A 2025 clinical trial compared inulin glycemic effects with FOS effects. I won’t curate its gut microbiota results as these have unresolved measurement problems:

“In this study, we conducted a randomized, double-blind investigation to examine the impact of inulin and fructooligosaccharides (FOS) on glycemic metabolism in overweight/obese and healthy adults.

Inulin and FOS are both fructans composed of fructose units, but they differ in their degree of polymerization (DP) and chain length, which lead to differences in their physicochemical properties and physiological effects. Inulin typically has a longer chain length, with a DP ≥ 10, resulting in lower solubility and slower fermentation in the distal colon. FOS consists of shorter chains, with a DP 2 to 9, presenting higher solubility and undergoing rapid fermentation in the proximal colon. These differences affect their impact on short-chain fatty acid (SCFA) production, gut microbiota modulation, and subsequently results in different effects on host metabolism.

131 participants were recruited and randomized into three groups: inulin (N = 44), FOS (N = 43), and control (N = 44). Each group was conducted with a daily supplement of 15 g FOS, inulin, and maltodextrin as placebo and lasted for 4 weeks. Dosage was determined based on our previous clinical trials in the healthy young population, which reported using 16 g/day has no risk of adverse effects. Subjects were still recommended to take a half dose in the first 2 days to promote adaptation to the prebiotics and minimize gastrointestinal symptoms. Products were suggested to add to drinks such as coffee, tea, or milk.

Inulin significantly reduced glucose levels at 1 h and 2 h during oral glucose tolerance test (OGTT), increased fasting insulin, and lowered homocysteine (HCY) levels in overweight/obese individuals. These effects were not observed in healthy individuals.

In contrast, although FOS significantly decreased HCY, it did not improve glycemic metrics in either group.”

https://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-025-04189-6 “Differential effects of inulin and fructooligosaccharides on gut microbiota composition and glycemic metabolism in overweight/obese and healthy individuals: a randomized, double-blind clinical trial”

---

Prior research found:

“A 2010 gastrointestinal tolerance of chicory inulin products study indicated that 10 g/day of native inulin were well-tolerated in healthy, young adults. Over this dose would induce mild gastrointestinal symptoms.”

So a lead-in half-dose probably wouldn’t be needed for people to start a 10 gram inulin dose.