Many people think of their digestive systems as a series of tubes through which food is mechanically crushed and extruded. It’s not as simple as that. Your gut’s health determines which nutrients are absorbed and which toxins, allergens and microbes are repelled. As a result, it is directly linked to the health of your entire body.

Intestinal health could be defined as the optimal digestion, absorption and assimilation of food. But that is a big job that depends on many other factors.

First, the bugs in your gut function like a rainforest — a diverse and interdependent ecosystem. The 3 pounds of bacteria there include some 500 different species that act as a chemical factory — helping you digest your food, produce vitamins, regulate hormones, excrete toxins and produce healing compounds that keep your gut healthy.

But for you to be healthy, these bacteria must be in balance. Too many of the wrong bugs, like parasites, yeasts and bad bacteria — or not enough of the good bugs, like lactobacillus or bifidobacteria— can seriously damage your health.

Second, the gut is delicate. Your entire immune system and the rest of your body are protected from the toxic environment in the gut by only a one-cell-thick layer — the epithelium — that covers a surface area the size of a tennis court! If that barrier is damaged, you will get sick and your immune system will become overactive, producing inflammation throughout the body.

And then there’s your second brain. That’s right, your second brain. Your gut literally contains its own nervous system. In fact, the ”brain” in your gut contains more neurotransmitters than the brain in your head.

The intestinal nervous system is wired back to your brain, and messages travel between the two. When those messages are altered for any reason in any direction — from the brain to the gut or the gut to the brain — your health will suffer.

But wait, there’s more: Your gut also has to dispose of all the toxins created as a byproduct of your metabolism. If things get backed up, your entire body can become overrun with toxins.

Finally, in the midst of all of this, your gut must break down all the food you eat, separate all the vitamins and minerals, and shuttle everything across the epithelium into your bloodstream for you to stay healthy.

Enemies of a Healthy Gut

With such a delicate balance and so many ways for things to go wrong, it’s no wonder that so many of us are sick. Even in a perfect world, our gut has a hard time keeping things balanced. In the challenging circumstances of real life, there’s seemingly no end  to the things that knock our digestive systems off balance. They include:

• • A standard American diet (SAD) that is low in fiber, rich in sugar, low in nutrients, and high in additives and chemicals, changing the ecosystem of our guts
  • Overuse of medications, such as anti-inflammatories, antibiotics, acid-blocking drugs (see “The Dangers of Acid-Blocking Drugs,” below) and steroids, that disrupt the gut’s ability to stay in balance and do its job
  • Chronic low-grade infections or gut imbalances with bacterial or yeast overgrowth, parasites, or even more serious gut infections
  • Exposure to toxins, such as mercury and mold, that damage normal gut function
  • Lack of adequate digestive enzyme function, which can be caused by acid-blocking medications or zinc deficiency
  • Chronic stress, which can alter the gut’s nervous system, causing a leaky gut and changing the normal bacteria in the gut