Decades-old assumption about microbiota revisited.
It’s often said that the bacteria and other microbes in our body outnumber our own cells by about ten to one. That’s a myth that should be forgotten, say researchers in Israel and Canada. The ratio between resident microbes and human cells is more likely to be one-to-one, they calculate.
A ‘reference man’ (one who is 70 kilograms, 20–30 years old and 1.7 metres tall) contains on average about 30 trillion human cells and 39 trillion bacteria, say Ron Milo and Ron Sender at the Weizmann Institute of Science in Rehovot, Israel, and Shai Fuchs at the Hospital for Sick Children in Toronto, Canada.
Those numbers are approximate — another person might have half as many or twice as many bacteria, for example — but far from the 10:1 ratio commonly assumed.
Remember Pig-Pen? The little kid from Charles Schulz’s Peanuts cartoons who walked around in a cloud of dirt? Well, the human body does spew a cloud, but instead of dirt it contains millions of microorganisms.
“It turns out that that kid is all of us,” says James Meadow, a microbial ecologist who led research about the microbes shadowing us during postdoctoral work at the University of Oregon. “It’s just a microscopic cloud that’s really hard to see.”
The findings from Meadow and his colleagues were published Tuesday in the journal PeerJ.
Each of us carries around millions of microorganisms – including bacteria, fungi and viruses — on the inner and outer surfaces of our bodies. Most of them aren’t dangerous. In fact, growing evidence indicates that they help us in lots of ways. Scientists call this collection of organisms our microbiome.
Mice fed a diet high in saturated fat show shifts in their gut microbes and develop obesity-related inflammation.
The types of lipids mice consume affect the composition of their gut microbiota, which influences whether the animals develop obesity-related inflammation, according to a study published today (August 27) in Cell Metabolism. Mice fed a high-lard diet for 11 weeks developed signs of metabolic disease, while mice fed fish oil remained healthy. When the researchers transplanted gut microbes from fish oil-fed mice to antibiotic-treated mice and then subsequently fed the animals lard, the mice were protected from the typical unhealthy effects of the saturated fat.
“This paper, which had nicely controlled conditions, demonstrated that type of fat is really important for shaping microbial communities and their functional dynamics, which in turn impact our health,” said Vanessa Leone, a postdoc studying host-microbe interactions at the University of Chicago who was not involved in the study.
Scientists don’t know what causes rheumatoid arthritis, but many suspect that the microbiome—the bacteria that live in our gastrointestinal tracts—may be to blame.
Several recent studies have found intriguing links between gut microbes, rheumatoid arthritis, and other diseases in which the body’s immune system goes awry and attacks its own tissue.
While it’s long been said that “you are what you eat,” a more accurate description might be “you are what your microbes eat.” There are more bacteria and other microorganisms in your body than there are human cells, and your unique microbial community is constantly changing in response to your environment.
In fact, a new diet can rapidly reshape the microbes in your gut, which has implications not only for your digestive health but far beyond this to your weight, risk of chronic diseases, and more. According to research published in the journal Nature, such changes may occur in as little as one day:
“… [S]hort-term consumption of diets composed entirely of animal or plant products alters microbial community structure and overwhelms inter-individual differences in microbial gene expression.
The animal-based diet increased the abundance of bile-tolerant microorganisms (Alistipes, Bilophila, and Bacteroides) and decreased the levels of Firmicutes that metabolize dietary plant polysaccharides.”
Gut microbes known as Firmicutes have been detected in higher numbers in obese individuals, who also may have 90 percent less of a bacteria called bacteroidetes than lean people.
It’s been suggested that altering gut bacteria could therefore play a role in obesity, although a computer analysis led by Katherine Pollard, a biostatistics professor at the University of California, San Francisco suggests it’s much more complex than that.