Scientists say that around a quarter of the population, particularly those who are obese, have 40% less intestinal bacteria than needed to maintain good health, according to a study published in the journal Nature.
Researchers from Europe conducted a genetic analysis on human gut microbial composition on 292 people from Denmark. Of the subjects, 169 were obese and 123 were at a normal, healthy weight.
Results of the analysis revealed that a quarter of the participants had 40% fewer gut bacteria genes and correspondingly less bacteria than average.
Oluf Pedersen, professor and scientific director at the Faculty of Health and Medical Sciences at the University of Copenhagen, says:
"Not only has this quarter fewer intestinal bacteria, but they also have reduced bacterial diversity and they harbor more bacteria causing a low-grade inflammation of the body."
The researchers explain that our gut needs a wide diversity of intestinal bacteria in order for us to maintain our health.
Gut bacteria strengthens our immune system, produces vital vitamins and communicates with the nerve cells and hormone-producing cells within the intestinal system. The researchers add that gut bacteria also produces a variety of "bioactive substances" which enter the bloodstream, affecting our biology.
Low gut bacteria more prominent in obese
Although the findings of the analysis revealed that all participants exhibited reduced gut bacteria, this appeared more prominent in those who were obese.
Prof. Pedersen explains:
"Our study shows that people having few and less diverse intestinal bacteria are more obese than the rest.
They have a preponderance of bacteria which exhibit the potential to cause mild inflammation in the digestive tract and in the entire body, which is reflected in blood samples that reveal a state of chronic inflammation, which we know from other studies to affect metabolism and increase the risk of type 2 diabetes and cardiovascular diseases."
The researchers note that the group who had less intestinal bacteria who were already obese, were more likely to gain weight in the years to come. But they say they do not know whether lack of intestinal bacteria is the cause of obesity, or whether obesity is the cause of less intestinal bacteria.
Previous research has also suggested a link between gut bacteria and obesity. A study from the Cedars-Sinai Medical Center in Los Angeles found that the presence of certain bacteria in the gut causes it to take more calories from food, therefore leading to weight gain.
Diet 'may help boost' gut bacteria
Although the study authors are yet to explain fully why some people have less intestinal bacteria compared with others, they believe our diet may be a contributing factor.
They point to a recent study from a French research team, which revealed that a group of overweight participants who followed a low-fat diet for 6 weeks and who had less intestinal bacteria at the beginning of the diet, showed an increase in gut bacteria in both variety and amount.
"This indicates that you can repair some of the damage to your gut bacteria simply by changing your dietary habits," adds Prof. Pederson.
"Our intestinal bacteria are actually to be considered an organ just like our heart and brain, and the presence of health-promoting bacteria must therefore be cared for in the best way possible. Over the next years, we will be gathering more knowledge of how best to do this."
Further research for 'environmental factors'
The study authors note that further research is to be carried out in order to determine whether environmental factors linked with gut bacteria may have an effect on our health and risk of disease.
"At present we cannot do anything about our own DNA, individual variation in which also plays a crucial role in susceptibility for lifestyle diseases," says Prof. Pederson.
"But thanks to the new gut microbiota research, we now can start exploring interactions between host genetics and the gut bacteria-related environment which we may be able to change. That is why it is so exciting for us scientist within this research field - the possibilities are huge."
He adds that in the long-term, the research team would like to pinpoint any naturally occurring gut bacteria that could produce "appetite-inhibiting bioactive substances" and find new interventions that could prevent obesity and type 2 diabetes.