More Obesity-Related Bacteria

Angel's and Devil's Food Cake“Related” is such a nice neutral word, and nowhere is it needed more than in discussion of the microbiome, the interior universe where exploration is just beginning.

Michael Pollan helps readers understand why the microbiome is so fascinating. Fecal transplants, for instance, are no laughing matter. The technique could save some of the 14,000 Americans who die each year of C difficile infection. While this knowledge has no direct relationship to obesity, it helps us to realize that when “good bugs” are sent in to save the day, they can be potent.

Even the idea of good bugs is misleading, because apparently each human is landlord to a boardinghouse full of road company actors. Some of our tiny tenants can play the full range of roles, from villain to hero to victim to neutral bystander.

The link between two phenomena might be statistically noteworthy, but in the realm of pure science, it is always a mistake to draw premature conclusions. For example, a Canadian study found that obesity correlates with daycare. Ideally, this news would inspire a search for the reason for the correlation, so the daycare paradigm could be fine-tuned. We should not assume that daycare is evil and all such establishments must be immediately suppressed. Trying to connect the dots is a perilous undertaking, fraught with complications.

Pollan notes that “obese mice transplanted with the intestinal community of lean mice lose weight and vice versa.” He reminds us that we don’t know why. He speaks of a similar experiment in the Netherlands, this one with human subjects:

When the contents of a lean donor’s microbiota were transferred to the guts of male patients with metabolic syndrome, the researchers found striking improvements in the recipients’ sensitivity to insulin, an important marker for metabolic health. Somehow, the gut microbes were influencing the patients’ metabolisms.


Bifidobacteria belong to a subgroup pretty far down the taxonomical ladder, but they are one of the most prominent inhabitants of the human large intestine. In “Introduction to Intestinal Microbiota,” Diana Di Gioia wrote:

Human milk favours colonization by bifidobacteria. Bifidobacteria are dominant in faeces of breast-fed infants, whereas Bacteroides spp. are dominant in formula-fed infants.

Childhood Obesity News has mentioned Bacteroides, which have something to do with mollifying lab mice out of a tendency toward repetitive and obsessive behavior. If properly harnessed, they might put a lid on compulsive eating among humans. In which case, having a lot of Bacteroides would appear to be a good thing. But just because it appears to promote the flourishing of Bacteroides, should we assume no harm is done by feeding canned formula to infants?

Getting back to bifidobacteria, there is very strong evidence that breastfeeding reduces the risk of obesity and diabetes in kids. But how and why? We know, at this point, that some things correlate. A study published a while back in the American Journal of Clinical Nutrition found that…

…babies with high numbers of bifidobacteria…and low numbers of Staphylococcus aureus, appeared to be protected from excess weight gain. This may also be one reason why breast-fed babies have a lower risk of obesity, as bifidobacteria flourish in the guts of breast-fed babies.

Dr. Noel T. Mueller says:

Human breast milk contains oligosaccharides, which are a type of complex carbohydrate that act as a prebiotic by cultivating the growth of bifidobacteria in the infant gut. As vaginal delivery is one of the primary avenues by which bifidobacteria colonizes the infant gut, the prebiotic benefits of human breast milk may be modified by mode of delivery, but this hypothesis remains to be tested.

And so it goes. The field is littered with hypothesis that remain to be tested. For some researchers, the prize at the end of the road is the Grand Unified Theory of Everything. Others just take it one day at a time.

Your responses and feedback are welcome!

Source: “Some of My Best Friends Are Germs,”, 05/15/13
Source: “Introduction to intestinal microbiota,” Pweb, 06/28/11
Source: “Early differences in fecal microbiota composition in children may predict overweight,”, 2008
Source: “The Gut Microbiome and Childhood Obesity: Connecting the Dots,”, June 2015

Image by Alex Gorzen

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