Inulin-type fructans are fermented by gut bacteria to yield SCFA, including butyrate which is trophic for colonocytes and induces glutathione S-transferases (GST) that detoxify carcinogens. Since little is known on similar effects by complex fermentation samples, we studied related products in non-transformed human colonocytes. Inulin enriched with oligofructose (1 : 1, Synergy1) was fermented with human gut flora. SCFA were quantified and a SCFA mixture was prepared accordingly. Colonocytes were incubated (4–12 h) with the Synergy1 fermentation supernatant (SFS), faeces control, a mixture of the three major SCFA (each 0–15 %, v/v) or butyrate (0–50 mm). Metabolic activity was determined to assess trophic effects and cytotoxicity. Expression of ninety-six genes related to biotransformation was studied using cDNA macroarrays. Results on modulated GST were reassessed with real-time PCR and GST activity was measured. Fermentation of inulin resulted in 2–3-fold increases of SCFA. The samples were non-cytotoxic. SFS increased metabolic activity, pointing to trophic effects. The samples modulated gene expression with different response patterns. Key results were that GSTM2 (2·0-fold) and GSTM5 (2·2-fold) were enhanced by SFS, whereas the SCFA mixture reduced expression. The faeces control enhanced GSTA4 (2·0-fold), but reduced GSTM2 (0·2-fold) and GSTM5 (0·2-fold). Real-time qPCR confirmed the induction of GSTM2 and GSTM5 by SFS and of GSTA4 and GSTT2 by butyrate. Activity of GST was not modulated. High concentrations of fermentation products were well tolerated by primary colonocytes, pointing to trophic effects. The induction of GST by the SFS may protect the cells from carcinogenic compounds.