Body Ecology

Yosemite Valley has a different ecology today than it had 100 years ago. As the human population increased the mountain lion population decreased—some mountain lions traveled to friendlier territory, most were executed. With the loss of these top predators, the mule deer population increased. One the deer’s favorite foods is oak seedlings. The deer overgrazed the oak seedlings as a consequence fewer oaks grew. Pines opportunistically moved in to take their place. Eventually, what had been a climax oak ecosystem became an emerging pine ecosystem. With the loss of the oaks came a loss in Yosemite Valley’s biodiversity.

The human body has it’s own ecology too that can be knocked off balance by disruptive forces.

Our ecology consists of a human and several hundred species of bacteria. These commensal bacteria live happily together and with us—at least when things work right. When they don’t, we experience what’s called dysbiosis.

Many of you are no doubt familiar with this term as it pertains to diseases of the gut. Although the vast majority of commensal bacteria live in the gut, they also live on our skin, mouth, nose, vagina, and just about every other place that comes in contact with the “outside.” I know your gut seems like it’s very inside, but its lining is very much a barrier as important as your skin in controlling what gets into you blood stream and internal organs.

The complexity of this ecosystem has only recently received the scientific attention it deserves. A Human Microbiome Project was recently launched to focus research on this complex ecology and how it affects health and illness. Of course, we already know a good deal about how our bacterial ecosystem can be disrupted. One of the most common is the use of antibiotics. Ironically, routine use of antibiotics might make you more vulnerable to attack by pathogens: your bacterial ecosystem is a key part of your immune response; if it’s weakened, so is your immunity.

Newer research is revealing the role that commensal bacteria play in detoxification, in particular in neutralizing carcinogens. It is not yet clear whether these detoxifying bacteria can be overwhelmed by a toxic load, but it makes sense to me that they would. So in our increasingly toxic world, our capacity to remove toxins becomes yet another way in which our body ecology is compromised.

A recent study by Ruth Ley and her colleagues at the Human Microbiome Project—published in Science magazine—asked how mammals evolved with such a complex ecology. The earliest mammals were carnivores. We mammals have now evolved so that 80% of us are herbivores, like mule deer. It’s no coincidence that although mammals emerged 160 million years ago, the real emergence of mammals didn’t happen until 2 million years ago with the spread of great savannahs—that is, grass lands, those great herbivore diners.

Some mammals continued to evolve as carnivores. Most evolved into herbivores. Still others evolved into omnivores—like humans. You can tell the difference not just by what each type of mammal eats but by the kind of bacterial ecology they have in the gut. In fact, the Ley study found that each mammal species and its bacterial gut ecology evolved together. The relationship between a mammal and its gut ecology is so close that when the bacteria from one mammal species is introduced into another mammal that has been raised in a sterile environment so it doesn’t have any indigenous bacteria, the foreign bacteria adapt to the new gut. It’s as if you’d taken a room full of salsa dancers to a ballroom, struck up a waltz, and soon witnessed couples gliding across the floor.

One of the study’s 16 human subjects was a vegetarian. That person’s gut ecology was indistinguishable from 15 meat eaters. It brought home to me that humans evolved to take advantage of a wide variety of food conditions, which we’ve further adapted culturally using agriculture and cooking. The bacteria that travel with us have evolved as well to take advantage of that variety. In fact they depend on that variety.

We need to support our body ecology. Avoiding antibiotics is one way. Avoiding toxic exposures is another. But the basic support is from an omnivorous diet. It’s what we and our bacterial companions are built for.