The importance of fiber in our diets has been understood for many years. However, recent studies in many countries have provided clear evidence that, at least as far as our gut bacteria are concerned, we are what we eat. Japanese that eat sea weed have gut bacteria that digest sea weed. Africans that eat root vegetables and tubers have gut bacteria that digest those foods. People in the western world that eat less fiber and more fat and sugar have less diverse communities of gut bacteria and in the worst cases those bacteria are forced out of their role of supporting their host and left to feed on the intestinal lining in order to survive. It is increasingly clear that this survival response is the underlying cause of many of the gastric and auto-immune disease associated with our Western culture.
According to data developed by the National Institute of Health’s Human Microbiome Project and the American Gut Project based at the University of Colorado, there are only about a dozen bacterial phyla (of families) that make up most Microbiomes. The major families are Firmicutes and Bacteroidetes followed by Proteobacteria, Actinobacteria and Tenericutes. Firmicutes include species like Clostridium and Lactobacillus that produce the short-chain fatty acids that are key inputs to our immune systems. Bacteroidetes include species like Bacteroides and Prevotella that break down big sugars (polysaccharides). While the other phyla comprise a much smaller percentage of our gut bacteria they are important because they appear to be the specialists that do the initial breaking down of particular foods. The loss of even a few of these specialized bacteria can significantly change our ability to digest particular fruits, grains or vegetables. This combination of “specialists” and “generalists” is what allows our microbiomes to deal with varied diets and challenges. Research by Pål Trosvik and Eric Jacques de Muinck highlights this distinction between “foundation” and “keystone” gut bacteria.
What this means is that, much like an athletic team, our gut bacteria work together to live and carry out their digestive and disease fighting role. When fiber arrives in our gut, those bacteria with the special ability to break down that particular fiber attack first. As they break down the primary fiber, the byproducts produced become raw material for other members of the colony. Ultimately, the entire community is nourished and in turn produces the short chain fatty acids that are the building blocks for our intestinal lining, our immune system and many of the compounds and enzymes that impact our physical and mental health.
Over time, what we eat determines the make-up of our Micro Biome. If we stop eating certain fibers then the bacteria specialized in dealing with those fibers will diminish or disappear. If we resume eating that fiber then we may suffer some discomfort until that bacteria re-establishes itself in our microbiome. When we understand this concept of “keystone” bacteria it is clear that it is almost impossible to support a healthy microbiome with a “hit or miss” strategy of including fiber in our diet. We need to monitor and manage our fiber intake as closely and as carefully as we do our calories.
The American Gut Project has shown that while age, exercise and diet all affect the composition and mix of the gut bacteria that comprise our Micro Biome, the indiscriminate use of broad spectrum antibiotics can undo all of our good work almost overnight This is particularly true when it comes to the less numerous “keystone” varieties where the loss of a few bacteria can significantly affect our ability to deal with different foods and hostile bacteria. As a result, antibiotics have a disproportionate impact on the the critical functions of our microbiomes. There are times when antibiotics are important to restoring our health but it is clear that we should follow any course of antibiotics with an active campaign to both nourish and re-populate our gut bacteria.