Why are so many of us engaged in dietary practices that we know are unhealthy? For many of us, we know the food we eat is literally bad for us- too much fat, too much sugar, too much salt, too many calories. To make matters even worse, even as we polish off one offering or another of the so-called "Western Diet" - we are planning for the inevitable gut wretch that we know is coming our way. It’s not like we haven’t seen it before!
How is it that in the span of minutes, we go from being in confident control of our dietary cravings, taste preferences, and appetite restraint, to zombie eating machines? In some cases, all it takes to flip this switch is the mere sight of food! Well, research shows that our automated, unconscious as well as our pre-planned dietary decisions are mainly controlled by the ultimate beneficiary of any food we eat, our gut microbiome. We do the things we do regarding food because our biome told us to!!
A little background
The biologically active material of chewed up and partially digested food that resides within the large intestine and colon – the gut- is actually the home to trillions of individual living organisms. Using today's modern genetic sequencing and analytical techniques, researchers can identify every bacterium, virus, fungus, and other microorganism that lives in your gut in a matter of a few hours. The list of these microbes and their total numbers are collectively known as the microbiota; something that is uniquely yours-the proportion of the microbial mix of nearly 1000 distinct organisms. In numerical terms, our microbiota outnumber our own "human" cells by a factor of 10! The aggregate of all genetic material wrapped up within our microbiota is call the microbiome. If we compare the length of our “human” DNA with that of our microbiome by laying both side-by-side on a on football field, our gut microbiome would easily span the entire field, while our own DNA would be struggling to get to the 1-yard line! Formally, we may acknowledge the definitional distinctions of microbiota and microbiome, but in the literature, these terms are often combined and simply referred to as our biome.
Why do we allow microbiota to live within our bodies?
Certainly, we have all been conditioned to view bacteria as dangerous and worthy of being sanitized and eradicated. Confirming this view are the advances made in the human condition as a result of our adherence to lessons derived from the germ theory of disease. Therefore, it is remarkable that our microbiota live and thrive within our bodies in the first place! However, co-existing with a mix of “safe” microbes turns out to be a clever and efficient survival strategy. As part of a mutually beneficial host/guest quid pro quo, our body provides a warm and safe place for our microbiota to reside; we provide the food it requires to thrive, as well as a "promise" to hold our immune system in check. In exchange, our microbiota provide access to its vast library of genetic codes within our biome. Why is this important? Outsourcing specialized cellular machinery and biological processes to our biome allows our human genetic blueprint to remain simple, efficient and focused on matters pertaining to propagation of the species. Remarkably, the tasks relegated to our biome are not trivial. Consider the fact that the main source of nutrition in a baby’s very first meal, mother's milk, literally passes untouched by its digestive system; every baby born on earth relies on their biome to produce the enzymes required to convert milk sugars into the chemical components that can be absorbed and utilized by the baby to foster proper cellular function and growth.
Metabolome-Your Own "On Board" Biochemical Factory
In the controlled environment of our gut, bacteria use what we feed it to in part to assure their own survival. In return, the metabolic products from the microbial processing are often the very biochemicals our body has evolved to depend upon. The soup of metabolic biochemicals produced by our gut microbiota is called the metabolome; it is our personal bio-pharmaceutical factory estimated to consist of 500,000 distinct chemical entities. It has been shown that the metabolome contains drug-like compounds that are traditionally associated with brain pharmacology such as neurotransmitters like serotonin and dopamine, hormones and hunger/satisfaction signaling peptides and essential vitamins. An elaborate network of sensory cells and neurons surrounds our digestive system called the enteric nervous system. Often referred to as our "second brain," it has a direct connection to our central nervous system via the Vegas nerve. This provides a direct accounting of the activity within the gut thus defines the manner in which our dietary behaviors-how we feel about food- taste preferences, cravings, satiety, are communicated to our CNS.
Are all Biomes the Same?
Scientists at The American Gut Project and others, have analyzed the microbiome of thousands of volunteers and have shown that the microbial mix within the gut is closely associated with the foods that are consumed. A Western Diet - high in carbohydrates, animal protein and fat, for instance, appeals to and nourishes one set of microbial species, whereas an alternative diet like a plant-based diet caters to an entirely different set of microbes.
Because the microbiota are different for these diets, the microbiome and resulting metabolome are also different. Since a different mix of microbes means a different mix of biochemical produced in the gut, we observe a different mix signals sent to the brain.
What to do? Bio-hack Your Food–Biome Feedback Cycle
For those that are stuck in a never-ending battle with the consequences of the Western Diet, there's great news! It is possible and relatively simple to change our dietary and mental health behaviors by deliberately changing, or bio-hacking the microbial profile within our gut. In the figure below, the predominant populations of microbes in an existing biome accustomed to the Hamburger Diet are well nourished and thriving (see this nice review in American Scientific). In a very self-serving way, the chemicals thus introduced into the metabolome are those that promote dietary behaviors that would assure the continuation of (you guessed it!) the Hamburger Diet. However, microbes multiply and grow at such a rapid pace (the life span is on the order of 20 minutes), it is actually possible to switch out the Hamburger Biome in a relatively short timeframe by eliminating hamburgers and introducing alternative foods-like a Salad Diet. When this is done, the microbes accustomed to Hamburger Diet will begin to divide and grow at a slower pace- lacking the food they need, they are effectively starved out. The result: the Hamburger Biome gets smaller and its ability to control the overall makeup of the metabolome begins to decrease. At the same time, introduction of the plentiful Salad Diet promotes the population growth of the Salad Biome, which then begins to wrest control of the metabolome so that the chemicals signaling dietary behaviors assures the input foods consistent with the Salad Diet. In time, impulses driving dietary choices to assure the Hamburger Diet completely go away. In fact, as unbelievable as it may sound, studies have shown that the changes in the composition of your gut microbiota can be accompanied by changes in your taste preferences; foods you never thought you could live without will fall by the wayside.
As a personal note, I was able to enact such a change in my own diet in a matter of just a few days. I elected to abandon all aspects of the Western Diet and opted for a plant-based diet. Within just 2 or 3 days, I found that my typical cravings- chocolate chip cookies, breads and kettle potato chips- had subsided and were replaced with the acidic taste of fermented foods like homemade sauerkraut and pickles juice and vegetables! Moreover, I noted a change in my perceptions of smell - once upon a time, I longed for the wafting aroma of sizzling meat on the barbecue, but after a very short time, not so much! Even though I have a life-long reputation of having a sweet tooth, and I still like the cookies, I feel that I have less interest in eating them and perhaps most important, I have more power to resist putting my hand into the cookie jar in the first place.
Knowledge is Power
I mention this not to advocate for a plant-based diet (which I actually do!), but only to suggest that despite the sophistication of our biome, we can bio-hack it in a deliberate way to assure that it and generates a metabolome with a blend of signaling chemicals that direct us to make unconscious and executive dietary choices that conform to favorable human health and longevity. We should anticipate that the dying embers of an old biome will test our determination and discipline as we make the necessary changes to replace it, but in a very short time, we will gain the upper hand and the ultimate power to ditch your old biome for a new one that "commands" you to eat right.
Got Biome? Absolutely!
