Prebiotics and probiotics are both aimed at maintaining healthy colonies of beneficial bacteria in our gastrointestinal (GI) tracts. Our bodies are veritable smorgasbords for a vast range of bacteria, helminths, protozoa, viruses and yeasts. But it is not all bad. Our relationship with many of the bacteria that colonize the GI tract of our digestive system is a type of symbiosis called mutualism. This means that both sides benefit and prosper from the interaction. These are the "good bacteria" we hear about a lot these days, particularly in advertisements for prebiotic and probiotic products; they are often referred to as intestinal flora.
Although the ultimate goal is the same, the approach taken by prebiotics and probiotics is completely different, but not exclusive. In many situations they will be most effective used in conjunction with each other.
Prebiotics might be thought of as dietary supplements for bacteria. They contain carbohydrates that these bacteria need but our bodies generally do not. Such substances may be limited in our normal diets, although they are found in high fiber foods like bananas, onions, tomatoes and whole wheat. When they are in short supply it limits the growth rate and functionality of bacterial colonies, reducing the benefits they can supply our bodies. By supplying these resources, prebiotic products remove those limitations, so a bacterial colony can flourish and function to its full capabilities.
Probiotic products, on the other hand, supply the bacteria. Instead of feeding the bacterial colonies already present in the GI tract, they bring in more good bacteria to boost the numbers. These products are often yoghurts for this reason, as yoghurts are very good transport mediums for bacteria.
In exchange for what to them is a nice environment to live in, usually with ample food, these beneficial bacteria perform two main services: digestive and protective. To get their own energy and nutrients they break up organic molecules into smaller ones. Often our bodies do not produce enzymes or digestive juices capable of doing this, especially for some of the plant organic molecules in our food. But we can digest the derivatives left after bacteriological action or those might already be small enough to be absorbed through our intestinal walls. Plant materials can be particularly tough on animal digestive systems, which is why ruminant herbivores such as cows are completely dependent on the bacteria providing this service in their multiple stomachs and intestines.
The bacteria provide protection for our GI tracts simply by being there and through self-protective actions. Invading pathogens attempting to grow where they are already established will have great difficulty. The colonies do not want competition for growing surfaces or resources and many produce exotoxins that inhibit bacterial growth other than their own. Bacteria have prokaryotic cells while our cells are eukaryotic, so these exotoxins are not normally harmful to us. Other pathogens, such as viruses and yeasts, may not be able to reach our cells through the layered bacterial cells of a colony. Thus the healthy colony provides physical protection in the form of a barrier. Recent research indicates that a healthy community of intestinal flora benefits allergy sufferers and may reduce the likelihood of children developing asthma.
This does not mean that prebiotics and probiotics should be taken at any and all times. A fit and healthy person on a balanced diet, with a lifestyle that excludes excesses, will be fine without these products. But they may be even better using them in a limited fashion, it would certainly be worthwhile experimenting to find out and quite simple to do so. Take a probiotic first to increase the number and possibly types of beneficial bacteria in your GI tract. Follow it with a prebiotic that will feed the bacteria from the probiotic and those that were already present. If it seems to benefit you, for example with increased energy or more regular and comfortable toilet visits, then you may choose to continue taking these products. The frequency would be dependent on the specific individual, but once per 7 to 10 days would probably be sufficient for the prebiotics and once a month for the probiotics.
For people with lifestyles harder on the body, those who smoke, drink alcohol and/or use drugs, both may be very helpful for their systems. Alcohol can be used to sterilize wounds because it kills bacteria. While our intestinal flora can survive and recuperate after a drink or two, heavier drinking is likely to kill many, part of the reason our digestive systems feel poorly after an excessive night out. A probiotic as part of a morning after cure, to replenish our beneficial bacteria, would be a very good idea. A prebiotic a couple of hours later once they are established would boost their growth. For most serious drinkers such a regimen would probably be common enough to be sufficient; for the person who binge drinks only on rare occasions, additional intakes may be useful.
For those who take toxic substances into their bodies via alternative routes to the digestive system, such as smokers and intravenous drug users, there is no direct attack or inhibition of their intestinal flora. However general body function is usually impaired because of the effects of these substances, and this will include digestive system function. Prebiotics and probiotics are likely to prove helpful, but the appropriate regimen would be specific to the individual, so no such advise can be offered here. Consultation with a medical practitioner is advised in these circumstances.
With illness some care needs to be taken. While prebiotics are targeted towards beneficial bacteria they may also provide a boost to an infectious, pathogenic bacteria. Some beneficial bacteria can also be opportunistic, expanding beyond desired bounds if our immune systems are weakened during illness. If a person becomes sick it would be safest to stop taking prebiotics and probiotics until you have consulted with your physician. In most cases probiotics will be okay to continue with, especially so if you are prescribed a course of general antibiotics.
Antibiotics, as the name implies, kill or inhibit the growth of bacteria. Some are targeted, affecting only a certain class of bacteria, while others are broad spectrum, impacting a large range of bacterial types. Some of the side effects of broad spectrum antibiotics are due to their killing our beneficial bacteria. If, after consultation with your doctor, you take probiotics during the period you are taking the antibiotics you will be able to partially maintain the beneficial bacteria while the pathogenic ones are being eradicated. Whether you do or not, taking probiotics after the course has been completed is a good start to restoring a healthy community of intestinal flora. Once a bacterial infection has been treated, prebiotics might be used to feed that community back up to strength.
Sources:
Kopp, M. & Salfeld, P. (2009) Probiotics and prevention of allergic disease. Current Opinion in Clinical Nutrition and Metabolic Care 12(3): p298-303.
Looijer-van Langen, M. & Dieleman, L. (2009) Prebiotics in chronic intestinal inflammation. Inflammatory Bowel Diseases 15(3): p454-462.
Minocha, A. (2009) Probiotics for preventive health. Nutrition in Clinical Practice: Official Publication of the American Society for Parenteral and Enteral Nutrition 24(2): p227-241.
Wang, Y. (2009) Prebiotics: Present and future in food science and technology. Food Research International 42(1): p8-12.