We know a few major reasons, such as unfortunate genes, nutrient-poor/high-calorie diets, and sedentary lifestyles.
But these factors don’t explain everything, and not everyone who has one or more develops a metabolic disorder.
Conversely, some people lacking these risks still develop a metabolic disorder, for reasons that have been unclear.
A landmark study now links the risk for metabolic disorders – obesity, cardiovascular disease, and diabetes – to a shortage of friendly intestinal bacteria (Le Chatelier E et al. 2013).
Its startling findings show that about one in four Danes have about one-quarter fewer friendly intestinal bacteria than average.
These unlucky people also have reduced bacterial diversity and harbor more bacterial strains known to cause low-grade inflammation in the body.
We don't yet know whether this finding applies to all ethnic groups, but it seems safe to presume that it is not limited to Danish people.
While these remarkable findings are bad news for some folks, they also clarify the picture of human health and point to potential solutions ... see “Low-fat diet raised bacteria counts in overweight people”, below.
Before we examine the landmark new study in more detail, let's review the basics of human gut bacteria .. also known as the microflora or microbiota.
Your gut resembles a rainforest
The human microflora resembles a tropical rainforest, said lead author Oluf Pedersen of the University of Copenhagen.
Like a rainforest, our bodies do best when our gut microflora exhibits a high degree of biodiversity. Accordingly, lack of microfloral diversity is a cause for concern.
Other scientists liken our intestinal bacteria to a complex organ, and it’s becoming clearer that we can’t thrive fully when our microflora is underpopulated, overly homogenous, or skewed in unhealthful directions.
The bacteria living in us produce vitamins, mature and strengthen the immune system, and communicate with our nerve and hormone-producing cells in ways that can profoundly affect health.
In addition to B vitamins and other nutrients, gut bacteria also produce a wealth of substances that penetrate to the bloodstream and affect our bodies in countless ways.
These include the chemicals produced when gut bacteria metabolize the polyphenol “antioxidants” in plant foods.
Polyphenols occur in all in fruits and vegetables – especially colorful ones – with berries, plums, cocoa, tea, onions, and leafy greens ranking high. See “Plant antioxidants interact with gut microflora, beneficially”, below.
Unlucky belly-bug profiles promote obesity, cardiovascular, and diabetes
Our intestines play host to trillions of bacteria and other microbes … the diverse, microscopic ecosystem that constitutes our “microflora” and averages about 3.3 lbs (1.5 kg) per person.
Previously, most of these microbial “passengers” went unidentified, as they were difficult or impossible to grow in laboratories.
But over the past five years, a European research team called MetaHIT has employed advanced DNA analysis to map human intestinal bacteria.
Recently, the MetaHIT team analyzed the genes of intestinal bacteria from 292 Danes, with surprising, disturbing results (Le Chatelier E et al. 2013):
- About one in four people had 25 percent less gut bacteria and a less diverse array of species.
- People with a sparser, less-diverse microflora were more likely to be obese, compared with their peers.
- Bacteria-poor people who’d already developed obesity continued to gain weight over a period of nine years
- The microflora of bacteria-poor people was dominated by species that cause chronic inflammation in the digestive tract and entire body.
- Blood tests on the bacteria-poor participants revealed a state of chronic inflammation, which is proven to raise the risk of type 2 diabetes and cardiovascular diseases.
Adding insult to injury, obesity (especially excess belly fat or “adiposity”) promotes chronic inflammation.
The scientists were careful to note that they don't know which comes first: low bacteria counts or metabolic disorders.
Low bacteria counts seem much more likely to be a cause of metabolic dysfunction. Regardless, the MetaHIT team say that low bacteria counts form part of a vicious, unhealthful cycle.
They say that their goals are twofold: Identify gut bacteria that produce appetite-inhibiting substances, and learn how to safely alter gut bacteria profiles to help prevent obesity, cardiovascular disease, and type 2 diabetes.
Plant antioxidants interact with gut microflora, beneficially
Foods rich high in “antioxidant” polyphenol compounds improve markers for cardiovascular health.
These include vascular health, platelet function, blood pressure, blood fat profiles, oxidative stress (from poorly controlled free radicals), inflammation, and artery lining function.
Now, a novel lab experiment suggests that polyphenols from plant foods can modify the composition of our gut ecosystems.
A team from Unilever used experimental colonies resembling human microflora to test two things (Kemperman A et al. 2013):
- The effects of polyphenols on the human gut ecosystem.
- To identify the metabolites (byproducts of metabolism) produced by its diverse microbes.
Most dietary polyphenols reach the lower intestinal tract, and interact with microbes in the small and large intestine.
Although very few dietary polyphenols make it into our blood or other tissues, they exert beneficial effects indirectly, via "nutrigenomic" influences on our genes.
And those beneficial effects on our genes – antioxidant, anti-inflammatory, anti-cancer, and more – occur in response to the minuscule amounts of intact polyphenols that make into our blood and tissues.
The Unilever team found that some bacteria transform polyphenols into metabolites that enhance absorption of the parent polyphenol compounds in to the blood (Kemperman A et al. 2013).
Further, they found that polyphenols alter the composition of intestinal bacteria:
- Black tea polyphenols stimulated growth of Klebsiella, enterococci, and Akkermansia species while reducing the numbers of bifidobacteria, B. coccoides, Anaeroglobus, and Victivallis species.
- Red wine polyphenols promoted growth of Klebsiella, Alistipes, Cloacibacillus, Victivallis and Akkermansia, while reducing the numbers of bifidobacteria, B. coccoides, Anaeroglobus, Subdoligranulum and Bacteroides.
As they wrote, “The study shows that these complex polyphenols in the context of a model system can modulate select members of the human gut microbiota.” (Kemperman A et al. 2013)
While more study is needed, it seems likely that these changes to our microflora will prove generally desirable, given the broadly beneficial effects of dietary polyphenols
Low-fat diet raised bacteria counts in overweight people
The same issue of Nature that presented the MetaHIT study on bacteria counts and metabolic health included a related study that yielded hopeful signs.
A French research team reported that a low-fat diet may help improve the microfloral community in overweight individuals with fewer, less diverse intestinal bacteria (Cotillard A et al. 2013).
After eating a low-fat diet for just six weeks, intestinal bacteria in these overweight, bacteria-poor people grew both in numbers and diversity.
This outcome indicates that bacteria-poor people can enhance their gut bacteria simply by changing their dietary habits.
Of course, we cannot change our DNA.
But thanks to the new gut microbe research, we can start exploring and exploiting interactions between genetics, diet, and gut bacteria.
- Cotillard A et al. Dietary intervention impact on gut microbial gene richness. Nature 500, 541–546 (29 August 2013) doi:10.1038/nature12506. Received 10 April 2012 Accepted 26 July 2013 Published online 28 August 2013
- Kemperman A, Gross G, Mondot S. et al. Impact of polyphenols from black tea and red wine/grape juice on a gut model microbiome. Food Research International. Volume 53, Issue 2, October 2013, Pages 659–669. doi: 10.1016/j.foodres.2013.01.034
- Le Chatelier E et al. Richness of human gut microbiome correlates with metabolic markers. Nature 500, 541–546 (29 August 2013) doi:10.1038/nature12506. Received 10 April 2012 Accepted 26 July 2013 Published online 28 August 2013
- van Dorsten FA, Peters S, Gross G, Gomez-Roldan V, Klinkenberg M, de Vos RC, Vaughan EE, van Duynhoven JP, Possemiers S, van de Wiele T, Jacobs DM. Gut microbial metabolism of polyphenols from black tea and red wine/grape juice is source-specific and colon-region dependent. J Agric Food Chem. 2012 Nov 14;60(45):11331-42. doi: 10.1021/jf303165w. Epub 2012 Nov 1.
- van Dorsten FA, Grün CH, van Velzen EJ, Jacobs DM, Draijer R, van Duynhoven JP. The metabolic fate of red wine and grape juice polyphenols in humans assessed by metabolomics. Mol Nutr Food Res. 2010 Jul;54(7):897-908. doi: 10.1002/mnfr.200900212.
- van Duynhoven J, Vaughan EE, Jacobs DM, Kemperman RA, van Velzen EJ, Gross G, Roger LC, Possemiers S, Smilde AK, Doré J, Westerhuis JA, Van de Wiele T. Metabolic fate of polyphenols in the human superorganism. Proc Natl Acad Sci U S A. 2011 Mar 15;108 Suppl 1:4531-8. doi: 10.1073/pnas.1000098107. Epub 2010 Jun 25.