Funded by Solnul manufacturers MSP Starch Products Inc, the randomised, double-blind, placebo-controlled clinical trial has explored the effects of a low-resistant potato starch dose on the microbiome and related outcomes in 75 healthy adults over four weeks.
The study, conducted by nutraceutical research organisation Nutrasource, based in Canada, found that Solnul had a prebiotic effect when consumed for four weeks at a 3.5 g per day.
Clinical trials evaluating the health benefits of resistant starch (RS) fortification have previously investigated high doses in food formats, producing benefits including laxation, lower fasting blood glucose or hemoglobin A1C (HbA1c), and improved insulin metabolism.
RS is defined as the sum of starch and starch-degradation products that, on average, reach the human large intestine. Most RS is classified into five types based on the natural or manufactured form. Solnul is RS Type 2 (RS2), which is categorised as naturally occurring starch that resists amylase due to the shape of the granule.
While current research has suggested that higher doses of RS2 (15-30g per day) are needed to achieve metabolic improvements, the new study concluded that lower doses of RPS could provide a prebiotic effect by enhancing the abundance of beneficial bacteria while improving stool consistency.
Increases in Bifidobacterium and improved stool form were found to be consistent with conclusions from previous prebiotic studies, however, quantified substantial increases in Akkermansia were noted as ‘novel’.
Chief Scientific Officer of Solnul, Dr. Jason Bush, stated: “Resistant starch (RS) has been known for decades as an ingredient that can reduce glycemic impact when used to replace digestible starch in starchy foods. In these applications, the more digestible starch you replace, the greater the glycemic lowering effect.
“When researchers studying RS in these formats eventually began incorporating microbiome investigations, they found prebiotic effects, albeit at exceptionally high doses (30-50g/day). This publication demonstrates a prebiotic effect at one-tenth of those doses, meaning that Solnul can now be used at doses comparable to oligosaccharide doses (ie. Solnul @ 3.5g/day vs. Sunfiber @ 5-6g/day).”
Study and assessment
The prebiotic properties of RPS were assessed by giving 3.5 g or 7 g of resistant potato starch (RPS) per day for four weeks while measuring the relative abundance of Bifidobacterium and scores of bowel movement consistency.
Results found that the 3.5 g RPS group demonstrated significantly greater increases in the relative abundance of Bifidobacterium compared to the placebo group, along with significantly fewer bowel movements that indicated either constipation or diarrhoea. Improvements in only diarrhea-associated bowel movements were also found in the participants in the 7g RPS arm.
The study did also find that while the relative abundance of Bifidobacterium increased in response to 7g of RPS, the average increase was approximately 33% lower than what was observed in the 3.5 g arm. This was also the case when recording levels of Akkermansia.
Participants in the 3.5g RPS arm showed statistically significant increases in Akkermansia levels in comparison to the placebo group, supporting the possibility that RPS can encourage the development of microbes that are related to health.
The authors conclude: “To our knowledge, this is the first report of a low-dose fermentable fiber [Solnul] normalising stool form in a clinical study of healthy individuals.”
Mechanism of action
The understanding of how Solnul RS stimulates the growth of Akkermansia, bacteria known to feed on mucins, large, highly glycosylated proteins which are important for the luminal protection of the gastrointestinal tract, is still being investigated.
Akkermansia, including Akkermansia muciniphilia, utilises host mucus-derived glycans as an energy source. Akkermansia muciniphilia has been found in previous research to promote healthy metabolism and has been developed into probiotic and postbiotic formats.
Past clinical trials evaluating the effects of administering probiotic strains of Bifidobacterium also showed increases in Akkermansia levels, suggesting that the RPS-dependent increases could be a consequence of Bifidobacterium activities or other RPS-dependent changes in the microbial environment.
Cross-feeding between Bifidobacterium and butyrate-producing bacteria has previously been hypothesised to enhance mucin secretion, thereby increasing Akkermansia.
The authors report some limitations to the study. They state: “Bowel movement records were not kept beyond the 4-week time point, making it difficult to connect changes in bowel movement scores to changes in the composition of the gut microbiota-derived from a stool sample collected at the end of the study. A longer study would also be useful to confirm the stability of findings.
“The short duration also limited the investigation into the effects of RPS on the gut microbiota, which has pronounced beneficial effects at higher doses for longer durations.”
“Consumption of Solnul™ Resistant Potato Starch Produces a Prebiotic Effect in a Randomized, Placebo-Controlled Clinical Trial”
Authors: Jason R. Bush, Joshua Baisley, Scott V. Harding, and Michelle J. Alfa.