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Friendly Bacteria

A Primer on Probiotics

By Beth Bence Reinke, MS, RD
Guest Writer Bacteria for breakfast – it’s the newest health kick. More and more people are trying probiotic-infused dairy products, each spoonful teeming with microscopic critters that promise to contribute to good health.

What are probiotics?

Probiotics are living, single-celled microbes that provide a health benefit when taken in adequate amounts. These “friendly bacteria” are added to foods during processing or put into capsules or powders that are sold as supplements. Dairy products like yogurt, kefir, and buttermilk are the most common probiotic-enhanced foods, but others are flooding the market such as infant formula, juice, cereal, and even candy bars. Other foods that ordinarily contain probiotics include cottage cheese, tempeh, miso, soy sauce, and fresh sauerkraut.

Television commercials advertise newfangled yogurts and smoothies with probiotics that promote “regularity,” making them seem like modern health foods. On the contrary, cultured milk products have a long history of promoting health.

Historians believe dairy products like kefir and yogurt were consumed by God’s people throughout Bible times. More recently, a 19th century Russian immunologist linked the long, healthy lives of Bulgarian peasants to their intake of fermented milk.

Are prebiotics the same as probiotics?

No. Prebiotics are dietary substances that serve as food for the probiotic bacteria. Common prebiotics include inulin, oligofructose, and lactulose. Prebiotics are found naturally in foods like onions, garlic, oatmeal, honey, wheat, barley, legumes, bananas, berries, leafy greens, and leeks. Some probiotic-infused dairy products have prebiotics added to help the friendly microbes survive in the intestinal tract. Added prebiotics should be listed on the ingredients label.

Probiotic names

Probiotics have hard-to-pronounce scientific names. The most common ones are Lactobaccillus and Bifidobacterium. A type of bacteria called Streptococcus thermophilus is often used as a yogurt starter culture. Each type of probiotic bacteria is identified by three names: genus, species, and strain. Here is an example: Bifidobacterium infantis 35624. Genus and species are in italics and the number designates the strain. On food labels the genus is sometimes abbreviated with just a capital letter like this: B. infantis 35624.

Why eat bacteria?

The main reason to use probiotics is because they increase the "good bacteria" in the gut. These microbes, trillions of them in the small and large intestines, play key roles in digestion and immune function. Sometimes the normal gut bacteria, also called intestinal flora, are disrupted by antibiotics or illness. A number of the good flora may be wiped out and “bad” bacterial overgrowth may result, causing diarrhea and other gastrointestinal miseries. Adding back some good bacteria via probiotics helps normalize bacterial colonization. That’s why doctors recommend eating yogurt with antibiotics. 

The intestines are vital to the immune system because more than half of the body's immune cells are in the intestinal walls. Bringing balance to the gut flora helps maximize immune function. 

Health benefits of probiotics

Numerous claims are made on behalf of probiotics, but many of the so-called health benefits are not yet substantiated by research in human subjects. According to the World Gastroenterology Organisation (the correct European spelling), there is adequate evidence to utilize probiotics for:

  • acute infectious diarrhea
  • antibiotic-associated diarrhea
  • irritable bowel syndrome
  • lactose intolerance
  • prevention of atopic dermatitis (eczema)
  • boosting immune function

Are all probiotics alike?

Definitely not. There are a couple of things to keep in mind about how probiotics work. First, they may not work the same for everyone. Each person has a distinctive pattern of bacterial flora in his or her intestines, so a certain probiotic may not have the same benefit for you as it will for someone else. Some people who try probiotic supplements get positive effects in as little as a week or two. For others, it may take a month or two to see results.
Second, the benefits of probiotics are strain-specific. If a study shows that one strain of probiotic bacteria prevents infections, it does not mean that all probiotics prevent infections. One strain may help with allergies while another may treat diarrhea. For example, the strain L. acidophilus LA-5 may have different effects than the strain L. acidophilus NCFM.

Are they safe?

Most food sources of probiotics, like yogurt, kefir, and cereal, are probably safe for most healthy people. A doctor should be consulted before giving probiotics to young children, the elderly, and anyone with a medical condition or compromised immune function. Researchers have already identified one medical condition where probiotics can do more harm than good: in a study of patients with acute pancreatitis, using probiotics doubled their risk of dying.

What is the recommended dose?

At this point, no general recommendations can be made for how much to take or eat. Most human studies used daily dosing of probiotics, whether in food or supplement form. Studies showed effective doses between 100 million and one billion colony forming units (CFUs). Dose depends on which strain is used and what health benefit is desired. Anyone who is considering taking a probiotic supplement, should consult a physician for dosage recommendations.

What should I look for on the label?

Existing labels on some probiotic-infused dairy products give very little information. Ideally, the label would tell you the genus, species, and strain of each probiotic in the food. It would also cite human studies conducted on that particular product or strain. There should also be a date indicating how long the probiotic is effective and assurance that the bacteria will survive until that date. If probiotics continue their surge in popularity, manufacturers may be required to make the labels more consumer-friendly.

Yogurt anyone?

Our knowledge of probiotics is in its infancy. There is much to discover about how added bacteria interact with normal intestinal flora. Perhaps future studies will demonstrate more ways probiotics can promote good health.
For now, eating a cup of low-fat yogurt with live active cultures and probiotics is probably a wise move for most healthy people. At the very least, you get protein, calcium, vitamin D, and other nutrients along with the friendly critters. Bacteria for breakfast – why not?

Douglas, Linda C., PhD, RD and Mary E. Sanders, PhD. "Probioitics and Prebiotics in Dietetics Practice. Journal of the American Dietetic Association, March 2008, Vol. 108, No. 3; 511-520.

Guarner, Francisco, "Probiotics and prebiotics." World Gastroenterology Organisation Practice Guidelines. World Gastroenterology Organisation, May 2008.  Accessed 10/28/08.

Palmer, Sharon, RD. "Happy Entrails: A Close Look at Digestive health Claims." Today's Dietitian, May 2008; 29-32.

"Probiotics and Prebiotics." RD411 Web site. Accessed 9/24/08.

Sanders, MaryEllen, PhD. "Quick Reference Guide to Probiotics." September 2008.  Accessed 10/28/08.

"Understanding Probiotics." RD411 Web site.  Accessed 6/4/08.

Beth Bence ReinkeBeth Bence Reinke is a registered dietitian who writes about food, nutrition, and health topics. She is a mom of two sons and the author of numerous magazine articles for adults and children. Beth and her husband have been CBN partners since 1998. Visit her at .

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