Top | Health+Food

Probiotics, unpacked

(article, Catherine Bennett Dunster)

[%pageBreakSettings nobreak=true][%adInjectionSettings noInject=true]

p(blue). Editor's note: Catherine Bennett Dunster wrote the Health+Food column from June 2007 to April 2008.

I keep hearing about “probiotics.” Could you explain what they are exactly and talk about their benefits?

Probiotics — live microorganisms that can be found in food and dietary supplements — are beneficial to humans and thus are often referred to as "friendly bacteria." If consumed in large-enough quantities, probiotics may provide health benefits. Technically, such live microorganisms include yeasts, bacteria, and viruses, but consumers are most familiar with the probiotic bacteria resident in the cultured-milk products yogurt and kefir. 

h1.Different strains, different benefits


In the U.S., yogurt must contain the bacteria strains Lactobacillus delbrueckii bulgaricus and Streptococcus salivarius thermophilus. Supplementary strains (such as Bifidobacterium or Lactobacillus acidophilus) are often added later to enhance the yogurt's health effects or taste.

Does your yogurt brand contain the right amount of viable cells of the correct bacteria to back up its claims? A recent class-action lawsuit is taking Dannon to task on this very issue.

Current evidence suggests some beneficial probiotic effects are strain-specific. Lactose intolerance may be the one exception to date, as more than one probiotic strain seems to decrease symptoms.  

It's also unclear how processing affects probiotic quality. Can the bacteria still have a therapeutic effect? And which bacteria strain — and at which dose and frequency — addresses your specific health concerns? The scientific jury is still out on these questions.


With the recent flood of probiotic bacteria added to everything from fruit juice to breakfast cereals, food marketing has made the names Lactobacillus and Bifidobacterium_ almost as familiar as Brad and Angelina. 

Historically — and prior to modern food processing — fermented beans, vegetables, grain products, and alcohol were widely consumed, as were cultured dairy products. Fermenting foods is a way to prolong their shelf life. The fermenting process also creates incredibly complex flavors, represented around the globe in myriad cuisines. Yogurt is the only one you can think of? What about sourdough or miso? Kimchee, sauerkraut, or fermented pickles? Or the favorite of my friend Melisa: dosas. All are fermented and rich in probiotics.  

Once consumed, probiotics that survive the harsh environment of the stomach and move into the intestines are quite diligent. They help maintain a balance with the other types of bacteria naturally located in the stomach, assist in breaking down food, synthesize vitamins, and process hormones — estrogen, for example. We don’t fully understand exactly how probiotics operate, but we know enough to hypothesize about their potential advantages. 

At first glance, like other food components spotlighted in the media, probiotics appear to be the answer to everyone’s nutrition prayers — tasty and good for all that ails you. (Or good for preventing what someday might ail you — or your spouse/children/aging parents/backyard hens.) Popular health claims for probiotics include:

list(compact inside).
 preventing gastrointestinal cancer 
 supporting the immune system 
 reducing lactose intolerance 
 reducing asthma and eczema
 minimizing antibiotic-induced diarrhea
 maintaining healthy gut flora (the naturally occurring bacteria located in the gastrointestinal tract) 

Many of these health claims have yet to be bolstered by adequate research. There is, however, scientific documentation that shows some probiotic strains do help those suffering from lactose intolerance to digest lactose, the primary sugar in milk. In addition, some probiotics have been shown to decrease the incidence or duration of intestinal infections and antibiotic-induced diarrhea.  

The other health claims above are supported by isolated preliminary evidence. It’s promising, but just not deep or definitive enough to deem conclusive. We need more clinical research in the form of double-blind, randomized, controlled trials. And most importantly, this research should utilize strains and doses of probiotics that actually reflect those present in foods at the time of consumption. 

[%image reference-image float=right width=400 credit="Photo: iStockphoto/adlifemarketing" caption="Fermented foods such as pickles are full of beneficial probiotic bacteria."]

(Sadly, food marketers often cite research using one strain or level of probiotic while the food they’re touting contains an entirely different strain, or lesser amounts of the same probiotic. Or the strain and amount may be the same as in the touted research, but the levels in the food product at the time of consumption are inadequate due to aging or storage issues.) 

Since microorganisms are essentially “herd animals” — meaning they travel together — this type of research can be difficult and expensive to conduct. 

In tandem with today’s immediate-gratification mentality, there are plenty of attempts to market and sell foods as functional foods — i.e., as foods with a potential health benefit. (For more on that, read Michael Pollan’s new book, In Defense of Food.) I’m all for getting the most out of every mouthful, but until the health claims are backed up by sufficient research, I recommend eating traditional fermented and cultured foods because they taste delicious and provide foundational nutrients as part of an overall whole-foods diet.  

That said, if you suffer from lactose intolerance and the right brand of yogurt alleviates your symptoms, or you’ve had good luck avoiding diarrhea by chasing your antibiotics with yogurt — dish up! Otherwise, enjoy these tasty foods because, well, they taste good.

p(bio). Catherine Bennett Dunster is a registered dietitian and a former instructor at Oregon Health and Science University. She lives with her husband and two children in Portland, Oregon. 

Please send your nutrition questions to

reference-image, l

feed-image, l