Benefits
Bifidobacterium and Akkermansia in the gut
In 72 healthy adults, 3.5 g a day for 4 weeks raised the share of Bifidobacterium in stool, the trial's main outcome, and of Akkermansia more than digestible corn starch, after outliers were removed. At 7 g a day neither rise reached significance. The trial was small, lasted 4 weeks and was funded by the maker.
Bifidobacteria and butyrate at 30 g a day
In a 12-week trial of the maker's earlier resistant potato starch at 30 g a day, Bifidobacterium rose more than on corn starch in 42 adults over 70 and in 42 adults aged 30 to 50, and stool butyrate rose slightly in the older group. These are microbiome markers; bowel movement counts did not change.
Stool form in healthy adults
In the 4-week trial, hard or lumpy stools and watery stools were less frequent on 3.5 g than on placebo among each person's last seven bowel movements, a secondary result counted per bowel movement rather than per person. Mushy or watery stools combined did not differ, 7 g did not reduce hard stools, and gut symptom scores did not change.
Fasting blood sugar and insulin in older adults
In adults over 70 without diagnosed diabetes, 30 g a day for 12 weeks lowered fasting glucose (median 5.8 to 5.5 mmol/L), fasting insulin and HOMA-IR compared with corn starch, while a second insulin resistance score did not change. Adults aged 30 to 50 showed no change. These are fasting markers, not a glucose tolerance test.
Blood fats, vitamins and choline in follow-up analyses
Post hoc analyses of the 4-week trial, led by a maker employee, reported lower serum free fatty acids, some bile acids and histamine, and higher retinol, vitamin E (alpha-tocopherol) and choline on 3.5 g a day, with no change in TMAO. In the 30 g trial, LDL cholesterol did not change overall compared with placebo.
Mechanism of action
Fermentation in the colon
The raw starch granules are not broken down by digestive enzymes in the small intestine, so they reach the colon, where bacteria such as Bifidobacterium ferment them into short-chain fatty acids including butyrate. Stool butyrate rose slightly in older adults on 30 g a day; the 4-week trial registered stool short-chain fatty acids as an outcome, but its published papers do not report them.
Responses depend on a person's gut bacteria
In the 4-week trial, Bifidobacterium and Akkermansia changes varied widely and several outliers were removed before analysis. In a study of another raw potato starch, 6 of 20 adults had no butyrate rise and no increase in the bacteria that break down resistant starch, so some people may respond little.
Proposed metabolic routes not yet tested
The trial authors suggested that fermentation products or gut hormones could explain the lower fasting glucose in older adults and the lower free fatty acids at 3.5 g a day. Neither trial measured gut hormones, and the fatty acid and vitamin findings come from post hoc analyses, so these routes remain unconfirmed in people.
Clinical trials
Randomized, double-blind, placebo-controlled three-arm parallel trial; 7 g Solnul, 3.5 g Solnul plus 3.5 g digestible corn starch, or 7 g digestible corn starch (Amioca) each morning for 4 weeks; registered NCT05242913 about two years after the trial ended; funded by MSP Starch Products, which employs the first author, with the trial run under contract by Nutrasource and two authors former maker consultants; five follow-up papers (2023 to 2025), one not indexed in PubMed, come from this trial (Bush et al. 2023, Nutrients)
75 healthy adults aged 18 to 69 with a BMI of 18 to 34.9 were randomized, 25 per arm, and 72 were analyzed (average age about 38, 69 percent women). People with IBS or other digestive disorders were excluded.
Primary outcome: Bifidobacterium rose more on 3.5 g than on placebo (p = 0.038) after outliers were removed, but not on 7 g (p = 0.14). Akkermansia rose more on 3.5 g (p = 0.014) but not on 7 g (p = 0.056). Among the last seven bowel movements per person, type 1 or 2 stools were fewer on 3.5 g (9 versus 23 of 168, p = 0.0085) and type 7 stools fewer (0 versus 6, p = 0.03), while type 6 or 7 stools did not differ (19 versus 13); on 7 g only types 5 to 7 differed. A secondary analysis found no change in average pain, belching, bloating, gas or wellbeing scores in any arm.
Randomized, double-blind, placebo-controlled trial; 2-week corn starch run-in for all, then 30 g/day of MSPrebiotic® resistant potato starch (the maker's earlier potato starch, stated to be 70 percent resistant starch versus 60 percent for Solnul) or digestible corn starch (Amioca TF) for 12 weeks; registered NCT01977183; funded by the National Research Council of Canada and MSPrebiotics Inc., which supplied both products; glucose and LDL results appear in two companion papers, one written by a maker employee (Alfa et al. 2018, Clin Nutr)
84 adults who completed the study: 42 aged 70 or older (11 living in long-term care) and 42 aged 30 to 50, without diagnosed diabetes or prediabetes; about 21 per group.
Bifidobacterium rose more than on placebo in both age groups (p = 0.047 older, p = 0.006 mid-age), and stool butyrate rose slightly in older adults. In older adults, fasting glucose (p = 0.03), insulin (p = 0.009) and HOMA-IR (p = 0.009) changed more favorably than on placebo, with glucose about 7 percent lower; LP-IR did not differ, and no glucose or insulin measure changed in mid-age adults. Pain, bloating and flatulence scores stayed low and did not differ from placebo, bowel movement counts did not change, and LDL cholesterol did not change overall.