Speaking to NutraIngredients at SupplySide Global 2026, Jason Bush, chief scientific officer at Soulful, said the industry had little incentive to revisit established findings when additional studies could open the door to new claims.
“I think there’s a kind of a natural attraction to do adjacent studies,” he said. “So you do your kind of foundational study, and then you want to kind of expand your claims...[but] it’s risky to try to reproduce your studies.”
The company recently put that approach to the test with a replication trial of its Solnul resistant potato starch ingredient, reproducing some earlier findings while failing to confirm others.
Repeating the research
The four-week randomized, double-blind, placebo-controlled trial, published in Nutrients, investigated whether 3.5 g of Solnul daily could reproduce previously reported effects on gut bacteria and stool form in healthy adults.
The 74-participant trial found a greater increase in Bifidobacterium compared with placebo in the per-protocol analysis, although the difference was not significant when researchers included the broader analysis population.
Participants taking Solnul also recorded a higher proportion of normal stools, classified as Types 3 and 4 on the Bristol Stool Form Scale.
The findings were less consistent for Akkermansia. While levels increased from baseline in the Solnul group, the difference compared with placebo was not statistically significant, meaning the trial did not meet its primary endpoint.
Bush said the findings reflected a persistent challenge in microbiome research: Individual responses remain difficult to predict.
“I think that the heterogeneity in the microbiome is going to make it really tough to consistently reproduce effects,” he said. “And I think just at a basic level, the science isn’t really there around the microbiome to really understand why some studies succeed in reproducing effects and other ones fail.”
He also noted that advances in microbiome analysis since the original trial had allowed researchers to identify more bacterial taxa, complicating comparisons between the two studies.
Several placebo participants showed unexpectedly large increases in Akkermansia, he added, noting there was no evidence to dismiss the observations as technical errors.
A closer look at tolerability
One finding Bush considered particularly important was the ingredient’s consistent gastrointestinal tolerability.
“I guess the final thing that I think was maybe the most important figure in this whole manuscript...is the tolerability angle,” he said.
The trial reported no significant differences in gastrointestinal symptom scores between Solnul and placebo, and no serious adverse events.
The researchers also added measures of bowel movement frequency and days without a bowel movement, neither of which the earlier trial had assessed.
Participants taking Solnul recorded more bowel movements than they had before supplementation, but the change was not significantly different from placebo. The reduction in days without a bowel movement, however, was significantly greater in the Solnul group.
“We didn’t really look at laxation claims in the first study, but we did in the second study,” Bush said.
Asked why the company had added these measures, he noted: “We’ve just been in the market long enough now that we know that’s an important thing.”
What should brands expect?
The International Scientific Association for Probiotics and Prebiotics (ISAPP) identifies confirmatory trials as an additional step in building evidence for prebiotic efficacy, according to the study manuscript.
But Bush was reluctant to suggest that a single positive trial should no longer be enough to support an ingredient claim.
“I don’t think we’re there yet,” he said.
He argued that brands with greater retail exposure may have more reason to demand replicated evidence, particularly when their product claims face closer scrutiny.
“And I think duplicating, replicating a study gives them that confidence,” he said.
For suppliers working with a more limited evidence base, Bush advocated further clinical investment without insisting that every subsequent trial follow the original protocol.
He also saw value in unsuccessful replication attempts, which could expose weaknesses in study design, compliance or delivery formats.
“I think every time we do a good study, we learn something,” he said.
Source: Nutrients 2026, 18, 3538. doi: 10.3390/nu18213538. “Examining the Gastrointestinal Effects of Solnul, a Prebiotic Resistant Potato Starch: A Replication Randomized, Double-Blind, Placebo-Controlled Clinical Trial in Healthy Adults”. Authors: Bush, J.R. et al.
