Today, there is a big debate about the right diet and the effect this or that diet has on the body. However, most of the scientific research on this topic is devoted to the study of the effect of individual nutrients under strictly controlled conditions. Therefore, the question remains what changes occur in the body of a person who starts to adhere to a healthy diet without changing other habits in his/her life. To answer this question, a group of scientists from the Theoretical and Applied Functional Genomics Laboratory at Novosibirsk State University, the “Atlas” Research Company, and ITMO University conducted a study in which 248 volunteers followed dietician's recommendations for two weeks to increase their intake of useful vegetable fibers and decrease "empty" calories.
Scientists were interested in the effect of the diet on the body in terms of changing the composition of the bacterial community (microbiota) in the volunteer’s intestines. To do this, each volunteer collected two samples of microbiota - before and after the change in diet. The samples were analyzed by metagenomics DNA sequencing. The results of this research were published in the scientific journal “Nutrients”.
Intestinal bacteria are mostly human symbionts. They protect us from infections, produce vitamins and essential oil for the intestinal cells, decompose complex polysaccharides, and participate in the formation of immunity. Disturbing the balance between the microbiota and the human body increases the number of opportunistic bacteria that cause inflammatory processes in the intestine and other health problems.
In the microbiota community, each microbe performs certain functions, a link in a complex metabolic network. The composition of nutrients coming in from the outside with food largely determines which microbes will gain a competitive advantage. On the other hand, health status also often affects the composition of the community. The presence of diseases such as type 2 diabetes, coronary heart disease, and inflammatory bowel disease can be predicted with relatively high accuracy by the human microbiota. The composition of the microbiota varies greatly among people and makes it possible to judge both their dietary preferences and their health status.
The presence of bacteria-fermenters, that convert complex polysaccharides into useful short-chain fatty acids in humans, is one of the important signs of a healthy microbiota. The study showed that by following the recommendations, there was a significant increase in the presence of these bacteria. This suggests that if a person changes their diet to a healthy one, within even just two weeks, a favorable effect on the microbiota will take place.
However, when there was an increase in the representation of microbes associated with a healthy organism, there was also a certain destabilization of the intestinal community. This was initially expressed in a slight decrease in its diversity. The more diverse the community, the more resistant it is to external influences, such as stress or antibiotics. The effect of reducing the diversity observed in the study was quite small. It appears this is related to the microbiota not having time to recover from the relatively rapid change in the diet.
Dmitry Alekseev, Senior Research Fellow at the NSU Theoretical and Applied Functional Genomics Laboratory, summarized their findings,
The research material provided the basis for the microbiota test, and the conclusion of the study is very practical. It is possible to improve the state of the intestine by increasing the amount of dietary fiber. In addition, it not only works in strict clinical settings, but at home.
Another interesting observation is that the microbiota reacted to the diet with varying strength for different people. In some people, there was a greater change to the composition of the community. The groups did not differ in the nature of nutrition consumed before the study or in the recommendations of the nutritionist, but they could be predicted with a high enough accuracy by the composition of their microbiota before the diet. This observation suggests that to increase the effectiveness of dietary recommendations, it is important to take into account not only the subject’s current nutrition, but the composition of its intestinal community.