Once upon a time, our human ancestors ate mostly plants. Microbes evolved in tandem, metabolizing fibers and forging a genome to coexist nicely with byproducts such as short-chain fatty acids.
Today our microbial communities look quite different.
They struggle mightily to adapt to high fat and sugar diets processed with a litany of additives. Overuse of antibiotics washes them out completely. The barrage continues with other trappings of modern life.
It’s important to note that while our microbes can change quickly, the human genome, in its inimitable Darwinian fashion, needs more time, even generations to adapt. This lag may contribute to the rise in purely modern health problems. Diabetes, heart disease, cancers and autoimmune disorders may reflect the damage.
One stark example of this: microbes which are excellent “energy harvesters” hence historically crucial in a famine may drive obesity when food is (over)abundant as it is today in many countries.
Erica D. Sonnenburg and Justin L. Sonnenburg recently took a broad look at the subject in The ancestral and industrialized gut microbiota and implications for human health which appeared in Nature Reviews Microbiology
Ancestral vs. industrialized
Key changes in microbiota according to the authors:
- A trio of bacterial taxa that were prevalent in traditional microbiota is rare today in industrialized regions. Prevotellaceae, Spirochaetaceae and Succinivibrionaceae, once quite common taxa are now almost absent. Dietary changes are one major cause of the absence. Food fibers have been replaced by large helpings of protein, fat and sugar as well as non-food chemicals, including preservatives, pesticides, additives and emulsifiers. The switch has had a big impact on host–microbiota interactions. Species which degrade fibers have faltered.
- Another change is the absence or low presence of mucus-degrading enzymes and mucus-consuming species which result in maladaptive response such as inflammation.
- Antibiotic use results in drastic, acute changes in the microbiota, and the effects can be persistent. Bacterial species that harbor antibiotic-resistant genes have emerged.
Yet some readers point out that modern man can expect to live much longer than our ancestors. These numbers are skewed because infant mortality was much higher back then. One often-studied community which mimics the ancients is the Hadza hunter-gatherers in Tanzania. After adulthood, they have a life expectancy of 76 years with rare occurrence of heart attacks and strokes, a common cause of death in older Americans.
These diseases of civilization require a new approach
The authors set out several strategies to improve health by targeting the gut microbiota:
- Population-wide interventions to include diet changes and reduced antibiotic use.
- Support for healthy gut microbes starting in early life. This could include plant-based diets or even seeding with beneficial microbes which have all but vanished.
“Rapid modernization, including medical practices and dietary changes, is causing progressive deterioration of the microbiota, and we hypothesize that this may contribute to various diseases prevalent in industrialized societies.”