We don't normally like to think of it but humans have a symbiotic relationship with many tiny organisms. 'Symbiosis' means two or more species interacting, sometimes very closely, and gaining mutual benefit from the relationship. 'Closely', in this case, actually means: inside our bodies.

The intestinal flora that live inside our colon is a good example. There are over 700 different species of bacteria inside the human gut, most of which are beneficial. They are essential to healthy digestion and even help produce some vitamins, along with aiding the immune system. They also lower the pH of the intestine slightly, which inhibits the growth of some pathogens (harmful organisms) like salmonella.

That balance of good bacteria to potentially harmful bacteria can get out of whack, though. Antibiotics, stress, and other factors can lower the amount and ratio of helpful digestive bacteria. When that happens, probiotics - supplements or food additives that contain some of those species - can be a useful health aid.

Dannon Activia, for example, has become a well-known brand/type of yogurt that goes beyond the usual benefits of that food. It contains additional probiotics that have a clinically proven, and real-world tested benefit. Less intestinal gas and cramping, firmer stools, and other benefits have been well documented. Another probiotic, the now-common Lactobacillus acidophilus 'additive' (an ingredient in many probiotics) has long been known to aid in treating constipation.

In some instances you may see listed among the ingredients of supplements or foods the word 'prebiotics'. These additives are not bacterial species themselves (i.e. they're not technically probiotics) but contain 'food' for the probiotic species or those that naturally live in the colon.

Prebiotics, like most supplements or food additives, cover a wide range of type and quality and may be beneficial or may be nothing but hype. The only way to know is to research an individual product. The same may be said of probiotics, but here the research is a little more substantial. Major manufacturers with respected reputations have more well-known and trustworthy products.

The two most common prebiotics on the market are whey and FOS (fructo-oligosaccharides).

Whey is the liquid 'waste' left behind when cheese curds are separated off during cheesemaking. However, what is waste in one circumstance can be a very useful product in another. Whey has been consumed for centuries by cultures around the world and has known health benefits. That's not surprising, since it's chiefly water, potassium, calcium, phosphorus, lactose, fat, and water-soluble vitamins. Naturally, those with lactose intolerance should avoid this type of prebiotic.

FOS is a type of sugar that humans don't possess the enzyme needed to break down. Fortunately, bifidobacteria in the colon do have that ability. One of those 700 naturally occurring species mentioned, this tiny organism aids digestion and so 'feeding' it can be beneficial, in the right amount. It's found naturally in tomatoes, bananas, honey, barley, and other foods. Their growth can also be encouraged by the intake of fiber.

While no miracle cure, probiotics can be useful in the treatment of diarrhea, vaginal yeast infections, and IBS (irritable bowel syndrome). As with any significant change to diet or when attempting to home-treat illness, it's always wise to consult with your physician.