Probiotics are live bacteria (e.g., lactobacilli) commonly found in yogurt and fermented foods such as sauerkraut and kimchi. They may also be found in certain probiotic-fortified foods such as breakfast cereals, energy bars and beverages. Prebiotics are certain nondigestible substances (usually carbohydrates, such as fructo-oliogosaccharides) in foods that are used as fuel by beneficial bacteria already in the body. Sources of prebiotics include asparagus, bananas, garlic, onions, soybeans and breast milk.

Probiotics are beneficial bacteria that can suppress the growth of potentially harmful bacteria in the human body. They are believed to aid digestion and protect against certain gastrointestinal problems (e.g., diarrhea) and possibly other conditions or diseases. They may be especially helpful in stabilizing bacterial levels after the use of antibiotics, which can kill both harmful and beneficial bacteria present in the intestines. 

Probiotics and prebiotics may also be available in supplement form. However, most nutritional experts advise consumers to get their nutrients and other healthful substances, including probiotics and prebiotics, from food sources rather than supplements.

The use of probiotics and prebiotics is generally believed to be safe, although they may not be recommended for people with immune system deficiency, gastrointestinal damage, or for children or pregnant women. A few side effects (e.g., abdominal discomfort, bloating, flatulence) have been reported with the use of certain probiotics and prebiotics.

Probiotics and prebiotics are found in a variety of foods and are considered bioactive food components. They may also be available as dietary supplements. Probiotics and prebiotics combined in the same product are known as synbiotics.                             

Probiotics (“for life”) are live microorganisms (e.g., lactobacilli) that are considered beneficial to humans. These bacteria may help suppress the growth of potentially harmful bacteria in the human body.

Prebiotics (“before life”) are certain nondigestible substances (usually found in carbohydrates, such as fructo-oliogosaccharides) in foods or supplements that are used as fuel by beneficial bacteria already in the body.

Probiotics and prebiotics alter the level of microorganisms in the intestines. The number of bacteria normally present in healthy intestines is estimated to be in the trillions, made up of more than 500 different types of bacteria. Most are beneficial, although a small number may be potentially harmful. These beneficial bacteria are necessary to help fight infection and aid immune system functioning.

The beneficial bacteria in probiotics, fueled by prebiotics, may reduce the number of potentially harmful bacteria in the intestines in a number of ways. They may compete with them for nutrients, thus crowding out disease-causing bacteria. These beneficial bacteria may also produce substances that inhibit the growth of potentially harmful bacteria. They may also restore the balance of beneficial bacteria in the gut due to imbalance caused by disease, stress, poor diet or the use of certain medications (e.g., antibiotics). Probiotics and prebiotics may also aid digestion by slowing the digestive process and encouraging nutrient absorption. 

To be effective, beneficial bacteria in probiotics must be alive when consumed. This allows them to grow and develop in the intestines. They may be freeze-dried if taken in supplement form. These bacteria may die if exposed to heat, moisture or air. Some types of probiotics may need to be stored in the refrigerator. The packaging of probiotic products should indicate if active (live) cultures are present.

Prebiotics must be able to survive the gastric acid of the stomach and the enzymes produced during digestion. Because the human body is unable to completely digest these substances, they pass through the stomach and small intestine into the large intestine, where they stimulate the growth and activity of certain bacteria. Different types of probiotics may prefer particular types of prebiotics. For example, bifidobacteria probiotics may prefer fructose- or galactose-based prebiotics.

Taken together, probiotics and prebiotics are believed to significantly promote the development of beneficial bacteria in the gut. Probiotics and prebiotics are not considered nutrients because they are not necessary for the human body to function. Thus, no deficiency disease occurs due to a lack of probiotics or prebiotics in the human body.

Research regarding the effects of probiotics and prebiotics is ongoing. Due to the vast assortment of bacteria that exist in the intestines, it is difficult for researchers to determine which effects are specific to each type of bacteria. For example, it is unclear which bacterial strains in probiotics have potential beneficial effects on particular diseases or medical conditions.

In addition, when studying probiotics and prebiotics, many different factors must be controlled for reliable results. These factors include bacteria type, potency (amount of bacteria per dose), purity (presence of possible contaminating microorganisms) and disintegration properties of each type of bacteria. 

There are a variety of different probiotics and prebiotics that come from food sources. Some may also be available as dietary supplements.

Probiotics are certain types of live bacteria that are consumed to help restore balance to the levels of beneficial bacteria in the intestines.

Lactobacilli are the most common probiotic used in foods and supplements. These bacteria are considered beneficial because they may provide vitamins (e.g., vitamin K), lactase, and certain antimicrobial substances (e.g., acidolin, acidolphilin, lactocidin, bacteriocin). Specific strains include lactobacillus acidophilus and lactobacillus GG.

Bifidobacteria is another common probiotic. Less common types of probiotics include enterococci, bacilli, escherichia and saccharomyces boulardii (a type of yeast).  

Probiotics and prebiotics may be obtained through various foods. They are also available as dietary supplements.

Food sources of probiotics include:

• Certain cultured dairy products (e.g., yogurt). Products with live (active) cultures of beneficial bacteria are considered to contain probiotics. Yogurt typically contains probiotics.
  
  
• Certain fermented foods. This includes the fermented cabbage found in foods such as sauerkraut and kimchi.
  
  
• Modified foods. Various food products may be fortified with probiotics. This includes probiotic-fortified beverages, breakfast cereals, smoothies and energy bars. 

Food sources of prebiotics include:

• Asparagus
• Bananas
• Chicory
• Garlic
• Honey
• Jerusalem artichokes
• Leeks
• Onions, onion powder
• Shallots
• Soybeans
• Whole grains

The benefits of probiotics and prebiotics have not been scientifically proven. Research in the area is ongoing, but studies have been limited and results inconsistent. Additional research is needed to confirm any claimed health benefits.

Probiotics and prebiotics can help balance bacterial levels within the intestines. They may increase the amount of helpful bacteria and reduce amounts of harmful bacteria, which can aid digestion and absorption of nutrients, and may protect against certain gastrointestinal problems. Probiotics and prebiotics may be especially helpful in stabilizing bacterial levels after the use of antibiotics (which can kill both harmful and beneficial bacteria present in the intestines).  

Probiotics are believed to have an effect on the following symptoms, conditions or diseases:

• Diarrhea. Probiotics may help prevent the accumulation of infectious bacteria that can cause diarrhea. Their activity in the intestines may also slow the digestive process, helping to alleviate diarrhea associated with a variety of conditions (e.g., irritable bowel syndrome, Crohn’s disease). Probiotics have been studied the most for their possible use in helping alleviate diarrhea.
  
  
• Vaginal infections, bacterial vaginosis. The use of probiotics is believed to help alleviate symptoms of these conditions, although it has not been sufficiently studied.
  
  
• Lactose intolerance. The ability of probiotics to convert the lactose in dairy products to lactic acid may be helpful for people who are unable to digest lactose. Research regarding the effects of probiotics on lactose intolerance has provided conflicting results. More information is needed before conclusions can be reached.

Prebiotics may aid in the absorption of certain minerals (e.g., calcium, magnesium, zinc, iron), thus helping to improve bone mineralization. In addition, prebiotics act as a type of soluble fiber in the intestines, which can aid digestion. Some experts believe prebiotics may potentially offer health benefits against diseases such as cardiovascular disease and type 2 diabetes, as well as gastrointestinal diseases.

Some studies have indicated that prebiotics may boost immune system development in infants, possibly helping to prevent certain allergies. Human breast milk contains prebiotics, and some studies have indicated that breastfed babies have higher levels of beneficial bacterial in their intestines, which may help protect them against certain types of infections (e.g., rotavirus).

Another study found evidence that adding prebiotics to infant formula may lower a baby’s risk of eczema.

Meanwhile, researchers in Australia discovered that giving a baby probiotics may reduce the risk of necrotizing enterocolitis, an infection that sometimes kills the lining of the bowel in premature babies. And researchers in California are examining whether or not the use of probiotics helps delay or prevent asthma in children.

However, caution is generally advised regarding use of prebiotics and probiotics in newborns. Parents are encouraged to consult their child’s pediatrician before supplementing a child’s diet with probiotics or prebiotics.

Probiotics and prebiotics are generally considered safe. A few side effects have been reported, including abdominal discomfort and mild to severe flatulence.

Food sources of probiotics are considered more favorable to consumers than supplements because foods offer nutrition as well as the beneficial bacteria contained in probiotics. In addition, probiotic and prebiotic supplements (like all supplements) are not subject to the U.S. Food and Drug Administration (FDA) safety and approval process required for medications. Manufacturers are responsible for ensuring the safety of their supplements, and that their product claims are truthful and not misleading. Furthermore, manufacturers of probiotics and prebiotics are not required to ensure the standardization of active ingredients in these products. The ingredient amounts can vary widely both between different products and product batches. Consumers are advised to carefully check product labels, contact the manufacturer for more information, and consult their physician or registered dietitian before taking any type of dietary supplement.

Probiotics or prebiotics may not be recommended in the following circumstances:

• Immune system deficiency. Anyone with lowered immune system function should consult their physician before consuming any dietary supplements, including probiotics.
  
  
• Gastrointestinal damage. Patients with intestinal damage, especially those recovering from gastrointestinal surgery, or who experience bacterial overgrowth in the intestines, should avoid probiotics.
  
  
• Pregnancy. Women who are pregnant are advised to avoid probiotic supplements. Currently, there is not enough data to determine whether the use of probiotic supplements is safe during pregnancy.
  
  
• Children. Consumers are encouraged to consult their child’s physician before providing probiotic or prebiotic supplements to children under the age of 3 years.

There is limited research regarding possible interactions between probiotics, prebiotics and other medications, supplements or foods.

It is generally believed that the following may decrease the effectiveness of probiotics:

• Antibiotic use. Antibiotics and probiotics should be taken two to three hours apart because antibiotics may kill the live beneficial bacteria contained in probiotics.
  
  
• Alcohol use. Probiotics and alcohol should not be consumed at the same time because the beneficial bacteria in probiotics may be damaged by alcohol.

Some experts recommend the use of antacids an hour before ingesting probiotics to help the live bacteria survive stomach acid. Some have advised probiotics be taken with milk or other dairy products to help ensure survival of the beneficial bacteria in probiotics.

Probiotics may potentially affect the quality of other medications. For example, some research indicates that probiotics may reduce the effectiveness of certain medications used to treat digestive disorders (e.g., sulfasalazine), although more study is needed.

Preparing questions in advance can help patients have more meaningful discussions with health professionals regarding their conditions. Patients may wish to ask their doctor or registered dietitian the following questions related to probiotics and prebiotics:

1. Can probiotics help with any disease or medical condition I currently have?
   
   
2. Can they help prevent certain conditions or problems I may be likely to get?
   
   
3. What type of probiotic is most appropriate for me?
   
   
4. Do you recommend I take a probiotic supplement? Why or why not?
   
   
5. Will probiotic supplements interfere with any medications or other supplements I am currently taking?
   
   
6. What amount of probiotics should I consume?
   
   
7. How can I be sure the probiotics contained in foods or supplements are alive?
   
   
8. What type of prebiotic is best suited for the type of probiotic I am taking?
   
   
9. What foods contain this type of prebiotic? How much do I need to consume on a daily/weekly basis?
   
   
10. Do you recommend I take a prebiotic supplement instead of getting it from foods?