title: Adjusting for energy intake--what measure to use in nutritional epidemiological studies?
abstract: BACKGROUND
  The measurement of energy intake in epidemiological studies is difficult. However, it is important that energy intake is assessed if epidemiological analyses are to correspond to isocaloric experiments. The aim of this study was to compare self-reported energy intake, physical activity, and body weight with energy expenditure measured by 4 days of heart rate monitoring with individual calibration of the relationship between heart rate and oxygen consumption.
  
  
  METHODS
  Volunteer sub-study of 97 men and women (mean ages 54 and 51 years respectively) within the European Investigation into Cancer (EPIC) study in Norfolk (UK). Dietary assessment of energy intake and physical activity was by self-report and weight was measured using standard techniques. Energy expenditure was assessed objectively by recording heart rate for 4 days following a calibration of the relationship between heart rate and oxygen consumption.
  
  
  RESULTS
  Self-reported energy intake by 7-day diary (mean 8.5 MJ/day) and food frequency questionnaire (FFQ) (mean 8.8 MJ/day) were significantly lower than objectively measured total energy expenditure (mean 11.2 MJ/day). The deattenuated partial correlations between total energy expenditure were 0.33 (7-day diary), 0.34 (FFQ), 0.50 (physical activity), and 0.56 (weight). Weight accounted for 31% (deattenuated) of the sum of squares about the mean of true energy intake after adjusting for age and sex. With the addition of self-reported physical activity, the model was significantly improved (R2 = 0.57). Adding energy either assessed by the diary or FFQ did not improve the model.
  
  
  CONCLUSIONS
  The results presented here indicate that to adjust for energy intake, for the purpose of replicating an isocaloric experiment in an observational epidemiological study, one would do considerably better adjusting for weight and physical activity, than adjusting for energy intake estimated from an FFQ.
authors.affiliation: MRC Epidemiology Unit, Strangeways Research Laboratory, Cambridge, CB1 8RN, UK.
authors.forename: Rupert W
authors.initials: RW
authors.lastname: Jakes
authors.forename: Nicholas E
authors.initials: NE
authors.lastname: Day
authors.forename: Robert
authors.initials: R
authors.lastname: Luben
authors.forename: Ailsa
authors.initials: A
authors.lastname: Welch
authors.forename: Sheila
authors.initials: S
authors.lastname: Bingham
authors.forename: Jo
authors.initials: J
authors.lastname: Mitchell
authors.forename: Susie
authors.initials: S
authors.lastname: Hennings
authors.forename: Kirsten
authors.initials: K
authors.lastname: Rennie
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Wareham
mesh_terms: D001835:Body Weight; D015930:Diet Records; D002149:Energy Intake; D004734:Energy Metabolism; D004812:Epidemiologic Methods; D015444:Exercise; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D009749:Nutrition Surveys; D011795:Surveys and Questionnaires