One hundred trillion. Nope, it's not the national debt. That mega-number is the population of microbes living it up in your digestive system. Most of you think about this inner zoo only when it pumps out too much gas at an embarrassing moment or sends you running to the bathroom with diarrhea. But these days there's a lot of important research going on about this inner world, and it's revealing that these bacteria are essential for your good health.

As Dr. Mike points out in his new book, "This is YOUR Do-Over," changing your inner zoo or microbiome so it has a healthy mix of these little critters is a key step to reclaiming or maintaining your health.

Then you can make sure potentially harmful bacteria in the mix don't trigger problems such as autoimmune diseases, persistent infections (like C. diff.) and even heart woes.

In fact, if you keep the inhabitants of your microbiome plentiful and diverse, they can keep your arteries young, strengthen your immune system and help you slim down and live longer.

So time for a gut check! Here's how to start your gut-biome do-over today.

Moving your body regularly - walking, riding your bike, hitting the gym - helps support a more diverse mix of gut bacteria.

In a recent study of 40 pro rugby stars, researchers from Ireland's University College Cork found that the players' intestinal biome contained a wider variety of bacteria than that of fairly sedentary men the same age and size.

The rugby players also had Akkermansiaceae, a bacterium that's been linked to lower risk for obesity. That's another reason for a minimum 30-minute daily walk, seven days a week, shooting for your target of 10,000 steps every day.

Yogurt, kefir (a fermented milk drink) and fermented foods like sauerkraut, kimchi and tempeh (a soy-based meat alternative) are good sources of beneficial bacteria.

Many yogurts contain helpful probiotics. Look for the words "spore forms" or "live, active cultures" on the label. (Spores are activated in your gut rather than killed by your stomach acid.)

Probiotic-rich foods often deliver Lactobacillus gasseri, shown in two recent studies to discourage weight gain and help with weight loss.

There's also evidence that a daily serving of probiotic-enriched yogurt can cut your risk for antibiotic-related diarrhea by two-thirds. This condition is triggered when the meds wipe out both the bad and good bugs in your digestive system and is a problem for 39 percent of people who take antibiotics.

Two important beneficial bacteria, bifidobacteria and lactobacilli, love munching on a family of plant fibers called fructans, especially a type called inulin.

It's found in abundance in bananas, onions, garlic, leeks, asparagus, artichokes, soybeans and 100 percent whole-wheat foods.

Gut bacteria release substances when they break down red or processed meats. The substances end up in your bloodstream, causing inflammation throughout your body, which increases your risk for clogged arteries, memory dysfunction and cancer.

Egg yolks elicit the same response, changing your inner zoo in favor of harmful bacteria. Red meat also may prompt bacteria to produce substances that interfere with the constant, healthy renewal of the inner lining of the intestines, increasing your risk for colon cancer.

Overeating encourages the growth of a gut-bug strain called Firmicutes that could accelerate weight gain, say researchers from Washington University in St. Louis.

Turns out Firmicutes break down foods with extreme efficiency, making more calories available to your body for use - and weight gain!

That means overeating could be a double whammy: You're eating more calories and absorbing even more.

In one study, a 20 percent increase in the number of Firmicutes in the human gut made an extra 150 calories a day available for absorption.

So keep your calorie intake in a healthy lower range to encourage growth of bacteria that make fewer calories available.

Mehmet Oz, M.D. is host of "The Dr. Oz Show," and Mike Roizen, M.D. is Chief Wellness Officer and Chair of Wellness Institute at Cleveland Clinic.