Probiotics are all the rage. But a recent article in the Wall Street Journal, Those Probiotics May Actually Be Hurting Your ‘Gut Health’, drove home a point I often try to make about these supplements.

Probiotics contain live, microscopic organisms. Yogurt, Kefir, Kimchi, Sauerkraut, and other fermented foods have live bacterial and yeast strains. The type of microorganisms vary by brand. Prebiotics (e.g., psyllium or inulin) contain no live organisms. Instead, they are substances that humans cannot digest. The substances instead feed the beneficial bacteria of our gut.

Certain conditions, including atopic dermatitis, travelers diarrhea, and irritable bowel, may improve with the administration of specific probiotics. Probiotic formulations vary widely both in the types of organisms included and in the quantity of bacteria per dose.

Functionally, what differentiates probiotic pills from food is the QUANTITY of live bacteria that make it to the intestine. Only a few of the millions of bacteria in food make it past the harsh environment of the stomach. For example, a single serving of non-pasteurized yogurt contains approximately 200 million to 2 billion live organisms. Only a small portion of those bacteria make it to the small intestine. Interestingly, the bacterial breakdown products appear to play their own role in gut health. In contrast, a single probiotic pill usually contains 1 billion to 50 billion organisms. If the pill is enteric-coated, the entire bacterial load will make it past the stomach into the intestine.

In my opinion, we need to be cautious about indiscriminate and/or long-term use of probiotics.

Here’s my reasoning:

• First, probiotics are unregulated. Thus, you can’t be sure you’re getting the bacteria you expect; the dose you expect or if your probiotic is free from contaminants.
• Second, we are still in the early days of unraveling the role of the microbiome in health and disease. We already know half the bacteria of the gut are metabolically active. These bacteria churn out everything from enzymes to neurotransmitters. We are still mostly in the dark when it comes to which strains of bacteria are beneficial (or harmful) and how they exert their effects. We also have little idea what the short and long-term effects of different strains of bacteria might be. Delivering extreme numbers of bacteria into the intestine very likely produces unintended consequences. These consequences may be as simple as crowding out essential bacteria or may have wider systemic effects.

I have a personal story that drives home the point about unintended consequences. For several months, I was taking an enteric-coated probiotic. I noticed a linear increase in my weight, without changing what I ate or how much I exercised. Being curious about this effect, I looked in the literature. I found this interesting warning in Nature, and this meta-analysis linking Lactobacillus to weight gain. It turns out, manipulation of the gut microbiome has been used in agriculture for more than 50 years. Administration of certain strains of high-dose Lactobacillus and Bifidobacterium (the same bacteria found in over-the-counter probiotic formulations) is commonly used in the production of poultry, beef, and pork. Certain microbial strains increase the size and weight of young animals. The use of antibiotics for growth promotion is also at least partially mediated through the microbiome as I wrote in the Huffington Post.

Obesity is a single example of how the over-exuberant administration of probiotics may have unintended consequences. Given the emerging understanding of the wide-spread role of the microbiome on health and disease, there are likely more consequences to be discovered. We simply don’t know enough.

The next time you read about probiotics being the miracle cure for a medical condition, beware. The best way to obtain your bacteria is from food.

I’ll talk about prebiotics in a future entry. If you’d like to learn more about probiotics and health, see the NIH Office of Dietary Supplements (Probiotics professional fact sheet, Probiotics consumer fact sheet).