In animals, colonic infusion of SCFA does not affect glucagon-like peptide-1 (GLP-1) release whereas intravenous infusion does and SCFA may directly stimulate peptide YY (PYY) release. It is unknown whether SCFA and their route of administration affect human blood concentrations of GLP-1 and PYY. Our aim was to conduct a pilot study to determine the effects of intravenous and rectal acetate on blood concentrations of GLP-1, PYY, ghrelin, adiponectin and TNF-α in hyperinsulinaemic human subjects. Six hyperinsulinaemic female subjects were given 20 mmol sodium acetate intravenously, 60 mmol acetate rectally, or normal saline rectally or intravenously on four separate occasions in randomised order, with blood samples collected at 0, 10, 15, 30, 45 and 60 min. Change in plasma PYY was significantly higher after acetate and rectal infusions (9·69 and 13·78 pg/ml) compared with saline and intravenous (0·60 and − 3·1 pg/ml; P < 0·01), respectively. Change in plasma GLP-1 was increased by rectal and acetate infusions (0·25 and 0·23 mmol/l) v. intravenous and saline ( − 0·26 and − 0·19 mmol/l; P < 0·01). Acetate decreased TNF-α v. saline ( − 0·8 and 0·15 pg/ml; P < 0·05). Rectal infusions increased TNF-α and ghrelin (0·2 and 98·27 pg/ml) v. intravenous ( − 0·9 and − 40 pg/ml; P < 0·01). There was no effect of treatment on plasma adiponectin. These preliminary results suggest that acetate raises plasma PYY and GLP-1, and suppresses TNF-α. Also, distending the rectum increases PYY, GLP-1, TNF-α and ghrelin in hyperinsulinaemic females. Increasing colonic fermentation products, particularly acetate, could yield a new mechanism for modifying weight gain.