Q. Do probiotics really work?

A. Probiotics are “friendly” bacteria found in the gut that help us digest foods and fight harmful bacteria. They also include live, active cultures used to ferment foods like yogurt and sauerkraut. Reputed to improve digestion and boost immunity, foods that contain probiotics have been appearing more and more on supermarket shelves. First came yogurt enhanced with special probiotic strains. But the trend has spread quickly, and now cottage cheese, energy drinks, snack bars and cereals advertise high levels of beneficial bacteria too.

The good news is that advances in food processing make it likely that probiotics get to the gut where they can tip the balance of bacteria in a healthy direction. “Companies have developed technologies that allow bacteria to resist the temperatures and pressures of manufacturing as well as the heat and acidity in the stomach,” says Ralph Felder, M.D., Ph.D., author of just-out The Bonus Years Diet (Putnam).

The bad news is that there are thousands of probiotic strains; only a handful have been clinically tested. Manufacturers don’t always list the strain, or amount, of bacteria added. Plus, individuals respond differently to various strains, so what works for one person may not work for another, says Jeannie Moloo, Ph.D., R.D., spokesperson for the American Dietetic Association.

If you’d like to try probiotic products, your best bet is yogurt with a “Live & Active Cultures” seal (regulated by the National Yogurt Association), which marks a product that meets a specified level of “friendly” bacteria. The absence of a seal doesn’t mean a probiotic-enhanced food is ineffective (only yogurts are eligible), and often it pays to test several. “If one isn’t providing benefits after a couple of weeks, try another,” suggests Moloo.


I have been taking a probiotic from cvs pharmacy and it is a hard golf bb sized pill. It has done wonders for me. I'm a career dieter and actually stopped working out so I would not continue to lose weight. I still manage to maintain my weight with little to no effort. Daily I take a 1.5billion cells probiotic, one activia and eat a fiber bar.


03/22/2013 - 10:23am

Before someone can answer yes or no to "does it work" we have to first define what "working" is. It's my understanding that probiotics are harmless to humans but also kill harmful bacteria in the gut keeping the gut flora in balance. I personally don't see why you would require 1 billion+ when bacteria multiplies every 20 minutes or so and I don't see what benefit taking it daily will do if you are taking the same probiotic over and over, the first time you take the probiotic it's in you, it grows, it lives within you multiplying over and over, to continue taking the same probiotic over and over just seems a waste of money and resources.


07/11/2013 - 2:35am

I know this article is ooooold, but you never know; someone like me might find it now, and find it helpful. Good info.

Just a couple of points of clarification on the first reader comment to the article - There are actually a few reasons for high doses of probiotics.
First, we need to ensure that they reach the desired point of the gut. We have some pretty nasty natural defenses against bacteria in our bodies, and as it happens, these defenses work pretty well.
We also need to keep in mind that we aren't simply adding bacteria to the microbiota, but actively encouraging competition. When you consider that fully half (!!!) of fecal matter is bacteria (seriously, that's a disgusting statistic that's worth looking up; we are talking in the range of tens of trillions of bacteria in the gut alone), the measly 1 billion bacteria in that probiotic pill don't seem like that great a defense. On a human scale, 1 billion is a big number, but on a bacterial scale, 1 billion is barely a starter colony. Dosing these beneficial bacteria over time gives them a competitive advantage, by allowing them to survive even if they can't directly out-compete the bad bacteria. Fermented foods and, really, dirt, were such a huge part of our diets, that our bodies evolved to support changing gut flora based on foods being eaten.

It's also worth keeping in mind that as far as probiotic PILLS are concerned (which is the only place you would find a numerical value for your bacteria), the number of bacteria indicates how many were in the dose before it left the factory, NOT what you actually consume. The bacteria used in probiotics aren't the best for the job, they are just the bacteria that are stable enough to be cultured sufficiently to manufacture (most bacteria in the gut will not grow in cultures outside the gut), but even so, large numbers of those bacteria die while it sits on the shelf, especially if it wasn't always stored in temp-controlled facilities. In order to get a dose approaching a billion, you need a pill with at least double that, maybe even triple.

As for why they need to be dosed daily - as it turns out, most of the bacteria that we want in our guts don't actually colonize our bodies; they are transient, and come and go depending what we eat. Throughout the history of humanity, we have consumed large amounts of fermented foods (that was, after all, one of the only ways to preserve foods before refrigeration) and a large variety, as well. Since the bacteria present in the body change based on the diet of the person, and having bacteria which serve no function is maladaptive, those with no or limited ability to reproduce in the environment of the gut will be purged from the system. Very few of the bacteria used for fermentation (or in probiotic pills) are capable of colonizing the gut (one notable exception, indeed the only that I am aware of thusfar, is lactobacillus pylori, which can be found in various vegetable ferments as the last-stage of fermentation, and which collonizes the lower GI. L. Pylori adheres to the epithelial layer of the large intestine, and actively prevent harmful bacteria from taking hold and entering the blood. This, too, needs to be dosed semi-frequently, simply to rejuvenate the gene pool - adaptation is your best friend.)

HOWEVER. Just because bacteria only last a short time in the system, does not mean they do not have some long-term benefits; bacterial reproduction is a fascinating thing, and bacteria can actually grab up DNA fragments from their environment. This means that if you use probiotics, those gut bacteria which are more permanent are likely to acquire useful adaptations, such as the ability to use a compound that was previously wasted. This is exactly why it's a good idea to get probiotics from numerous food sources, rather than pills. Fermented foods such as kefir or kimchi have 10+ strains of live and active bacteria, and likely dozens more that have grown and died, leaving behind DNA fragments for your resident microbiome to use. This puts the single-strain probiotics, and even the multi-strain ones, to shame; the bacteria in foods are mostly alive, regardless how long it sits, there is more variety in the strains you get, and these foods are pennies compared to probiotic supplements (in fact, you can make them yourself for next to no cost, especially if you have a garden - for some ferments, you don't even need to add a starter culture, everything the ferment needs is already present on the foods, you just need to grow them sufficiently to make it past your defenses)

I hope this can be of use to someone at some point; there's so much bad info or lack of info out there about this topic, and it's one of great importance.


06/10/2015 - 6:17am

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