Probiotics

As I show in see.nf/probiotics, a recent systematic review of randomized controlled trials on probiotic supplements for healthy older adults found that health benefits were not sufficiently proven, and an analysis of hundreds of studies revealed that in many of them, harms were not reported at all, were reported inadequately, or were reported inappropriately, which undermines our confidence in the safety of such products. There are, for example, concerns about antibiotic resistance.

Probiotics are often selected specifically to be antibiotic-resistant so that they can be taken together with antibiotics and relieve diarrhea, but then the probiotics can transfer their antibiotic resistance to pathogens in the gut. The irony is that probiotics sometimes hinder rather than promote microbiome recovery after taking antibiotics, so it would be smart not only to bank an autologous blood unit before a planned surgical procedure in case you need a transfusion, but also to store your own stool samples before antibiotic therapy so you can restore your microbiome within a few days afterward.

Mislabeling and contamination of probiotic supplements

Even if a particular probiotic is proven to help, there is no guarantee that what the package says is actually in it. No probiotic preparation has FDA approval, so they are all sold under the lax rules for dietary supplements. There are products on the market that contain microorganisms such as Bacillus licheniformis, which are not even known to occur in the human digestive tract. (It is a soil microbe used to break down chicken feathers so they can be mixed into animal feed.) But what if you just reach for a probiotic that is generally considered safe and effective, such as Bifidobacteria? Good luck with that. An investigation of 16 commercial Bifidobacteria supplements found that only one of them contained the ingredients listed on the label. Even in the same product, the composition sometimes changed from batch to batch—or even from pill to pill from the same bottle.

An analysis of commercial probiotics in the United States found that many major brands—for example, GNC, Walgreens, Procter & Gamble, NaturesPlus, Nature’s Bounty, and New Chapter Organics—did not live up to the claims of their ingredient listings. Most of these products were also contaminated with microorganisms not listed on the label; in the case of a GNC product, it was mold. For most foods that allegedly contained probiotics, the labeling was also inaccurate. For example, only 2 of 25 tested “probiotic” dairy products—such as yogurt—matched what the label said. Unfortunately, quality did not improve for probiotic products. A report titled “The Unregulated Probiotic Market” explains the simple reason for this: With so little regulation, manufacturers have no incentive to label their products accurately.

The data on probiotics are said to be so heavily distorted by personal and financial interests, and so unusable due to inadequate regulation, that they “make an objective assessment nearly impossible.” Even if you manage to get the right dose of the right strain of the right probiotic, it does not seem to colonize the gut. If the gut were receptive to the good bacteria, they would presumably already be there anyway. Without dietary change that alters the ecosystem in the gut, probiotics do not take hold, so you would have to take them for life. Fecal transplants and probiotics can only be a temporary solution if we keep putting in the wrong fuel. If we do not change our diet, it is a pure waste of money to buy vegan poop on the black market (brown market?). On the other hand, we can select our own good bacteria and promote their growth if we nourish ourselves with foods rich in prebiotics—that is, simply “eat more whole plants.”

What about fermented foods?

If commercial probiotics are unreliable, what about those that naturally occur in fermented foods? I have addressed the benefits of cultured milk, in which some of the galactose, branched-chain amino acids, and microRNAs are eliminated. Beyond their effects on the aging process, fermented dairy products are less burdensome for people with lactose intolerance (the majority of humanity). Although milk and kefir hardly differ as causes of abdominal pain and diarrhea, you fart less after kefir—seven times in eight hours after consumption, compared to thirteen times after milk.

A randomized placebo-controlled double-blind study of kefir found no benefit for the prevention of diarrhea after taking antibiotics compared with a corresponding placebo sterilized by heating without living microbes. Similarly, a randomized controlled trial found that for irritable bowel syndrome, live sauerkraut offers no increased benefit over dead (pasteurized) sauerkraut. In Japan and Korea, consumption of pickled sour vegetables is associated with a higher stomach cancer risk (whereas fresh vegetables are associated with a lower risk). This is thought to be due to the salt that is added to fermented vegetables to prevent the growth of undesirable microbes. Nevertheless, in Japan, consumption of pickled vegetables is associated with lower overall mortality, though it does not perform better than fresh vegetables.

Bacillus subtilis, the bacterium used to make a fermented slimy soy food called natto, extends the life span of C. elegans. In humans, higher natto consumption and longer life are linked, though without adjusting that calculation for other dietary and lifestyle habits, so it could be more of a marker of traditional Japanese eating patterns than natto itself.

Prebiotics and postbiotics

If you look at which publications in the nutrition-science literature have been cited most frequently, the original paper on the glycemic index ranks tenth—it has been cited over 1000 times. But among the top 5 with over 2000 citations is the article “Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics.” As already explained, prebiotics are food components that feed the good gut bacteria, such as fiber and resistant starch. With every gram of fiber we eat, we produce almost 2 grams of stool because we promote bacterial growth with it. Probiotic pills may be slated as the next big source of Big Pharma billions, but why swallow a pill when you can culture your own probiotics at home? A meta-analysis of over 60 randomized controlled trials on prebiotics found that they increase the amounts of common probiotics such as Bifidobacteria and Lactobacillus.

Prebiotics do not just promote the growth of probiotics already present. They are also used by our friendly gut flora to create postbiotics—the byproducts of microbiome metabolism that benefit us. Our good bacteria eat prebiotics, such as fiber, and produce short-chain fatty acids (SCFAs), which are then absorbed from the colon into the bloodstream, circulate throughout the body, and reach the brain. These important fiber-derived SCFAs can have far-reaching effects on all kinds of things, from inflammation and immune defenses to mental health.