You do your best to live right — you eat all the right foods, shy away from alcohol, tobacco and drugs and are fastidious about your hygiene. Still, that temple that is your body is a breeding ground for bacteria.

There have been estimates that there are 10 times as many microbes associated with the human body than there are human cells in it — as many as 100 trillion microbes, extending from your mouth down through your gastrointestinal tract and into the vaginal tract of women. They also reside on your skin. More than 400 species of bacteria call your body home, an ecology of microbes known as the gut flora.

You need most of these microbes — the good bacteria — to live a healthy life, since they're involved in the development of the immune system, prevention of infection from pathogenic or opportunistic microbes — the bad bacteria — and the maintenance of your large and small intestines.

Sometimes the chemistry gets out of whack and the bad bacteria flourish. Maybe you're hit with a case of diarrhea, or you've developed irritable bowel syndrome. Maybe that hamburger you had for lunch was a veritable incubator for E.coli bacteria, and you get very sick.

Maintaining a healthy gut flora is an important part of maintaining your health and — the theory goes — probiotics can play a large role in keeping your gut flora healthy.

What are probiotics?

The Food and Agriculture Organization of the United Nations (FAO) has defined probiotics as "live microorganisms administered in adequate amounts which confer a beneficial health effect on the host." Good bacteria.

They are dietary supplements that are supposed to help boost levels of the good bacteria and keep your gut flora healthy, by keeping the bad bacteria from gaining the upper hand.

They've been understood for half a century, but it's only been in the last decade that they've generated much interest in North America. However, a recent survey found that just under half of Americans say they've never heard of the term.

How do they work?

The theory is, high doses of these good bacteria get into your intestinal tract and boost your immune system. But the problem is, it's a hazardous trip down your esophagus, into your stomach and through your intestines.

Anything that goes down is subject to breakdown by gastric juices, containing digestive enzymes and hydrochloric acid. Survival — even for bacteria — is not guaranteed.

Adding the bacteria to food — especially dairy products — buffers stomach acid and increases the chance that the bacteria will survive into the intestine and help restore balance to the gut flora.

What they won't do is replace the body's natural flora when they have been killed off. There is evidence that probiotics can form temporary colonies that can help — but those colonies will disappear within days if you stop taking the supplements.

What are the benefits of probiotics?

There have been claims that probiotics can help with anything from diarrhea to hypertension and cancer, but for most of those claims, the evidence is not very clear.

However, it's been established that Lactobacillus — one of the good bacteria — is safe and effective as a treatment for children with acute infectious diarrhea.

There have been claims that probiotics can be an effective way to treat irritable bowel syndrome, with studies suggesting relief in some symptoms, mainly from diarrhea, abdominal pain and bloating.

It has also been shown that probiotics can make it easier for lactose-intolerant people to consume fermented dairy products like yogurt with fewer symptoms than the same amount of unfermented milk. Yogurt was found to aid digestion of lactose because the lactic acid bacteria used to make yogurt produce lactase and digest the lactose before it reaches the colon.

A recent study suggested that probiotics may have positive implications for colorectal cancer. The study found that "symbiotic intervention" led to significant changes in fecal flora which resulted in a reduction in the destruction of colonic cells. The study concluded that "several colorectal cancer biomarkers can be altered favorably by symbiotic intervention."

Are there side effects?

As with any medicine, there can be. The most common are diarrhea, bloating, constipation and gas. Cutting the dose may curb those side effects.

How can I tell if a product contains probiotic?

Check the label. Yogurt is one of the most common ways of delivering probiotics. Another is through capsules containing "good bacteria."

The "good bacteria" that you are consuming are live microorganisms and do have a limited shelf life. The good bacteria may already be dying off when you buy the product. With yogurt, scientists say there should be one million to one billion active cultures per gram to be considered probiotic.