Dr. Greene, my daughter often gets yeast infections. I've heard that active-culture yogurt can prevent or treat vaginal yeast infections and also diarrhea. Is this true? Or is it just an old wives' tale?
Palo Alto, California
One of those ideas is true and one is not, but the larger truth about yogurt may surprise you!
In school, my daughter is studying the diversity of ecosystems from the Great Barrier coral reef near Australia to the equatorial rainforests of the Amazon River basin. Her eyes widened when I described to her the amazingly complex ecosystem hidden in the dark recesses of our intestines.
As many as 500 different species of bacteria form a society there, in a delicate balance with each other and with their ‘earth’ – us. We are outnumbered in our own bodies1 – there are more bacterial cells in us and on us than there are human cells. The beneficial bacteria produce critical enzymes that we need for our health. When everything is going well, we all benefit.
But sometimes things don’t go so well. When we take an antibiotic, it can be like clear-cutting rainforest land. Entire species are eliminated. It’s a devastating emergency for the species there.
The short-term results of taking antibiotics include diarrhea (comparable to erosion) and yeast infections (as more primitive species takes over the vacated niches).
The opposite of antibiotics are probiotics – a term coined in 1965 to describe substances that favor the growth of beneficial microorganisms in the body.2
The idea of giving yogurts and fermented milks to promote health has been around for millennia3 – far older than most old wives’ tales. Buttermilk, feta cheese,4 and active-culture yogurts are among the foods that have been used. Almost a century ago, Russian microbiologist Elie Metchnikoff suggested that consuming the live microbes infermented milk products may be, at least in part, responsible for the longevity of certain ethnic groups.5
Is this quackery or solidly scientific? A flood of recent research made probiotics a hot topic at the World Congress on Pediatric Gastroenterology, Hepatology, and Nutrition in August 2000. Two species of probiotics, Bifidobacterium and Lactobacillus, have been the most studied
Some benefits have been well established for some time. Bacteria that produce the enzyme lactase will help reduce lactose intolerance.6 Probiotics can treat other enzyme deficiencies (e.g. sucrase maltase deficiency) as well.7
Could probiotics be used to counteract episodes of diarrhea that are caused by antibiotics? In a placebo-controlled study, Lactobacillus was given to children along with antibiotics, resulting in fewer cases of diarrhea and milder diarrhea for those who did get it.8
How about treating other types of diarrhea? Active-culture foods are somewhat effective at preventing and treating bacterial diarrhea, including Clostridium,9 Shigella, Salmonella,10 and the dreaded E. Coli 0157:H7.11
It makes sense that active cultures should help diarrhea caused by either destruction of beneficial bacteria or by invasion of disease-causing bacteria. But viral diarrhea takes place on a different playing field. Surprisingly, Lactobacillus is most effective at preventing and treating rotavirus and other viral infections.12This suggests that probiotics are not just friendly placeholders in the gut, but active immune enhancers.
Indeed, randomized, double blind, placebo-controlled trials have found significant, measurable increases in markers of immune function in those with active cultures in the diet.13 Perhaps it would be better to say that probiotics modulate the immune response – keeping it in the normal level — by also protecting against inflammation and autoimmunity.14
By reducing inflammation, probiotics appear to be useful in treating a variety of gastrointestinal problems including inflammatory bowel disease (such as Crohn’s disease or ulcerative colitis), ulcers,15 and irritable bowel syndrome.16 Flatulence and non-specific tummy aches can also be decreased.17
But the effect goes far beyond this….
Food allergies are caused by the production of antibodies (IgE) against something in the diet. Normally, a substance in our bodies called interleukin 12 (IL-12) prevents this. A recent study showed that consuming Lactobacillus can increase IL-12, decrease IgE antibodies18, and thus help prevent and treat food allergies.19
Many children with eczema have flare-ups triggered by what they eat or drink. In one fascinating study, a group of children who received Lactobacillus had significant improvement of their eczema within one month!20
Lactobacillus in yogurt also has a weakly protective effect against asthma by stimulating interleukin and TH 1 cells.21 (It has some gentle anti-tumor properties by the same mechanism22.) Some evidence suggests that the recent increase in childhood asthma may be partially from the destruction of our normal, healthy bacteria.23
And in at least one study of 571 children, there was a significant reduction in respiratory infections (including sinusitis, bronchitis, and pneumonia) in the children taking Lactobacillus.24
One of the most startling recent studies of Lactobacillus indicated a “marked, long-term” protective effect on the heart, preventing and decreasing damage from lack of oxygen to the heart muscle. The effect was attributed to the demonstrated changes in inflammation and the immune system.25
A recent double-blind, placebo controlled trial found that some strains of active-culture yogurt, eaten over 8 weeks, help lower LDL cholesterol and normalize blood pressure.26 Serum triglycerides were also lowered in a controlled animal study.27
A healthy internal environment of beneficial bacteria can also protect the body from toxins. Aflatoxin, a highly toxic substance found in foods including peanut butter and alfalfa sprouts, can be intercepted by Lactobacillus.28 Probiotics can protect against food poisoning.29 Similarly, a diet high in Lactobacillus can block much of the liver damage that would be caused by excess alcohol.30
Because probiotics can decrease the presence of carcinogens in the intestines in several ways, they may prove helpful for preventing cancer.31 This would protect against colon cancer32, as one might expect, but the effect may extend to other cancers as well. One important study suggests that in the soy-rich Japanese diet that seems to prevent breast cancer, it is the abundance of the probiotic Bifidobacterium in some soy products that is at least partly responsible for the powerful preventive effect33. This will be an important area of study in the future.
Along the same lines, it may be the Lactobacillus in wine that is responsible for some of the health benefits.34
Breastfeeding provides numerous health benefits. Interestingly, breastfed infants have high concentrations of protective Bifidobacteria and Lactobacillus in their gastrointestinal tracts35, while in formula-fed babies streptococcus foecalis and E. Coli are at high levels.36 Promoting beneficial bacteria may be one of the important ways that breastmilk protects against gastrointestinal tract infections, otitis media, invasive Haemophilus influenzae type b infection, RSV infection, and other causes of upper and lower respiratory tract infections.
After a child is weaned, there are other foods (such as chicory37 and green tea38) that promote beneficial bacteria. Most kids will turn up their noses at those – but not at honey. Back in medical school, I was taught that there was no difference between honey and table sugar. It turns out, though, that (among other things) there is a difference in the intestinal population of those who use the two different sweeteners. Honey increases Lactobacillus in the gut.39 Other substances, most notably cigarette smoke,40 can decrease Lactobacillus. I expect that the chlorine in unfiltered tap water also affects the ecosystem within, but I have not yet come across credible studies on the subject.
While active-culture yogurt has proven helpful in many areas, and seems to be helpful in many others, it appears to do nothing to combat vaginal yeast infections. It has been recommended both orally and topically, but when evaluated no benefit is found. 41 Perhaps this is because the normal population of Lactobacillus continues to thrive in the vagina even during a yeast infection.42
Lactobacillus can help prevent yeast, though, in the GI tract, diaper area and in the mouth.43 Probiotics can also help to prevent urinary tract infections.44
Yogurt and other active culture foods are not a panacea, but they are significant gentle helpers. They help create and protect the teeming intestinal ecosystem found in breastfed kids. The beneficial bacteria form a silent protective barrier against invading organisms, toxins, and carcinogens. Beyond that, the latest research shows that they actively kill invaders45 and neutralize toxins. And beyond even that, they actively fine-tune our immune systems.
These are wonderful foods to include in your child’s regular diet. But not all yogurts are created equal. I recommend choosing organic yogurt with a healthy variety of active cultures to promote biodiversity in the gut. The more different types of healthy bacteria, the better!
Whenever antibiotics are necessary, it makes sense to take probiotics as well. I believe that there should be at least as many “prescriptions” for probiotics as there are for antibiotics. I also hope that they will be added to many oral rehydration solutions46 so that kids can get their benefit when diarrhea is at its worst.
One night last month I set my alarm for 2 o’clock in the morning. I stumbled out of my hotel room bed to watch a spectacular sight – a neighboring hotel being demolished. The planned implosion was over in seconds and was something I will not soon forget. The power to destroy is flashy; the power to create is often quiet. It took much more to build that hotel than to tear it down.
The next day I saw the implosion many times on the news, at different speeds and from different angles. I expect I’ll see the footage used in a movie someday. But there were no news stories showing the quiet drama of the large team working together over time to craft that hotel.
Bad news captures the headlines while truly powerful good news is often slower and less obvious. The same is true for bacteria. Germs that cause human disease have dominated scientific journals and the popular press. But the marvelous microcosm hidden within the human digestive system is a greater power – one that we could not live without.