If you’re a regular reader of our weekly posts (and thank you so much if you are—it makes our very microbes merry) you’ll perhaps recall that last week we time-traveled back to the 13th century and Genghis Khan to explore and thoroughly debunk the Five Second Rule.
This week, however, we’d like to bring you back up-to-date by reporting on a fascinating study that was published on Monday (9/26/16) in the journal Genome Biology.
Its authors suggest that a dangerous kind of obesity may be associated with bacteria in the microbiome that can be “inherited.”
And, the paper’s authors say, this may partly explain why obesity can sometimes seem to run in families.
Like many studies, the story is slightly complicated, so we’ll do our best to interpret what it tells us, beginning with twins.
The focus of the study (led by scientists at King’s College London, with a team that also included researchers in the USA, Germany, and Belgium) was on approximately 1,800 pairs of twins, around 1,000 of whom were identical (monozygotic) and 800 who were fraternal, or non-identical (dizygotic).
They therefore studied 3,600 individuals in total, all members of a British twin registry known as Twins UK, where twins have volunteered to take part in scientific studies.
So-called twin studies are a staple of many areas of human science because identical twins not only look alike but are also almost (but not totally) genetically identical.
In many instances, twins are raised together, whether or not they are identical, so they develop in the same environment—with the same diet, for example.
Studying both monozygotic and dizygotic twins therefore enables researchers to investigate variances that may be associated with genetic similarities or differences.
In the research reported yesterday, the scientists set out to do two things:
They examined the bacterial composition of stool samples taken from the participants using 16S rRNA sequencing, the same methodology we use at uBiome, and they measured something called abdominal visceral fat, which health professionals regard as dangerous.
Unlike subcutaneous fat, which is, for example, what generally makes up a belly, visceral fat is buried deep in the body.
It often tends to be wrapped around major organs such as the kidneys, pancreas, and liver.
And experts say the reason it’s so hazardous is that it’s associated with a host of conditions, including coronary heart disease, cancer, stroke, dementia, and depression.
Unlike BMI— an inexact rating of obesity—visceral fat measurement is much more revealing, and it is determined using a process called Dual X-Ray Absorptiometry (DXA), which can divide soft tissue into lean and fat.
Previous work by some of the same researchers showed that the microbiomes of monozygotic twins are more similar than those of dizygotic twins, suggesting that, to some degree at least, we inherit the type of bacteria that inhabit our gut.
Until recently, it was believed that babies were born with a “sterile” gut, but we now know this isn’t so. They’re born with a smattering of bugs acquired while in the womb.
Probably, though, both monozygotic and dizygotic twins receive the same bacteria in utero.
Maybe it’s the genetic makeup of an individual that somehow either “attracts” or “repels” certain types of bacteria?
Or perhaps our genes somehow influence what we choose to eat in the first place?
It’s not easy to know, but further research may cast more light on the mechanisms involved.
But what were the two important takeaways from yesterday’s paper?
The first was that it confirmed the association between obesity and lower diversity in the fecal microbiome. The authors noted that obese individuals appeared to have fewer different bacterial species in their guts than lean individuals.
Secondly, the research identified a pretty big genetic component to visceral fat mass: heritability was responsible for 0.7 (or 70%) of the variance, so at least to some degree, it seems that you have a genetic predisposition to end up with a similar body shape to your parents, and this may be partly due to having a microbiome like Mom (or Dad).
As for increasing bacterial diversity, the study’s lead researcher, Dr. Michelle Beaumont, suggests that eating a broadly varied diet can help.
Five a day is good.
Varying your five a day is even better.