title: Validation of an inexpensive and accurate mathematical method to measure long-term changes in free-living energy intake.
abstract: BACKGROUND
  Accurate measurement of free-living energy intake (EI) over long periods is imperative for understanding obesity and its treatment. Unfortunately, traditional methods rely on self-report and are notoriously inaccurate. Although EI can be indirectly estimated by the intake-balance method, this technique is prohibitively labor-intensive and expensive, requiring repeated measures of energy expenditure via doubly labeled water (DLW) along with multiple dual-energy X-ray absorptiometry (DXA) scans to measure changes in body energy stores.
  
  
  OBJECTIVE
  Our objective was to validate a mathematical method to measure long-term changes in free-living energy intake.
  
  
  METHODS
  We measured body weight and EI changes (ΔEI) over 4 time intervals by using the intake-balance method in 140 individuals who underwent 2 y of caloric restriction as part of the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy study. We compared the ΔEI values calculated by using DLW/DXA with those obtained by using a mathematical model of human metabolism whose only inputs were the initial demographic information and repeated body weight data.
  
  
  RESULTS
  The mean ΔEI values calculated by the model were within 40 kcal/d of the DLW/DXA method throughout the 2-y study. For individual subjects, the overall root mean square deviation between the model and DLW/DXA method was 215 kcal/d, and most of the model-calculated ΔEI values were within 132 kcal/d of the DLW/DXA method.
  
  
  CONCLUSIONS
  Accurate and inexpensive estimates of ΔEI that are comparable to the DLW/DXA method can be obtained by using a mathematical model and repeated body weight measurements.
authors.affiliation: National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD; and.
authors.forename: Arjun
authors.initials: A
authors.lastname: Sanghvi
authors.affiliation: Pennington Biomedical Research Center, Baton Rouge, LA.
authors.forename: Leanne M
authors.initials: LM
authors.lastname: Redman
authors.affiliation: Pennington Biomedical Research Center, Baton Rouge, LA.
authors.forename: Corby K
authors.initials: CK
authors.lastname: Martin
authors.affiliation: Pennington Biomedical Research Center, Baton Rouge, LA.
authors.forename: Eric
authors.initials: E
authors.lastname: Ravussin
authors.affiliation: National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD; and kevinh@niddk.nih.gov.
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Hall
mesh_terms: D000328:Adult; D000465:Algorithms; D015992:Body Mass Index; D001835:Body Weight; D031204:Caloric Restriction; D004038:Diet, Reducing; D002149:Energy Intake; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D054586:National Institute of Diabetes and Digestive and Kidney Diseases (U.S.); D015596:Nutrition Assessment; D050177:Overweight / Q000178:diet therapy* / Q000378:metabolism; D015203:Reproducibility of Results; D014481:United States; D015431:Weight Loss; D055815:Young Adult
keywords: caloric restriction; dietary assessment; energy balance; energy intake; mathematical modeling; weight loss