For many years, intestinal microorganisms were viewed largely as organisms that happened to live inside us. We now understand that the relationship is far more dynamic. These microorganisms interact continuously with their environment, and one of the most important components of that environment is food.<\/p>\n\n\n\n
The microbiome possesses biochemical capabilities that humans do not. Microbial genomes collectively contain an enormous number of genes capable of producing enzymes different from those encoded by the human genome. These enzymes allow microorganisms to interact with dietary compounds that our own digestive enzymes may be unable to process completely. [1,2]<\/p>\n\n\n\n
This greatly expands what can happen to food after we eat it.<\/p>\n\n\n\n
Dietary fiber provides a familiar example. Humans lack many of the enzymes required to break down complex plant carbohydrates. Consequently, portions of these carbohydrates can pass through the small intestine without being digested. But reaching the colon does not necessarily mean that their biological journey is over. There they encounter microorganisms equipped with enzymes capable of acting upon them.<\/p>\n\n\n\n
The same general principle applies to many other components of plant foods. Some portions of resistant starches, complex carbohydrates, polyphenols, and other compounds may reach the colon, where microbial processing can continue what human digestion could not accomplish alone. [4,5]<\/p>\n\n\n\n
The colon, therefore, is not simply the end of digestion. It is also home to an enormous biochemical community.<\/p>\n\n\n\n
A Community Working Together<\/h3>\n\n\n\n
It would also be misleading to imagine each microorganism working independently.<\/p>\n\n\n\n
The microbiome behaves more like an ecosystem.<\/p>\n\n\n\n
Different microorganisms have different biochemical capabilities. One organism may begin breaking apart a complex dietary component. Another organism may use what the first organism releases. A third may depend upon products generated by the second. These relationships create interconnected microbial networks in which the activities of one organism can influence the activities of others. [4,5]<\/p>\n\n\n\n
This cooperation is particularly important when complex foods enter the colon. Plant material may contain chemical structures that cannot be handled by a single microbial species. Instead, different members of the community can participate in different stages of processing.<\/p>\n\n\n\n
In this sense, the microbiome adds another layer of biological capability to human digestion.<\/p>\n\n\n\n
We eat the food, but we are not the only organisms processing it.<\/p>\n\n\n\n
Food Shapes the Microbiome<\/h3>\n\n\n\n
The relationship between food and microorganisms also works in both directions.<\/p>\n\n\n\n
The microbiome acts upon food, but food helps shape the microbiome.<\/p>\n\n\n\n
Like organisms in any ecosystem, intestinal microorganisms require resources. Different organisms are adapted to use different substrates. The foods that reach the colon therefore help determine which resources are available to the microbial community.<\/p>\n\n\n\n
A dietary pattern containing a variety of plant fibers and resistant carbohydrates creates one type of intestinal environment. A dietary pattern in which relatively little fermentable plant material reaches the colon creates another. Microorganisms capable of using the available resources may gain an ecological advantage, while organisms dependent upon other substrates may become less active or less abundant.<\/p>\n\n\n\n
Human studies have demonstrated that dietary patterns are associated with differences in microbial communities and that substantial dietary changes can alter microbial activity surprisingly quickly. [6\u20138] This does not mean that eating one particular food permanently changes the microbiome. The intestinal ecosystem is influenced by many factors and is continually adapting.<\/p>\n\n\n\n
Diet, however, is one of the environmental factors we repeatedly introduce into that ecosystem.<\/p>\n\n\n\n
Every meal changes, at least temporarily, what is available.<\/p>\n\n\n\n
A Living and Individual Ecosystem<\/h3>\n\n\n\n
There is no single universal human microbiome.<\/p>\n\n\n\n
Microbial communities vary considerably from one person to another. They are influenced by diet, age, medications, antibiotic exposure, intestinal transit, environment, geography, illness, and interactions among the microorganisms themselves. Even within the same person, the microbiome can change over time. [3,9,10]<\/p>\n\n\n\n
This variability introduces an important dimension to Food as Information.<\/p>\n\n\n\n
Two people can eat the same bowl of oatmeal, the same beans, or the same berries. Chemically, the food may be essentially identical. But once that food enters the gastrointestinal tract, it encounters two different biological ecosystems.<\/p>\n\n\n\n
What happens next therefore does not depend solely upon what was in the food. It also depends upon who receives it<\/strong>.<\/p>\n\n\n\n This is one reason nutrition cannot always be understood simply by analyzing the chemical composition of a meal. The biological potential contained within food encounters a living, changing microbial community before much of its story has been completed.<\/p>\n\n\n\n Thinking about the microbiome changes the way we think about eating. When we eat, we are not supplying nutrients only to ourselves. We are also introducing resources into an ecosystem of microorganisms living within us.<\/p>\n\n\n\n Some components of food will be digested and absorbed before they ever reach that ecosystem. Others will travel farther. When they reach the colon, they may become available to microorganisms possessing biochemical abilities very different from our own.<\/p>\n\n\n\n Human digestion and microbial processing therefore form a biological partnership. Our digestive system begins the work. The microbiome can continue it. And in doing so, microorganisms can begin to unlock possibilities within food that human digestion alone could not access.<\/p>\n\n\n That simple observation captures the central message of this chapter.<\/p>\n\n\n\n The microbiome is not simply something we carry around inside us. It is an active biological community continually interacting with the foods we eat.<\/p>\n\n\n\n And those interactions matter because microorganisms can change food. They can take compounds arriving from our diet and transform them into something different.<\/p>\n\n\n\n What they create is the subject of the next chapter.<\/p>\n\n\n\nWe Are Feeding an Ecosystem<\/h3>\n\n\n\n
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