Previous studies have suggested that lipid from nuts is more poorly absorbed than that from other food sources. If lipid from nuts is poorly absorbed, then the metabolisable energy contained in the nuts is less than that predicted by the Atwater general factors. A crossover feeding study was conducted in which sixteen volunteers consumed pistachios for 3 weeks as part of a controlled diet. Pistachio doses were 0, 42 and 84 g/d. Urine and faecal samples were collected, and urine, faeces and diet were analysed for N, fat, total dietary fibre, ash and combustible energy. Blood was also collected after each treatment period and analysed for plasma lipids. Energy value of pistachio nuts was calculated from differences in energy excretion during the different dietary treatments. The measured energy density of pistachios was found to be 22·6 kJ/g, which is 5 % less than the currently accepted energy value of 23·7 kJ/g, as calculated using the Atwater general factors. The pistachio nut intervention lowered LDL-cholesterol by 6 %, but did not significantly change plasma total cholesterol, HDL-cholesterol or TAG. In conclusion, pistachio nuts contain less metabolisable energy than that calculated from the Atwater general factors. Accurate information about metabolisable energy content of foods is important for reliable food labelling.