Gutmicrobiota play a pivotal role in energy balance and contribute to development of obesity. A scientific microcosm with broad public health implications.

Darmbakterien und Adipositas / GUT MICROBES and Obesity => read the following article in German as it appeared in print in the daily newspaper “DIE WELT”.

Here is an approximate translation into English:

Gut Microbiome, Nutrition, and the Link with Obesity and Cancer


by Karen Dente-Mouradian, M.D.

In medicine today one refers to the totality of the intestinal microbes as the microbiome, as opposed to the intestinal flora, which alludes more to the plant world. The living microbiome consists of the entirety of the microbiological bacterial community: there is a tremendous diversity of species, with trillions of different intestinal bacteria thought to be colonizing the human gut. This is ten times the number of the cells contained in the human body. On the genetic level, this translates to a scale of about 100 times more microbial genes in the intestine alone, than are found in all human cells. Many of these genes play a crucial role in energy metabolism. Gut microbes also are thought to have an important effect on immune regulation, the prevention of malignant tumors as well as the preservation of colonic mucosa cells.

Nine of 70 bacterial strains have been defined that are known to live in the human intestine. So-called Firmicutes and Bacteroidetes are the two most common groups of bacteria defined in the human gut. These bacteria, present mostly in the colon, use special enzymes that digest fermentable fibers that man alone is unable to digest,  and assist in breaking these nutritents down into usable energy substrates. Fermentable fibers are often found in foods such as oat bran or beetroot. Whether these bacteria benefit themselves and live in symbiotic mutualism with us human hosts, or are rather to be regarded as neutral commensalists that do not draw any benefit for themselves is subject to debate among biological ecologists.

Analyzing the composition of the human microbiome along with the impact on pathological development is currently beginning to draw some renewed interest as a major focus of research in microbiology, especially given the the growing tide of the obesity epidemic worldwide,  in conjunction, also, with the understanding of antibiotics’ bacteria-eradicating effects on the intestinal flora. Of course the food industry has its self-interested role in supporting the capitalization of food products containing so-called pre-biotics and probiotics that seek to supplement foods with either fermentable fibers (pre-biotics) that stimulate gut microbes already present or as a source of supplemental live bacteria that can colonize the gut (probiotics). And smaller as well as large global corporations have a very vested interest in promoting researchers and their research in this area.

“Determining the exact composition of the microflora, and finding an association with either healthy or overweight people is currently a very hot research topic,” said Walter Gall, director of clinical study Metabolon Inc., USA. The biotech company based in North Carolina intends to market diagnostic tests that will detect early metabolic changes seen in individuals with pre-diabetic conditions – even before the onset of typical type-2-diabetes, and its associated insulin resistance.

The picture of the composition of the intestinal flora has changed dramatically since the introduction of molecular techniques. The difficulty in the study of bacterial microbiome has always been the lack of culturability of gut microbes. More than 50 percent of the human gut bacteria cannot be grown to the size of countable colonies in any culture medium  – and thus can’t be directly determined. Today, with the advent of genetic analyses using so-called polymerase chain reaction (PCR) techniques, this has changed. However, these genetic tests serve to confirm tests using basic colony culture determined from stool samples collected from the study subjects.

Studies in this area are not yet performed on a sufficient scale to give a definitive indication of the composition of various strains of bacteria in obese persons. The journal “Nature” published a key study on this a few years ago, and concluded that overweight people have a reduced biodiversity in the composition of their gut microbes. Above all, the proportion of so-called Bacteroidetes compared to the Firmicutes groups seen to be increased.

But this “Nature” journal study result stood in contrast to the results of other studies, that found an inverse relationship between the two groups of bacteria to one another.  A recent study of 26 obese and 27 non-obese children, whose results were recently presented at the 19th European Congress on Obesity in Lyon, France, and suggested an influence of diet composition on the distribution pattern of intestinal bacterial species in obese and lean children.  Obese childern were found to have more Firmicutes bacteria compared to Bacteroidetes bacteria. This was found to be linked to a deficiency of protein intake in the diet, with no statistically significant link found with carbohydrates. Liene Bervoets, PhD, who has researched on the subject at the University of Antwerp and presented her research findings, said: “It is interesting to observe that the gut microbiota appear to play a role in the development of obesity in children; when comparing obese and lean children, we can observe very significant differences.”

The mutual influence of intestinal flora and body weight is best understood in the context of energy absorption. It is believed that the microbiome contributes to the long-term positive energy balance in humans. An animal experiment in which the gut flora of obese mice was transplanted in microbe-free mice was able to confirm this. The study looked at mice that gained weight despite a reduced food intake, which suggests it to be more likely for there to be a central role played by the microbiome in weight regulation, regardless of the actual composition of the diet. But this causality has yet to be confirmed in larger studies in humans.

Diet to seem to play a crucial role in the interplay between microbes and excessive fat deposition in individuals receiving poor nutrition. Nutritionists largely agree, for example, that easily fermentable fiber-rich foods such as oat bran and pectin-containing foods such as beetroot, also found in various types of fruit, can exert a preventive effect on the process of fat accumulation in the body. The above-mentioned nutrients cannot be decomposed in the first section of the human intestine. The first segment of the human gut is reponsible, rather,  for the absorption of simple carbohydrates. Nutrients that eventually end up in the large intestine are usually those that will be broken down in a segment of the gut where there are more microorganisms such as the Firmicutes bacteria, which contain the crucial fermenting enzymes to draw energy out of these fibers. These bacteria metabolize the nutrients and generate more energy in the form of short-chain fatty acids. Resulting metabolic intermediates such as butyric acid  are especially important in the colon for the preservation of life the intestinal cell walls. But a build-up of these substrates in the blood is currently also being discussed as an indication of pre-diabetes. In the colon, however, these butyrates are thought to help to prevent the development of colon cancer. They continue to play a role in secreting certain satiety hormones, and act as a natural satiety signal to the brain.

In 2003 the World Health Organization had announced that a diet rich in fiber is the best and only proven effective strategy to prevent obesity, and metabolic diseases such as type-2 diabetes. The sugar molecules found in low glycemic index fiber-rich nutrients are absorbed in the later part of the intestinal tract so that blood sugar levels rise more slowly. An oversupply of sugar damages the body especially when sugar circulates at high spikes and levels in the blood and is failed to be incorporated inside the cells – as is seen in the onset of insulin resistance in type 2 diabetes. The damage is often insidious and can affect the tiniest of blood vessels in many organs, including kidneys, eyes, and the entire circulatory system including the coronary vessels of the heart.

The interplay between nutrients and bacteria is complex, and will require further larger studies to help establish a strong, valid theory of the gut microbiome’s exact role in energy extraction and its contribution to obesity and diabetes, in relation to diet. How specific gut bacteria precisely contribute to the development of diseases such as obesity, diabetes and cancer, remains nebulous, or anybody’s best guess, but the current thinking in the research community interested in nutrition, environmental microbial ecology as it relates to human health is that these trillions of gut microbes play an important and central role in the development of these  non-communicable diseases that the W.H.O. has set a goal of combatting in the coming decade in developing and non-developing nations worldwide.


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