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Photo: Pistachios. Link to photo information
ARS scientists have shown that some tree nuts such as pistachios actually have fewer calories than previously thought by improving the method used for estimating calories. Click the image for more information about it.

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ARS Scientists Develop Improved Method to Estimate Calories

By Rosalie Marion Bliss
September 16, 2013

U.S. Department of Agriculture (USDA) scientists have improved the method for estimating calories in tree nuts, showing that there are fewer calories in pistachios and almonds than previously thought. The modified method should also work well for other foods, according to the scientists with the Agricultural Research Service (ARS), USDA's chief intramural scientific research agency.

Chewing begins the digestive process of liberating nutrients from food. This process is necessary before nutrients are considered "bioaccessible." In theory, the fat within some hard foods is not completely absorbed because it's difficult to digest the food's cell walls, which contain the fat.

Physiologists David Baer and Janet Novotny at the ARS Beltsville Human Nutrition Research Center in Beltsville, Md., fed 16 healthy adults pistachios at three different levels: none, 1.5 ounces per day, and three ounces per day, along with a background, or "base," nut-free diet. The volunteers ate each pistachio level for 18 days. Researchers collected and analyzed urine and stool samples from all feeding periods. This analysis consisted of measuring calories in the foods that were fed to volunteers (energy in) and measuring the same foods' excreted remains (energy out).

Novotny, who is also a mathematician, wrote a series of algebraic equations that were used to evaluate data gathered from the biological samples. This analysis enabled the team to measure the calories specifically supplied by the target food—the pistachios—even though the nuts were consumed along with the base diet.

The study suggests that the caloric value of pistachios has likely been overestimated by about 5 percent, because the fat from the nuts wasn't completely absorbed by the intestinal tract. The study, published in the British Journal of Nutrition in 2011, was supported by USDA and Paramount Farms, Inc. in Los Angeles, Calif.

Read more about the researchers' similar human clinical trial, in which they used the modified method to compute the number of calories in almonds, in the September 2013 issue of Agricultural Research magazine.