Benefits
Stool frequency and stool output
In 7 older men, 10 g/day for 30 days doubled defecation frequency and raised wet stool output 70% against a prior low-fiber period, and in 13 older adults wet fecal mass rose 24% over a placebo period. Neither study was randomized and enemas were allowed. In an unpublished 4-week randomized placebo-controlled trial in healthy adults, 36 or 54 g/day did not change bowel movements.
Gut bacteria counts across human studies
In a study of 13 older adults without randomization, 10 g/day raised fecal bifidobacteria and lactobacilli over a placebo period. In a randomized placebo-controlled screening in healthy adults, 10 g/day for 7 days did not raise bifidobacteria, and 15 g/day of an IMO product for 1 week left microbiota diversity unchanged in healthy women. Bacteria counts are markers, not health outcomes.
Blood glucose and insulin rise about as much as after dextrose
In two randomized crossover tests in healthy adults, IMO syrups matched to 50 g of carbohydrate raised blood glucose and insulin by amounts that did not differ significantly from dextrose, even for a syrup with under 10% simple sugars. A tracer study also found glucose and insulin rose within 30 minutes. People counting carbohydrates should count IMO.
Slower stomach emptying than maltodextrin in a yogurt meal
In a randomized crossover trial in 20 adults, a yogurt carrying 26 g of IMO emptied from the stomach moderately but significantly more slowly than one with rapidly digested maltodextrin, consistent with IMO being digested slowly along the small intestine. About half of participants responded, and appetite ratings did not differ.
Blood cholesterol in small studies
In 13 older adults, total and LDL cholesterol were lower during 10 g/day IMO than during a placebo period, without randomization. In 20 hemodialysis patients, 30 g/day was reported to lower total cholesterol and triglycerides, but the FDA found LDL cholesterol did not differ from controls and judged the evidence inconsistent, noting no effect in a trial in healthy adults.
Digestive tolerance at large single servings
A single serving of IMO syrup giving 50 g of carbohydrate caused no more gastrointestinal symptoms or breath hydrogen than dextrose in 26 healthy adults. In a 1-week crossover, bloating or gas was reported by 25% of women on 15 g/day of an IMO product against 48% on inulin. An EU safety review accepted tolerability at up to 120 g/day.
Mechanism of action
Digested by small intestinal enzymes
The sucrase-isomaltase enzyme on the lining of the small intestine can split alpha-1,6 bonds. In lab tests, recombinant human sucrase-isomaltase broke IMOs down fully to glucose, only more slowly than linear malto-oligosaccharides, and breath hydrogen after IMO was a small fraction of that after FOS, showing little reached the colon.
A smaller fraction fermented in the colon
A tracer study estimated that part of IMO is digested and the rest fermented by gut bacteria, giving an energy value of about 75% of maltose. In studies of older adults, fecal acetate and propionate rose during IMO intake, a sign that some IMO reached colonic bacteria.
Slow digestion and the ileal brake
Because IMO is digested slowly, some of it can reach the lower small intestine, which is thought to trigger the ileal brake, a feedback signal that slows stomach emptying. A crossover trial found modestly slower stomach emptying after IMO, without a change in appetite ratings.
Why lab fiber tests can overstate IMO fiber
Standard fiber assays use a fungal enzyme that barely cuts alpha-1,6 bonds, so IMO can test as fiber in the lab even though human intestinal enzymes digest it. An industry survey of commercial IMO ingredients reported that likely glycemic impact may not match fiber claims on labels.
Clinical trials
Two randomized, double-blind crossover studies; single doses of IMO syrup matched to 50 g of carbohydrate against 50 g of dextrose; study 1 measured glucose, insulin and breath hydrogen over 4 to 24 hours, study 2 measured glucose over 2 hours. Written by employees of Ingredion, which made the syrups. (Gourineni et al. 2018, Nutrients)
Healthy adults: 26 in study 1 and 10 in study 2.
Glucose and insulin responses to IMO did not differ significantly from dextrose over 4 hours; glucose area was about 15% lower (p = 0.058), and lower only from 2 to 4 hours (p = 0.008). Breath hydrogen and symptom scores matched dextrose. In study 2, neither IMO syrup, including one with under 10% simple sugars, differed from dextrose (p = 0.662). The authors concluded IMO is digestible.
Comparison study; 10 g and then 20 g of each oligosaccharide at 1-week intervals, with breath hydrogen measured for 7 hours. Funded by Siebold University of Nagasaki. (Oku et al. 2003, Eur J Clin Nutr)
Healthy young adults in Japan (9 men and 29 women took part).
After 10 g, breath hydrogen area was 9768 ppm with FOS, 3662 ppm with galactosyl-sucrose and 831 ppm with IMO. The authors concluded IMO was readily hydrolyzed by small intestinal enzymes, so little reached the colon for fermentation.
Before-and-after study without randomization or blinding; 30-day low-fiber control period, then 30 days of 10 g/day IMO active components. (Chen et al. 2001, J Am Coll Nutr)
7 older men with constipation in Taiwan.
During the IMO period, defecation frequency doubled, wet stool output rose 70% and dry stool weight 55%, mostly from bacterial mass, and fecal acetate and propionate rose. Enemas were allowed during the study, and the FDA later found the independent effect of IMO could not be evaluated.
Diet-controlled study in the same people without randomization: 4-week placebo period, two 4-week periods of 10 g/day IMO, then 4 weeks off IMO. (Yen et al. 2011, Nutrition)
13 constipated older adults (mean age 82.5) in Taiwan.
Fecal bifidobacteria, lactobacilli and bacteroides rose and clostridia fell; wet fecal mass rose 24% and spontaneous defecation rose in the second IMO period only. Total and LDL cholesterol were lower than in the placebo or post period. Effects faded after IMO stopped. Enemas were allowed, and the FDA called the cholesterol results inconsistent across comparisons.
Double-blind, randomized, placebo-controlled parallel-group screening phase; 10 g/day of each carbohydrate or placebo for 7 days, 8 people per group. (Bouhnik et al. 2004, Am J Clin Nutr)
Healthy volunteers in France.
IMO did not raise fecal bifidobacteria, nor did lactulose or long-chain inulin, while short-chain FOS, soybean oligosaccharides, galacto-oligosaccharides and resistant starch did. IMO was not taken into the dose-response phase.
Crossover study without a placebo; 15 g/day of Vitafiber IMO, inulin or a fiber blend for 1 week each, with 2-week washouts. Funded by Australian public research grants. (Tan et al. 2023, Gut Microbes)
Healthy women aged 30 to 65 (34 enrolled, 28 completed).
Vitafiber did not change gut microbiota diversity or any bacterial phylum, and post-Vitafiber samples could not be told apart from baseline; the authors wrote it had the least effect of the three on microbiota, short-chain fatty acids and immune phenotypes. Bloating or gas was reported by 25% on Vitafiber and 48% on inulin.
Five-arm randomized, double-blind crossover trial; yogurts with 26 g of IMO, raw corn starch, sucromalt, an IMO and sucromalt mix, or maltodextrin; outcomes over 4 hours. Several authors employed by General Mills; registered retrospectively as NCT03630445. (Chegeni et al. 2022, Eur J Nutr)
20 adults (9 women, 11 men).
Gastric half-emptying time was moderately but significantly longer with IMO and with raw corn starch than with maltodextrin, with about half of participants responding. Appetite ratings did not differ. The trial treated IMO as a slowly digestible carbohydrate.