Fat in pistachios may not be completely absorbed by the body, meaning that they could be lower in available calories, according to new research presented at the Experimental Biology conference in Washington, D.C.
The researchers, from the US Department of Agriculture’s Agricultural Research Service (ARS), claim that this is the first human feeding study to look at how much energy is absorbed from pistachios, although previous clinical trials have suggested that fat from nuts may be poorly absorbed, indicating that nuts’ calorie levels may be lower than generally accepted.
In this study, researchers monitored diet and energy excretion through urine and feces – and their results suggest that pistachios may contain 5.9 percent fewer calories than previously thought due to reduced fat availability.
“Existing scientific research indicates that fat from nuts is poorly absorbed through the gastrointestinal tract,” said lead ARS researcher David Baer, supervisory research physiologist with the agency’s Beltsville Human Nutrition Research Center. “This study confirms that the fat from pistachio nuts, specifically, is not completed digested or absorbed, resulting in a lower energy value.”
Energy value of foods is most often allocated by using the Atwater general factor system, in which the main food components – protein, fat, and carbohydrate – have a single energy factor, regardless of the food in which they are found. Carbohydrates and proteins are considered to contain four calories per gram, fat nine calories per gram, and the system also includes a value of seven calories per gram of alcohol.
However, the researchers claim that this system may not work for measuring how much energy people actually get from pistachios.
In a randomized controlled feeding study involving 16 healthy adults, ARS researchers examined energy excretion when participants ate a diet containing no pistachios for three weeks; then when they ate 1.5oz (42g) of pistachios a day for three weeks; and then when they ate 3oz (84g) a day for another three weeks.
Their results suggest that the actual energy content of pistachio nuts is about 5.41kcal per gram, as opposed to the current accepted level of 5.67kcal per gram. This indicates that a typical 30g serving of pistachios may contain 160 calories - a six percent reduction on the generally accepted energy level.
The researchers wrote: “Accurate information about ME [metabolizable energy] content of foods is important for reliable food labeling so consumers can make informed dietary choices.”