Discrepancy between Atwater factor predicted and empirically measured energy value of almonds in human diets

Authors: Novotny, Janet; Gebauer, Sarah; Baer, David

Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2012
Publication Date: 7/3/2012
Citation: Novotny Dura, J., Gebauer, S.K., Baer, D.J. 2012. Discrepancy between Atwater factor predicted and empirically measured energy value of almonds in human diets. American Journal of Clinical Nutrition. 96:296-301.

Interpretive Summary: Calories in food are often calculated using factors developed in the late 1890s by W. O. Atwater. However, these factors have not been validated for most foods, especially while individual foods are fed as part of a mixed diet, and they may not be accurate for certain food groups. Nuts are a food group for which evidence suggests that the Atwater factors may be poorly predictive. In this study, we determined the energy value of almonds in the human diet and compared the measured energy value to the value calculated from the Atwater factors. Eighteen healthy adults consumed a controlled diet for 18 days. Volunteers received at least two of three doses of almonds: 0 servings/d, 1.5 (1.5 oz) servings/day or 3 (3 oz) servings/day. During the final 9 days of the treatment period, volunteers collected all urine and feces, and samples of diets, feces, and urine were analyzed for energy and nutrient composition. Based on the amount consumed and excreted, the metabolizable energy content of the almonds was calculated. The energy content of almonds in the human diet was found to be 129 kcal per 1 oz serving. This value is significantly less than the determined amount using the Atwater factors, which is an energy content of 168-170 kcal/serving. The Atwater factors, when applied to almonds, result in a 32% overestimation in their energy content. These results should be of interest to allied health professionals, consumers and regulators responsible for advising clients and consumers.

Technical Abstract: Energy content of foods is primarily determined by the Atwater factors, which may not be accurate for certain food groups. Nuts are a food group for which evidence suggests that the Atwater factors may be poorly predictive. The objective of this study was to determine the energy value of almonds in the human diet and to compare the measured energy value to the value calculated from the Atwater factors. Eighteen healthy adults consumed a controlled diet or an almond containing diet for 18 days. Three dietary treatments were administered to subjects in a crossover design, and diets contained one of three almond doses: 0 g/d, 42 g/d, or 84 g/d. During the final 9 days of the treatment period, volunteers collected all urine and feces, and samples of diets, feces, and urine were analyzed for fat, nitrogen, fiber, ash, and energy. Subsequently, the metabolizable energy content of the almonds was calculated. The energy content of almonds in the human diet was found to be 4.6+/-0.8 kcal/g, equivalent to 129 kcal per 28 g serving. This is significantly less than the energy density of 6.0-6.1 kcal/g as determined by the Atwater factors, equivalent to an energy content of 168-170 kcal/serving. The Atwater factors, when applied to almonds, result in a 32% overestimation in their measured energy content.