Study of human identical twins and genetically altered mice gut bacteria, reveals that after ingesting fermented milk-products, carbohydrate digestion increases.
By Leah Farrell
The human body is made up of about 100 trillion cells and also contains about ten times as many microorganisms in their intestinal tract (1). These gut flora, or intestinal microbiota, aid humans in their digestion of certain large polysaccharides, sugars, because they produce enzymes that humans are unable to produce themselves (2). Gut flora have an estimated 100 times as many genes as there are in the human genome and this allows them to produce those enzymes we are unable to (1). Without these microorganisms humans wouldn’t be able to digest certain starches, fiber, and oligosaccharides (2). Nathan McNulty and colleagues conducted an experiment to test the effects of ingesting fermented milk products, dairy products, that only contained five well documented species of bacteria on the normal flora of identical twins as well as on genetically altered mice (3). The goal of this experiment was to understand the genetic and nutritional factors that allow human’s mutually beneficial relationship with microbes to occur (3).
The diversity of the microorganisms found in the human gut is due to a combination of human genes, environmental factors, ingestion of antibiotics, and diet (3). These factors are why it is difficult to conduct studies on the gut of humans because each person’s gut may contain completely different species of flora from one day to the next. Monozygotic, identical, twins were chosen as good test subjects because they have the same genes and experienced similar dietary factors early on in life that no two other individuals experienced (3). Genetically altered mice were created for this experiment to contain a model of microorganisms that represent the model of human gut flora (3). One group of mice was feed the same five bacteria that the human participants ingested only once while a second group of mice was fed the five bacteria twice more after the initial feeding.
Seven adult female pairs of identical twins agreed to be participants in this study. The women did not consume any antibiotics six months before the experiment, none had a history of gastrointestinal diseases, none consumed probiotics, none had a history of gluten allergies, and none of the women were vegans or lacto-vegetarians. Four weeks before these women began ingesting the diary products containing the five strains of bacteria three stool samples were collected to test their normal levels of gut flora. At week four each participant was shipped their first sample of fresh diary product; a new shipment came every two weeks and four stool samples were collected during this time. Two more samples were collected after week twelve when the women stopped consuming the altered diary product to test the levels of gut flora.
No significant change in the variety of species of gut flora occurred in both the mouse and human participants. Of the five species ingested B. Animalis subsp. lactis was present in the highest levels in the gut flora in mice and human. The most note worthy observation from this experiment is that all participants exhibited an increased ability to digest carbohydrates while they were consuming the five strains of bacteria, specifically B. Animalis subsp. lactis. The normal model of human flora responded to the introduction of the five strains of bacteria by turning on genes that were not turned on in the absence of the new five. These newly turned on genes enabled both animal and human participants to ferment carbohydrates into propionate, a molecule that can be converted into glucose and therefore absorbed and digested (3). This experiment is a good example of how manipulating the gut flora in humans can increase our ability to digest foods and absorb nutrients that we were previously unable to enhancing our overall health.
1. Bjorksten B, Sepp E, Julge K, Voor T, Mikelsaar M. 2001. Allergy development and the intestinal microflora during the first year of life. J. Allergy Clin. Immunol. Vol 108: 516-20.
2. Guarner F, Malagelada JR. 2003. Gut flora in health and disease. The Lancet. Vol 361: 512-519.
3. McNulty, Nathan P., et ali. 2011. The Impact of a Consortium of Fermented Milk Strains on the Gut Microbiome of Gnotobiotic Mice and Monozygotic Twins. Sci Transl Med.