Prebiotic Soda and the Allure of Marginal Health Gains

Why are Americans obsessed with marginal health gains? What’s the advantage of one more point on your Oura score? Why is protein being added to almost every food product in our supermarkets?

Some people may just want to correct a deficiency. Others, we know, are passionate about living the longest, healthiest possible lives. Either way, why do so many of us assume that every little health tweak pays off?

A common answer is the “more is better” bias: If a little of something is healthy, more must be healthier. You buy that protein popcorn salt because, you assume, every gram helps.

I think this is only part of the story. For instance, in recent years we’ve heard a lot about the power of tiny interventions. I’m thinking of practices ranging from exercise snacks to microdosing psychedelic drugs. Here the takeaway is not “more is better” but rather “a little does a lot”.

This week’s newsletter was prompted by a July 25 presentation at the NUTRITION 2026 conference. The presentation focused on the content of prebiotic sodas, a product that’s become so popular even Coca-Cola and Pepsi-Co have entered the market. Mulling over this presentation, I had three questions I want to discuss here:

1. What are the health benefits of prebiotics?

2. Should anyone be drinking prebiotic sodas?

3. Why have prebiotic sodas become so popular?

In discussing the third question I’ll delve more deeply into the allure of marginal health gains.

(I know that “delve” is one of the most common signs of AI-generated text, but I used no AI for this newsletter. I refuse to let the chatbots co-opt a useful verb. Also, I really like em dashes – I started using them long before Sam Altman was born.)

What are prebiotics?

Your gut contains hundreds of trillions of microorganisms – mostly bacteria – that help keep you healthy. Energy sources for these tiny creatures include carbohydrates known as prebiotics.

Prebiotics pass through your stomach without being digested. Once they reach the colon, they may get “eaten” by microorganisms that thrive there. More precisely, the microorganisms metabolize them via fermentation.

The more familiar term “probiotics” refers to one type of living microorganism, such as Lactobacillus, that derives energy from prebiotics. Crudely speaking, probiotics eat prebiotics.

Here are a few examples of prebiotics and their natural food sources:

In Appendix A, I say more about definitional issues. The TL;DR is that by definition a prebiotic must have health benefits, and so we might ask whether that’s what the data show.

1. What are the health benefits of prebiotics?

The concept of prebiotics was first proposed in 1995, and the definition has evolved since then, so there hasn’t been much time for research on potential benefits. Even the industry-supported junk science – and there’s a lot of it – tends to describe the evidence cautiously, using terms like “potential” and “promising”.

What’s being promised? A few examples:

• Reduced risk of colorectal cancer

• Less gastrointestinal damage from cancer treatments

• Lower LDL cholesterol levels

• Greater insulin sensitivity and glucose regulation

• Better calcium absorption

• Enhanced treatment of gastrointestinal disorders

• Improved bowel function

In my opinion the evidence for most of these claims doesn’t even rise to the level of “promising”. This makes me very cranky.

It’s fine if you claim that prebiotics improve calcium absorption but the evidence is mixed. If you’re wrong, public health won’t be affected much.

It’s not fine to talk about cancer prevention and treatment if the evidence can’t be called promising.

Why not? Because the hucksters and social media influencers of the world may get wind of it, and if they do the public may end up being misled. Colorectal cancer rates are skyrocketing, particularly among people under 50. We shouldn’t be creating false hopes.

A few words on my skepticism before moving on.

The main reason we shouldn’t assume that prebiotics reduce the risk of cancer (or aid in its treatment) is that this isn’t what the studies show.

Often, the “evidence” is merely data showing that prebiotics improve some aspect of gut health. That’s good news but, inferentially speaking, it tends to be a long way from evidence for a reduction in cancer risk. At most it’s a hint that prebiotics could be indirectly helpful.

Meanwhile the direct evidence isn’t very direct, because the data comes from rodent models that poorly simulate cancer progression and treatment. In Appendix B I describe one of these studies.

The few observational studies on humans show no consistent associations between prebiotics and colorectal cancer risk. In fact, the main takeaway from the current literature seems to be that prebiotics may simply help improve bowel functioning – in particular, constipation.

This is good news, though it doesn’t show that prebiotics are special.

To illustrate, consider a 2022 RCT showing that folks who took a galacto-oligosaccharide (GOS) prebiotic enjoyed more relief from constipation than the control group did. Since GOSs are a kind of soluble fiber, the study merely reiterates something we know already: Increasing fiber intake can help you poop.

Are GOSs especially effective at doing so? We can’t tell, because the control group in this study received maltodextrin, a carb that wouldn’t be expected to help. Research like this doesn’t tell us how well prebiotics would fare in comparison with prunes, high-fiber cereal, or anything else known to alleviate constipation.

In sum, prebiotics nurture gut microorganisms and alter the composition of the gut microbiota, but it’s not clear that they benefit our health in any distinctive way. The prebiotics that happen to be soluble fiber are healthful because…they’re fiber.

2. Should anyone be drinking prebiotic sodas?

The prebiotic soda industry got underway in 2018 with the introduction of OLIPOP (a portmanteau of “oligosaccharide” and “pop”). OLIPOP and Poppi are industry leaders, but last year Coca-Cola and Pepsi also entered the game. (Coca-Cola manufactures Simply Pop.)

Not surprisingly (assuming you have a cynical take on Big Soda), Coca-Cola and Pepsi-Co have each taken the minimalist approach of simply fortifying their products with 3 or 6 grams of soluble corn fiber.

In contrast, OLIPOP products either contain 6 grams of cassava root, acacia, and guar fiber, or 9 grams of cassava root fiber as well as chicory root and Jerusalem artichoke inulin.

These ingredients have been shown to have prebiotic effects. However, there’s no clear evidence that any of them would improve your health, unless you’re hoping to benefit from the fiber content.

So, should you rely on prebiotic sodas for fiber?

I wouldn’t. The July 25th conference presentation that inspired this newsletter, co-authored by Carlos Díaz and Lindsey Smith Taillie at UNC Chapel Hill, analyzed the contents of 108 different prebiotic sodas. Here are what I consider the three most notable findings:

1. Most prebiotic sodas contain meaningful amounts of fiber.

Median fiber content was about 5 grams per 12 ounces of soda. To put that number in context, one of the most influential recommendations is a daily intake of 14 grams of fiber per 1,000 calories. So, at first glance, the fiber content of prebiotic sodas seems like a plus.

2. Prebiotic sodas tend to have fewer calories and added sugars than regular sodas and fruit drinks do.

Another plus, although saying that something is healthier than a Coke or an artificially-sweetened fruit punch isn’t saying much.

3. Prebiotic sodas tend to have more calories and added sugars than diet sodas and flavored sparkling waters.

Not a plus, but still, prebiotic sodas do contain fiber. Doesn’t that make them worth drinking?

I’d say no. Dietary fibers differ in their effects on digestive function. Inulin would be more effective at alleviating mild constipation than soluble corn fiber would, but the latter may promote calcium absorption. When you eat whole foods, you enjoy the benefits of a variety of fibers, not to mention a full spectrum of nutrients. If you drink prebiotic soda, you only benefit from one or a few types of fiber, and perhaps little else.

I’m not arguing that prebiotic additives or supplements are never worthwhile. If I had mild constipation, I’d consider inulin or psyllium husk supplements – assuming I’d been eating a healthy, plant-based diet, staying hydrated, and getting enough exercise. I might even consider these supplements as pat of a broader strategy for lowering LDL cholesterol. But I wouldn’t rely on prebiotic sodas for any of this.

3. Why have prebiotic sodas become so popular?

The market for prebiotic sodas is expected to grow, at least through 2030, owing mainly to interest among younger and/or health-conscious consumers. As a Coca-Cola executive noted last February

We found that consumers, especially the wellness-focused Gen Z-ers and Millennials, were really interested in...prebiotic sodas.”

This brings me back to my earlier question: What makes these products so appealing?

For roughly two decades, gut health has played an important and often faddish role in public consciousness. Manufacturers leverage this trend via slick marketing that folds in vague statements about the healthfulness of prebiotic sodas. (FDA restrictions necessitate vagueness.) For instance, Coca-Cola’s Simply Pop ads note that its 6 grams of prebiotic fiber “supports gut health”.

This is true, but only in the way that the zinc and vitamin C in Simply Pop also “supports immune health”. Lots of things “support“ gut and immune health. Water, for instance. Exercise. A good night’s sleep. Et cetera.

These products have no distinctive health benefits, though the manufacturers would like you to believe otherwise. We have no guidelines for daily prebiotic intake, but the companies tell you exactly how many grams each can of soda contains. Presumably this taps into the “more is better” and “a little does a lot” biases. I don’t know how much soluble corn fiber I need today, but surely 6 grams is better than 3...

Wherever possible, soda manufacturers also try to leverage the science. For instance, an OLIPOP web page updated this July 23 proclaims the following:

“We also ran an at-home human clinical pilot study comparing OLIPOP Vintage Cola to a traditional cola. The results? OLIPOP showed a better-for-you blood sugar response both on its own and paired with a carb-rich meal. That’s science doing what it does best: Reinforcing what our taste buds already knew.”

I beg to differ. Science at its best does not simply pair two colas and say that one produces a better blood sugar response. If you want a better blood sugar response you don’t drink sugar-sweetened cola in the first place.

Also, this was a terrible study. An OLIPOP product with 3 grams of sugar was compared to a “traditional” soda with 39 grams of sugar.

OLIPOP’s results say, in effect, that hitting yourself with a tiny hammer won’t hurt as much as hitting yourself with a large one. (I had no idea.)

Here’s what I’ve suggested so far: Prebiotic sodas have become popular owing to a society-wide interest in gut health that’s intensified by slick marketing, all of which activate “more is better” and “a little is a lot” heuristics. Even if a consumer is aware that a particular soda doesn’t contain much prebiotic fiber, and even if they don’t know how much they need, the fact that it contains a little is assumed to be beneficial.

(I can’t speak for consumer impressions, but I suspect that prebiotic sodas appeal to some people because they mistake “prebiotic” for “probiotic”, or because the term “prebiotic” sounds science-y, even if it’s not understood.)

I see two other psychological forces at play here.

One is the sort of reframing that Nobel Prize-winner Daniel Kahneman discussed throughout his career (see, for instance, his 2011 book “Thinking Fast and Slow”). When faced with a difficult question, we tend to unconsciously simplify. If we’re concerned about our fiber intake, we don’t ask “what are the pros and cons of drinking this prebiotic soda?” Rather, we ask “does it contain fiber?”

Kahneman didn’t claim that we’re unable to reason in analytical, nuanced ways. Rather, his point was that our default – what he calls System 1 thinking – includes rapid, mostly unconscious simplifications.

From an industry perspective, this is a gift, because it suggests that people who are seeking more fiber will see the ad mentioning 6 grams of prebiotic fiber and immediately think, oh, here’s a good way to get more.

Finally, there may be halo effects, which can also be traced back to System 1 thinking.

A halo effect occurs when a positive impression of one feature of a person or thing leads people to assume that other, unrelated features of that person or thing are positive. In the case of prebiotic sodas, if you view prebiotic fiber favorably, noticing that a particular can of soda contains some will make the entire product seem appealing, leading you to ignore less positive features such as sugar content.

In sum, a confluence of social trends, marketing, science, media, and psychology seems to be driving interest in prebiotic sodas. More broadly, I think this is just one example of the forces underlying the American obsession with incremental health gains. Prebiotic sodas may be growing in popularity for much the same reasons that protein candy or protein Pop-Tarts are.

If you live a healthy lifestyle and keep your added sugar intake low, prebiotic sodas are probably harmless (unless you’re drinking several per day). But I don’t see any distinctive benefits, unless the point is to switch from traditional sodas to something containing less sugar.

I had hoped to arrive at a more positive conclusion. My apologies. OLIPOP sells Barbie Peaches & Cream prebiotic soda. That’s fun at least. (Or maybe creepy?)

Thanks for reading!

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Appendix A: More on the definition of “prebiotics”

I would like to tell you that a prebiotic is an objectively defined thing, like a carbohydrate or a bacterium, but the truth is more complicated – and problematic.

The most influential definition, updated by the International Scientific Association for Probiotics and Prebiotics in 2017, is that a prebiotic is

“a substrate that is selectively utilized by host microorganisms conferring a health benefit”

The first part of this definition is tricky but manageable. Some compounds, like inulin, clearly meet the criteria, but scientists are still debating whether others, such as polyphenols and psyllium, are “selectively utilized” by gut microorganisms. Meanwhile “substrate” allows a prebiotic to be just about anything, not necessarily a carbohydrate, and the definition allows for utilization to take place outside the digestive tract.

Reference to a “health benefit” makes the definition a little squishy. Prebiotics do nourish and alter the gut microbiota, and they increase production of gut-supportive compounds such as short-chain fatty acids (SCFAs). But lots of foods, including non-prebiotic fruits and vegetables, offer such benefits too. It’s not clear what, if anything, distinguishes the health impacts of prebiotics. All we can say for sure is that those prebiotics which are dietary fiber have known fiber-related benefits.

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Appendix B: Animal models of prebiotics and cancer risk

Typical of the studies suggesting that prebiotics reduce cancer risk is a 2001 RCT in which rats spent three weeks eating either non-prebiotics or one of two chicory-based prebiotic diets. The rats were then exposed to a carcinogen. 24 hours later, autopsies revealed that the rats who’d been eating prebiotics experienced more apoptosis, or cell death.

In theory, what happened is that the prebiotics spurred a protective response to the carcinogen. But it’s not clear whether that response would last long enough to be useful, and the prebiotics may have killed cells the carcinogen would never affect. In any case, we have no idea whether human bodies would show a similar response.

Exacerbating the dearth of human studies is an annoying tendency for some experts to gloss over or unintentionally hide the extent to which the data has been obtained from animals. For instance, consider this summary statement from an otherwise quite balanced 2024 review:

The syntax of the first sentence implies that studies with humans have demonstrated all of the benefits mentioned. In fact, every one of the more than a dozen studies referred to here, except for one on mucosal inflammation, was conducted in vitro or with rats or mice.

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