Probiotics and Prebiotics

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Probiotics and Prebiotics

If you’re someone who likes to keep up with the latest in food and nutrition, you’ve undoubtedly heard or read about probiotics and prebiotics. You might know that they can aid digestion and reduce bloating, as touted in countless yogurt commercials on TV. But perhaps you didn’t know that they have numerous other potential health benefits. You might even be shocked to learn what probiotics really are: bacteria. Prebiotics, on the other hand, are the food that probiotics need to survive. While this knowledge might make some people squeamish at first, it is a necessary first step toward understanding the helpful role probiotics can play in the body. This article describes what probiotics and prebiotics are, how they can help you, and how they might in some cases be harmful — so that you can have a better idea whether adding them to your diet is right for you.

Probiotics are our friends

If the thought of bacteria coursing through your digestive system makes you squirm, take a deep breath and realize this: Some types of bacteria are good for us. We tend to hear much more about all of the harmful bacteria that can cause illness, such as Streptococcus pyogenes, which causes strep throat; or Escherichia coli, which can cause serious food poisoning. Often overlooked are all the good types of bacteria that help keep our bodies functioning properly and can even help ward off certain diseases.

The World Health Organization (WHO) defines probiotics as “living organisms which, when administered in adequate amounts, confer a health benefit on the host.” Microorganisms include bacteria, viruses, and yeasts — organisms that can only be seen with a microscope. While some varieties of yeast may confer a health benefit, the most common probiotics are certain types of bacteria.

Scientists estimate that about 500 different species of bacteria live in and on our bodies. In the typical human gut, there are about 100 trillion microorganisms belonging to these 500-odd species. The large intestine has the most bacteria due to its position as the “last stop” in the digestive system; here, bacteria break down certain molecules for energy that human digestive enzymes cannot. It takes several hours for digested food to travel the length of the large intestine, giving the bacteria there plenty of time to grow and thrive. The good news is that most of these microorganisms serve to protect us from harmful bacteria, as well as to aid in digestion, nutrient absorption, and immune function.

Think of probiotics as friendly bacteria. The word “probiotic” means “for life,” and as the name suggests, we all rely on these organisms to maintain optimum health.

Probiotic history

Probiotics are nothing new; foods containing them have been around for thousands of years. Persian tradition attributes the prophet Abraham’s long life to drinking soured milk. The Romans described using fermented milk to treat intestinal gas. An early clinical account describes how Francis I of France, king during the 1500’s, suffered from diarrhea that was cured only when a doctor sent by the Ottoman sultan gave him yogurt. (Learn more about yogurt here.) Elie Metchnikoff, a scientist who won the Nobel Prize in Medicine in 1908, studied peasants in Bulgaria who lived longer than 100 years. He deduced that their good health and long lives were due to a microbe in a type of yogurt that they ate; he subsequently named this type of bacteria Lactobacillus bulgaricus. Fermented milk products, once rare outside the Middle East and southwestern Europe, have caught on in western Europe and the United States in the last century due to their introduction by immigrants and increasing knowledge of their health benefits.

Probiotics and health

Probiotics can benefit human health in a number of ways that are well established:

Boosting the immune system. If your immune system isn’t in tip-top shape, you’re more vulnerable to harmful microorganisms (bacteria, viruses, yeasts, and fungi) that can lead to illness. People with uncontrolled diabetes may have a compromised immune system, as constant high blood glucose levels have been shown to weaken immune defenses. But just as certain behaviors — not getting enough sleep, working long hours at a stressful job — can weaken your defenses, you can boost your immune system through proper rest and good nutrition. Researchers believe that including probiotics in your diet can help bolster the immune system to fight off disease.

How probiotics can help: Good bacteria may somehow communicate with immune cells in the digestive tract to launch an attack against harmful invaders. They may also “crowd out” harmful bacteria by taking up space and food, thus limiting the invaders’ ability to thrive.

Counteracting antibiotics. Antibiotics are a double-edged sword. On the one hand, they help get rid of certain infections — including strep throat, tuberculosis, salmonella, and bacterial meningitis — by killing off harmful bacteria. On the other hand, they also kill off good bacteria throughout the body, including the digestive tract, the urinary tract, and reproductive organs. As a result, one infection may be swapped for another, such as antibiotic-induced diarrhea or a yeast infection in the mouth or vagina.

How probiotics can help: Taking probiotics has been shown to reduce antibiotic-induced diarrhea and may be helpful for women who get vaginal yeast infections whenever they take an antibiotic.

Alleviating lactose intolerance. Lactose intolerance — the inability to digest lactose, a type of sugar found in dairy products — affects up to 50 million Americans. This condition occurs due to a lack of lactase, an enzyme needed to break down lactose in the digestive tract. Symptoms can range from mild to severe and may include abdominal cramping or pain, gas, bloating, nausea, or diarrhea.

How probiotics can help: The Lactobacillus genus of bacteria (which includes many different species) converts lactose into lactic acid. This is why some people with lactose intolerance can eat yogurt or drink acidophilus milk without experiencing side effects.

Fighting irritable bowel syndrome. Irritable bowel syndrome (IBS) is one of the most common digestive disorders and one of the most frustrating to treat. IBS isn’t a disease, but rather a general term to describe a malfunctioning digestive system. People with IBS may have different symptoms at different times, including cramping, pain, bloating, diarrhea, and constipation. There are few medicines available to treat IBS. Some people find relief by making dietary changes, such as eating more fiber, cutting out caffeine and alcohol, and avoiding refined carbohydrates. Stress reduction, exercise, yoga, and massage may also help.

How probiotics can help: It’s a bit of a mystery how probiotics work to reduce IBS symptoms, but supplements that contain the bacteria Bifidobacterium infantis seem to help with bloating, pain, and bowel regularity. One study showed that a multibacterial probiotic reduced diarrhea in 84 people with IBS compared with those given a placebo (inactive pill).

Preventing urinary tract infections. Urinary tract infections, or UTIs, can be caused by a number of types of bacteria, including E. coli. UTIs are much more common among women than men. Women who have diabetes are also two to three times more likely to have bacteria in their bladders than women without diabetes. Having diabetes might make a person more susceptible to getting a UTI in part because the white blood cells — part of your immune system — don’t work as well to fight off bacteria. It’s also possible that in some people with diabetes, the bladder does not contract as well as it should — which means that some urine stays in the bladder, forming a breeding ground for bacteria.

How probiotics can help: Consuming two specific strains of bacteria (a strain is a subtype of a species) — Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 — has been shown to help restore good bacteria to the urogenital tract in women, reducing the incidence of both UTIs and vaginal infections.

Combating C. difficile infection. If you or someone you know has ever been hospitalized, you might be familiar with a common infection caused by bacteria called Clostridium difficile, or C. diff for short. C. diff infection usually sets in after a course of antibiotics. Not everyone actually gets sick from this bug, but in those who do, typical symptoms include watery diarrhea, abdominal pain, fever, blood or pus in the stool, nausea, and dehydration. Symptoms can be mild or very severe. In extreme cases, kidney failure, bowel perforation, and even death can result. C. diff infection is common in hospitals and other health-care facilities and is thought to be spread by workers who don’t adequately wash their hands. People who are healthy usually don’t get sick from C. diff, but if you’re ill and given antibiotics, the antibiotics may wipe out the good bacteria that can keep C. diff under control. New strains of C. diff make it difficult to treat; not all antibiotics work on all strains, and some may make the infection worse.

How probiotics can help: Fortunately, several types of probiotics have been shown in studies to prevent or reduce diarrhea caused by C. diff infection. A probiotic yeast called Saccharomyces boulardii, along with antibiotics, may also help prevent recurrent C. diff infection.

Other ways probiotics may help

Researchers are also studying probiotics for other possible health benefits. For example, probiotics may be helpful in preventing and treating eczema in infants. They also may play a role in protecting against colon cancer, although it’s too early to recommend them on that basis. Probiotics may also be beneficial for treating kidney stones, lowering the risk for heart disease, reducing inflammation linked to arthritis, and even fighting cavities.

Probiotics may turn out to be helpful in the fight against obesity. In one study, pregnant women who were given probiotics and dietary counseling throughout their pregnancy, starting in the first trimester, had less body fat a year after giving birth than women who were given a placebo and dietary counseling during pregnancy. In another study, mice were fed an engineered strain of Lactobacillus that was found to change the composition of their fat tissue. While there’s currently not enough evidence to recommend consuming probiotics for weight loss, studies such as this one suggest that scientists may eventually be able to engineer bacteria that can change a person’s metabolism for the better. Future research will most certainly uncover even more uses for, and benefits from, probiotics than we know of today.

A particular strain of bacteria called Bifidobacterium bifidum CECT 7366 may be useful in treating peptic and duodenal ulcers caused by H. pylori infection, which can be difficult to treat using antibiotics. Studies have so far been done only in mice, so many more studies in humans are needed before this probiotic can be considered a viable treatment for ulcers.

Probiotic foods

Certain foods contain probiotics that either occur naturally in the food or are added during processing. Food sources of probiotics include the following:

• Yogurt
• Kefir (a cultured drink that is similar to yogurt)
• Acidophilus milk
• Buttermilk
• Sour cream
• Aged cheeses (Gouda, Swiss, etc.)
• Cottage cheese that contains active cultures
• Miso (a fermented soybean paste)
• Tempeh (a fermented soybean product)
• Sauerkraut

Other foods that may contain added probiotics are certain varieties of cereal, juice, frozen yogurt, and even candy. According to the website, foods that have added probiotics usually contain Lactobacillus or Bifidobacterium bacteria, or Streptococcus thermophilus. One way to tell if a food contains probiotics is to look for the phrase “live and active cultures” on the package. Some foods may contain more than one type of probiotic. For example, yogurt in the United States must be made with two types of bacteria, Lactobacillus bulgaricus and Streptococcus thermophilus. Stonyfield Farm yogurt contains four other strains, as well: L. acidophilus, Bifidus, L. casei, and L. rhamnosus. Some varieties of yogurt may be heat-treated, which prolongs their shelf life but can kill off their probiotics. These varieties will not carry a “live and active cultures” seal.

One side benefit of eating foods that contain probiotics is that many of them have a low glycemic index, thanks to the acid-producing bacteria they contain. This means you’re less likely to experience a spike in your blood glucose level after eating these foods compared with others with a similar carbohydrate content.

Probiotic supplements

Probiotics are also available as capsules, tablets, powders, and liquids. Like other dietary supplements, probiotics are not regulated by the U.S. Food and Drug Administration (FDA). If you’re considering taking a probiotic supplement, talk with your health-care provider first. Probiotics may not be safe for people with certain medical conditions. Here are a few tips for choosing and using probiotic supplements:

• Don’t stop using prescribed medicines — unless your doctor tells you to stop — just because you’re taking a probiotic.

• Choose a supplement manufactured by a reputable company.

• Choose a supplement that is uncentrifuged, which is a process that can destroy living cells. Look for the word “uncentrifuged” on the supplement, or contact the company directly to inquire about processing methods.

• There is likely benefit from choosing a supplement with multiple types or strains of bacteria. Ideally, the types of bacteria and amounts per dose should match what was used in research studies of the supplement. A product’s website will often provide information on these details.

• Capsules are the best form of probiotic supplements because of the protection they offer against heat and moisture.

• Always check the expiration date before buying – and before using – a supplement.

• Some supplements may require refrigeration; read the label to see if this is the case.

• A probiotic supplement should contain at least 1 billion live cells per gram and may contain upwards of 10 billion, although more is not necessarily better. The upper limit should be based on doses used in clinical research.

Another option when choosing a supplement is to look for the number of CFUs (colony-forming units) on the label. This number is another way to indicate the amount of live microbes in the product. In general, a dose of about 20 billion CFUs is suggested.

• If you have any side effects from a probiotic supplement, stop taking it and contact your doctor.

Safety concerns

The use of probiotic supplements in the United States is still relatively new, and there’s a lot we don’t know about their long-term effects. As is the case with many dietary supplements, their safety hasn’t been thoroughly studied. And it’s particularly unclear how safe they are for children, the elderly, pregnant women, and people with compromised immune systems. Foods that contain probiotics are more clearly safe than supplements, given that they have been safely consumed for thousands of years. However, people with severely compromised immune systems — such as those with HIV or AIDS, or who are undergoing chemotherapy or radiation — should consult their health-care team before consuming any food or product containing probiotics. Probiotics may also be inappropriate for people with organ failure or who are in the ICU. In one clinical trial, 24 people with severe pancreatitis died after being giving probiotics.


Prebiotics are indigestible nutrients that serve as food for probiotics. Since humans don’t digest prebiotics, these nutrients pass through the digestive system until they are fermented in the large intestine by bacteria. Prebiotics are what allow probiotics to thrive.

Besides being a food source for probiotics, prebiotics may have some health benefits of their own, including the following:

• Enhancing absorption of minerals, such as calcium, iron, and magnesium
• Promoting healthy bowel function and regularity
• Inhibiting growth of cancerous lesions in the digestive tract
• Improving the funtioning of the immune system
• Lowering blood cholesterol levels

There are many natural dietary sources of prebiotics. The following foods are especially good sources:

• Asparagus
• Jerusalem artichoke
• Bananas
• Onions
• Garlic
• Leeks
• Chicory root
• Wheat bran
• Oatmeal
• Flax
• Barley

Prebiotics may also be added to foods like cottage cheese, yogurt, yogurt drinks, cereals, granola bars, and pasta. Food ingredients that act as prebiotics — but may or may not be proclaimed as such — include the following:

• Inulin (don’t confuse this with insulin!), a type of fiber

• Fructooligosaccharides, which consist of connected sugars

• Galactooligosaccharides, which result from certain enzymes acting on lactose (“milk sugar”)

• Polydextrose, a synthetic type of fiber

• Maltodextrin, derived from corn, rice, or potato starch

• Lactulose, a synthetic indigestible sugar

• Resistant starch, called this because it resists digestion (found naturally in cooked and cooled starchy foods such as pasta salad)

Like probiotics, prebiotics are available as supplements, usually in capsule or powder form. These supplements most commonly contain inulin, chicory root extract, polydextrose, or oligosaccharides. It’s probably best, though, to get your prebiotics from natural food sources, since many of these foods contain fiber and other important nutrients. There is no established recommended daily level of consumption for prebiotics. Some studies suggest that aiming for 5–15 grams daily is a good idea; Americans actually get about 1–4 grams each day on average. Foods that contain added prebiotics usually provide 2–4 grams per serving.

Prebiotics are generally considered to be safe. Common side effects include gas, bloating, and cramps, especially if you suddenly increase your intake of prebiotics; it’s best to gradually increase your intake. Remember that while prebiotics themselves do not affect blood glucose level, if they’ve been added to a food that contains carbohydrate, they may slow or otherwise change the digestion of that food’s carbohydrate.

A win-win situation

Both probiotics and prebiotics play a vital role in sustaining good health. Whether through supplements or simply through dietary changes, you may find that adding these living organisms — and their food — to your diet ends up making you a happier organism, as well.

Originally Published December 5, 2011

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