems.

Nutrition forms an important basis for the development of a healthy microbiome. If you want to change your gut flora, you have to change your eating habits, but that doesn’t mean meals will be boring, monotonous, or less enjoyable.

Foods rich in prebiotics are suitable for promoting the growth of beneficial bacteria. Prebiotics are indigestible fibers that are available in the colon as “food” for the microbiome. They are contained in oatmeal, cranberries, apples, almonds, leeks, garlic, onions, black salsify, Jerusalem artichoke, asparagus and other foods.

Potatoes, rice and pasta also contain certain prebiotics when they have cooled after cooking. Potato, rice or pasta salad are good alternatives. Beneficial effects on the intestinal flora have also been demonstrated for stimulants such as coffee, dark chocolate, green tea and even red wine. In addition, you can eat fermented foods such as sauerkraut, kefir or yoghurt more frequently. These foods provide gut-friendly lactic acid bacteria.

According to studies, the effects on weight can be increased with dietary supplements that contain suitable bacteria (lactic acid bacteria, bifidobacteria, streptococci) and prebiotic fiber.

Numerous studies show that probiotic, i.e. microorganisms that promote intestinal health, can support weight loss – if you take the right bacteria. But be careful here, because some probiotics can even pack extra pounds on your hips.

Studies have not been able to demonstrate favorable effects on weight, body fat percentage and waist circumference for all probiotics, although the study situation is not always clear. Measurable success in terms of waist circumference, body fat percentage, weight or metabolic parameters can be achieved, among other things, by administering the lactic acid bacteria Lactobacillus gasseri, Lactobacillus curvatum and Lactobacillus plantarum or Lactobacillus casei. In one study, however, women benefited more from Lactobacillus rhamnosus than men.

Since bifidobacteria have also been able to support weight loss in studies and are often missing in the intestines of people with weight problems, it could make sense to also integrate these probiotic bacteria into an intestinal diet. Studies have shown effects for different bifido strains such as B. longum or B. adolescentis.

But there is evidence that not all lactic acid bacteria have the same beneficial effect on our weight. A look at the bacterial strains contained can be helpful, because these determine in which direction the weight may move.

This is shown, among other things, by a US study. Scientists from the Department of Preventive Medicine at the University of Southern California, Los Angeles, hoped to improve the weight problems of overweight young people with the help of a high-dose probiotic preparation. But the results were disappointing. After four months of regular intake, the young people had gained significant weight.

This may be due to the fact that the preparation also contained “fatty” probiotic bacteria. Among other things, this preparation contained Lactobacillus acidophilus. Other studies have already shown that this strain of bacteria leads to significant weight gain in humans and animals.