A $1 synbiotic cut sepsis in Indian newborns, and adult products haven’t matched it

Key takeaways

• A synbiotic, as defined by an international expert panel in 2020, is a mix of live microbes and a food for microbes that has been shown to help as a combination¹³.
• In a 2017 trial of 4,556 healthy newborns in rural India, a week of a synbiotic cut sepsis or death in the first two months from 9% to 5.4%, at about $1 a baby⁴⁵.
• In adults, pooled studies show small changes, such as about 1.3 kilograms of weight loss and a 2.8 mg/dL drop in LDL cholesterol, and too few trials to judge IBS⁹¹⁰¹².
• A 2022 review found that most commercial synbiotics simply add a prebiotic to a probiotic, often at doses below what’s expected to help¹³.
• Yogurt with raw garlic, or live sauerkraut beside a chilled potato salad, pairs live cultures with prebiotic foods, but we found no trial testing whether such pairings work as synbiotics³.

In 149 villages in the Indian state of Odisha, researchers gave newborns a daily dose by mouth for one week, starting when they were 2 to 4 days old⁴. Half got a placebo. The other half got a bacterium, Lactobacillus plantarum, plus 150 milligrams of fructo-oligosaccharide (FOS), a sugar compound that feeds microbes⁴⁵.

Over the babies’ first two months, 9% of the placebo group developed sepsis, a life-threatening reaction to infection, or died⁵⁶. In the treated group, it was 5.4%⁵⁶. The researchers stopped the study early, with about half the planned babies enrolled, because the synbiotic was doing far better than the team had predicted⁴.

A week’s supply cost about $1 per baby⁴.

That combination is called a synbiotic: live microbes packaged with food meant for them. The 2017 study, published in the journal Nature, is still the best-known evidence that the idea can work.

Now walk down an American supplement aisle. You’ll find “synbiotic” capsules and powders aimed at healthy adults.

In a national survey, more than 1% of U.S. adults and children reported taking a synbiotic supplement¹³. For those buyers, the evidence looks very different.

A synbiotic is a partnership that has to be tested as a pair

In 2019, a panel convened by the International Scientific Association for Probiotics and Prebiotics (ISAPP) met to pin down the word¹. Their 2020 definition calls a synbiotic “a mixture comprising live microorganisms and substrate(s) selectively used by host microorganisms,” one that benefits the person taking it¹.

“Substrate” means food for microbes. The microbes that eat it can be the ones in the product or the ones already living in your gut¹.

The panel named two kinds:

• Complementary. A proven probiotic is mixed with a proven prebiotic that feeds your own resident microbes. Each part must meet its own standard, and the combination must show a health benefit¹.
• Synergistic. The food is chosen for the microbe in the same product. Neither part has to qualify on its own, but one study must show the microbe uses that food and that the mix helps¹.

The key rule is the same for both: the benefit has to be shown for the product as a whole, not just for each part³.

Kelly Swanson of the University of Illinois, who led the panel, put it bluntly: “We don’t want companies just randomly throwing things together”². By ISAPP’s tally, nearly 200 clinical studies of synbiotics had been published in the previous decade¹. Being studied, though, isn’t the same as being proven.

What the Odisha trial did, and didn’t, show

Pinaki Panigrahi led the trial, which was supported by the National Institutes of Health’s child health institute⁴. What it tested:

• Who: 4,556 healthy, breastfed newborns, each weighing at least 2,000 grams (about 4.4 pounds) and born at 35 weeks or later⁵.
• What: One strain, L. plantarum ATCC 202195, at 1 billion colony-forming units (a lab count of live cells), plus 150 milligrams of FOS⁵.
• Main result: Sepsis or death fell by about 40%⁴⁶. Counting sepsis alone, cases fell from 8.9% to 5.1%⁴.
• Bonus finding: Lung and airway infections that needed antibiotics fell from 6.1% to 4%⁴. Babies on the synbiotic also gained more weight by 60 days⁴.

Read the death numbers closely. There were 4 deaths in the placebo group and 6 in the synbiotic group, too few to say anything either way⁴⁶. The drop came from fewer infections, not from fewer deaths.

The trial also compared the synbiotic only with a placebo. By design, it can’t tell whether the FOS added anything to the bacterium alone.

Panigrahi himself said the result needed to be repeated in other countries and conditions⁴. He also noted that his team’s close supervision and careful follow-up won’t exist in everyday life⁴.

A newer trial points the same way, without the fiber. A larger Indian study called ProSPoNS randomly assigned 6,144 low-birth-weight babies to an eight-strain probiotic or a placebo⁷⁸. It was a probiotic only, with no added prebiotic⁸. On its website, INCLEN Trust, the Indian research group behind the trial, reports possible serious bacterial infections in 4.66% of the probiotic group and 6.17% of the placebo group⁷. Those figures come from the group itself; we couldn’t find them in a peer-reviewed journal as of October 2026.

Neither trial tells you much about babies in American hospitals or homes. Our probiotics article explains the FDA’s 2023 warnings about probiotics for premature babies. If you’re thinking about any microbe product for a baby, ask your pediatrician first.

In adults, the trials are small and the gains are modest

IBS. A 2014 review by Ford and colleagues found synbiotic data for irritable bowel syndrome too sparse to judge⁹. A 2018 review by Ford’s team said the same¹⁰.

Constipation. The 2014 review had better news for chronic constipation. Synbiotics lowered the risk of not responding to treatment by about 22%, though the authors still called the overall picture for constipation uncertain⁹.

Weight and cholesterol. A 2023 umbrella review, a study of earlier reviews, pooled 17 meta-analyses covering about 7,800 people¹². Synbiotics trimmed body weight by about 1.3 kilograms, roughly 3 pounds, and LDL cholesterol by about 2.8 mg/dL¹². HDL, the “good” cholesterol, didn’t change¹².

Those effects are small, and the studies disagreed with each other a lot¹². The authors rated the certainty as moderate or low, and they found signs of small-study bias in two results¹². Seven of the 17 reviews they pooled came from a single country, Iran, as did the authors themselves¹².

Fatty liver. A 2025 network meta-analysis compared gut-targeted treatments for nonalcoholic fatty liver disease across 37 trials¹¹. In 10 synbiotic trials, liver enzymes fell, and so did scan-based measures of liver stiffness and fat¹¹. The authors described synbiotics as possibly promising¹¹. These trials measured blood tests and scans, not long-term outcomes such as cirrhosis¹¹.

One trial cuts the other way. In a 2020 trial by Scorletti and colleagues, a synbiotic with 8 grams of FOS didn’t improve markers of liver disease¹³.

Does the pair beat the probiotic alone? That’s the whole premise, and it has barely been tested. In a 2022 trial in malnourished infants, a synbiotic did no better than its microbe alone¹³. In another 2022 trial, adding 1 gram of GOS, a prebiotic, weakened a probiotic’s effect on constipation¹³.

Claim	Evidence rating	Why
A synbiotic prevents sepsis in healthy, breastfed newborns in rural India	Promising but early	One large, well-run trial; not yet repeated46
Synbiotics help chronic constipation	Promising but early	Pooled trials in a 2014 review9
Synbiotics trim weight and cholesterol	Promising but early	Consistent but small effects; studies vary widely12
Synbiotics improve fatty liver	Promising but early	Liver tests and scans improve in small trials; one null trial1113
Synbiotics ease IBS	Not enough evidence	Too few trials to judge910
A synbiotic works better than its probiotic alone	Not enough evidence	Few head-to-head tests; two found no added benefit13
Pairing fermented and prebiotic foods acts as a synbiotic	Not enough evidence	No trials found3

Most products are a probiotic with a sprinkle of fiber

In 2022, Robert Hutkins and two colleagues took stock of synbiotics¹³. Most products on shelves and in trials, they found, are the complementary kind: a probiotic plus a prebiotic, sold together. Relatively few have been tested for true synergy¹³.

Dose worried them more. Judging by the amounts printed on labels, many products carry too little prebiotic to do much¹³. And often nobody explains why a particular microbe was matched with a particular fiber¹³.

The recent trials the review listed used anywhere from 1 gram to 60 grams of microbe food¹³. A label listing a fraction of a gram falls below every dose in that set.

Labels can also overstate what’s inside. When ConsumerLab, a private testing company, checked five prebiotic supplements in 2022, actual prebiotic fiber ranged from 26% to 96% of the listed ingredient amount¹⁵.

Who’s minding the store? In the U.S., synbiotic capsules and powders are sold as dietary supplements. In 2010 testimony to the Senate, the FDA’s principal deputy commissioner laid out the rules under the 1994 Dietary Supplement Health and Education Act. The FDA doesn’t approve supplements before they reach consumers, he said, and makers are responsible for safety and for the truth of their claims¹⁴.

Under that law, a claim about supporting a body function, such as “supports digestive health,” isn’t pre-approved by the FDA¹⁴. The label must say the FDA hasn’t evaluated the claim, and the company must notify the agency within 30 days of marketing¹⁴. Our article on why labels say “supports” and never “cures” explains what those claims can and can’t promise.

What you pay for the “syn”

Price the parts separately, and a synbiotic’s markup becomes easier to judge.

In 2022, ConsumerLab found prebiotic supplements cost 12 to 85 cents per gram of prebiotic fiber¹⁵. By our math, matching the 8 grams of FOS in the 2020 liver trial¹³ would cost about 96 cents to $6.80 a day from a powder.

A capsule with a pinch of inulin doesn’t come close to that dose. So if a synbiotic costs much more than the same probiotic sold alone, much of the difference may be paying for an ingredient at a dose too small to be expected to help¹³.

A quick cost check:

• Write down the daily cost of the synbiotic.
• Find the same probiotic strain sold alone, and note its daily cost.
• Look at the prebiotic grams per serving on each label.
• If the synbiotic’s prebiotic dose is tiny, compare it with eating prebiotic foods, which add fiber and nutrients for the price of groceries.

For the Indian newborns, the whole week cost about $1⁴. The lesson there isn’t that synbiotics must be cheap. It’s that a tested, specific product can be.

The kitchen version: pairing live cultures with prebiotic foods

Natural-health cooks have long combined foods that seem to belong together. The synbiotic idea gives that habit a scientific frame, but only part of it has been tested.

What’s established: Some fermented foods carry live microbes, though not all do³. Onions, garlic and Jerusalem artichokes contain inulin and FOS, and potatoes that are cooked and then cooled contain resistant starch, all of which feed gut microbes³.

What’s theory: That eating them together works better than eating them on separate occasions. ISAPP’s rule says the benefit must be shown for the combination³. We found no trial of these home pairings.

That still leaves plenty of good food. These pairings are our own suggestions:

• Plain yogurt with grated raw garlic, as a dip or sauce for vegetables.
• Kefir blended with a little cooked, cooled potato in a cold soup.
• Refrigerated live-culture sauerkraut beside a chilled potato salad made with onions.
• Yogurt dressing over roasted Jerusalem artichokes, added after cooking so heat doesn’t kill the cultures.
• Raw onion folded into a yogurt-based salad dressing.

Start small. Too much prebiotic food at once can cause gas or bloating, ISAPP notes³. If you have IBS, read our prebiotic foods article first, since several of these foods can set off symptoms. Our fermented foods article explains which jars still hold live cultures.

Questions readers ask

The bottom line

The synbiotic idea is elegant: give helpful microbes their preferred food so they’re more likely to thrive. In one large trial in rural India, a week of a cheap, specific synbiotic cut infections in healthy newborns. That result hasn’t been repeated, and it doesn’t tell us whether the fiber mattered.

For adults, the evidence is thinner. Pooled studies show small changes in weight, cholesterol and liver tests, too little data exists for IBS, and the few tests of whether the pair beats the probiotic alone haven’t favored the pair. Before you pay extra, ask whether the combination was tested as a whole, or build a pairing on your plate for the price of groceries.

Related reading

• A prebiotic soda has 2 grams of fiber, and half an onion may have more
• Six servings of fermented food a day reshaped gut microbes in a Stanford trial, so start with one
• Why supplement labels say ‘supports’ and never say ‘cures’
• The supplement math that changes which bottle wins
• Probiotics work for a few jobs, so match the strain or skip the bottle

Sources

1. Scott K, Sanders ME, Swanson K, Gibson G, Hutkins B. “New Synbiotic Definition Lays the Groundwork for Continued Scientific Progress” (on Swanson KS, Gibson GR, Hutkins R, et al., “The ISAPP Consensus Statement on the Definition and Scope of Synbiotics,” Nature Reviews Gastroenterology & Hepatology, 2020;17:687–701). ISAPP, August 21, 2020, updated June 21, 2025. isappscience.org
2. Quinn L. “Global Gut Health Experts Guide Growth of Synbiotics.” University of Illinois College of Agricultural, Consumer and Environmental Sciences, August 24, 2020. aces.illinois.edu
3. International Scientific Association for Probiotics and Prebiotics. “Biotics” consumer and educational materials (probiotics, prebiotics, synbiotics). ISAPP, 2019–2024.
4. Wein H. “Probiotic Prevents Infant Infections in Rural India.” National Institutes of Health, August 29, 2017.
5. Gut Microbiota for Health. “Large Clinical Trial in India Finds Synbiotic May Help Prevent Neonatal Sepsis.” European Society of Neurogastroenterology & Motility, October 19, 2017. gutmicrobiotaforhealth.com
6. Panigrahi P, et al. “Data From: A Randomized Synbiotic Trial to Prevent Sepsis Among Infants in Rural India” (abstract of the 2017 Nature paper). Dryad. datadryad.org
7. INCLEN Trust International. “ProSPoNS: Probiotic Supplementation for Prevention of Neonatal Sepsis” (study page). Accessed October 2026. inclentrust.org
8. Trials (BioMed Central). “Evaluating the Efficacy of a Multistrain Probiotic Supplementation for Prevention of Neonatal Sepsis in 0–2-Month-Old Low Birth Weight Infants in India: The ProSPoNS Study Protocol.” Trials, 2021;22:242. trialsjournal.biomedcentral.com
9. Ford AC, Quigley EMM, Lacy BE, et al. “Efficacy of Prebiotics, Probiotics, and Synbiotics in Irritable Bowel Syndrome and Chronic Idiopathic Constipation: Systematic Review and Meta-Analysis.” American Journal of Gastroenterology, 2014;109(10):1547–1561 (McMaster University record). experts.mcmaster.ca
10. Ford AC, Harris LA, Lacy BE, Quigley EMM, Moayyedi P. “Systematic Review With Meta-Analysis: The Efficacy of Prebiotics, Probiotics, Synbiotics and Antibiotics in Irritable Bowel Syndrome.” Alimentary Pharmacology & Therapeutics, 2018;48(10):1044–1060 (Houston Methodist record). scholars.houstonmethodist.org
11. Song Y, Liu S, Zhang L, Zhao W, Qin Y, Liu M. “The Effect of Gut Microbiome-Targeted Therapies in Nonalcoholic Fatty Liver Disease: A Systematic Review and Network Meta-Analysis.” Frontiers in Nutrition, 2025;11 (DOAJ record). pubmed.ncbi.nlm.nih.gov
12. Musazadeh V, Mohammadi Anilou M, Vajdi M, et al. “Effects of Synbiotics Supplementation on Anthropometric and Lipid Profile Parameters: Finding From an Umbrella Meta-Analysis.” Frontiers in Nutrition, 2023;10:1121541. frontiersin.org
13. Gomez Quintero DF, Kok CR, Hutkins R. “The Future of Synbiotics: Rational Formulation and Design.” Frontiers in Microbiology, 2022;13:919725. frontiersin.org
14. Sharfstein JM. Testimony of the U.S. Food and Drug Administration before the U.S. Senate Special Committee on Aging. May 26, 2010. aging.senate.gov
15. ConsumerLab.com. “Prebiotic Supplements” test results news release. October 28, 2022. consumerlab.com