title: Walnuts Consumed by Healthy Adults Provide Less Available Energy than Predicted by the Atwater Factors.
abstract: BACKGROUND
  Previous studies have shown that the metabolizable energy (ME) content (energy available to the body) of certain nuts is less than predicted by the Atwater factors. However, very few nuts have been investigated to date, and no information is available regarding the ME of walnuts.
  
  
  OBJECTIVE
  A study was conducted to determine the ME of walnuts when consumed as part of a typical American diet.
  
  
  METHODS
  Healthy adults (n = 18; mean age = 53.1 y; body mass index = 28.8 kg/m(2)) participated in a randomized crossover study with 2 treatment periods (3 wk each). The study was a fully controlled dietary feeding intervention in which the same base diet was consumed during each treatment period; the base diet was unsupplemented during one feeding period and supplemented with 42 g walnuts/d during the other feeding period. Base diet foods were reduced in equal proportions during the walnut period to achieve isocaloric food intake during the 2 periods. After a 9 d diet acclimation period, subjects collected all urine and feces for ∼1 wk (as marked by a Brilliant Blue fecal collection marker) for analysis of energy content. Administered diets, walnuts, and fecal and urine samples were subjected to bomb calorimetry, and the resulting data were used to calculate the ME of the walnuts.
  
  
  RESULTS
  One 28-g serving of walnuts contained 146 kcal (5.22 kcal/g), 39 kcal/serving less than the calculated value of 185 kcal/serving (6.61 kcal/g). The ME of the walnuts was 21% less than that predicted by the Atwater factors (P < 0.0001).
  
  
  CONCLUSIONS
  Consistent with other tree nuts, Atwater factors overestimate the metabolizable energy value of walnuts. These results could help explain the observations that consumers of nuts do not gain excessive weight and could improve the accuracy of food labeling. This trial was registered at clinicaltrials.gov as NCT01832909.
authors.affiliation: USDA, Agricultural Research Service, Beltsville Human Nutrition Research Center, Beltsville, MD David.Baer@ars.usda.gov.
authors.forename: David J
authors.identifier: http://orcid.org/0000-0003-3454-2097
authors.initials: DJ
authors.lastname: Baer
authors.affiliation: USDA, Agricultural Research Service, Beltsville Human Nutrition Research Center, Beltsville, MD.
authors.forename: Sarah K
authors.identifier: http://orcid.org/0000-0002-0823-7606
authors.initials: SK
authors.lastname: Gebauer
authors.affiliation: USDA, Agricultural Research Service, Beltsville Human Nutrition Research Center, Beltsville, MD.
authors.forename: Janet A
authors.initials: JA
authors.lastname: Novotny
mesh_terms: D001786:Blood Glucose / Q000378:metabolism; D001794:Blood Pressure; D015992:Body Mass Index; D008076:Cholesterol, HDL / Q000097:blood; D008078:Cholesterol, LDL / Q000097:blood; D018592:Cross-Over Studies; D066273:Diet, Western; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D004041:Dietary Fats / Q000008:administration & dosage; D004044:Dietary Proteins / Q000008:administration & dosage; D002149:Energy Intake; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D031324:Juglans; D008297:Male; D008875:Middle Aged; D009754:Nuts; D015430:Weight Gain
chemical_list: D001786:Blood Glucose; D008076:Cholesterol, HDL; D008078:Cholesterol, LDL; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D004044:Dietary Proteins
keywords: Atwater factors; calories; macronutrient digestibility; metabolizable energy; nuts; walnuts