title: Personal and social norms for food portion sizes in lean and obese adults.
abstract: BACKGROUND
  Portion size is an important component of dietary advice for weight control, but little is known about what portion sizes people consider 'normal'. This study determined the effect of body mass index (BMI), gender, dietary restraint and liking of the food on personal and social portion size norms for a range of foods and the degree of certainty over the norms.
  
  
  METHODS
  Thirty lean (BMI 20-25 kg m(-)(2)) and 30 obese (BMI 30-35 kg m(-)(2)) men and women (aged 18-60 years) viewed 17 different portion sizes of 12 foods on a computer screen on two occasions a week apart. Participants responded 'more' or 'less' to each photograph reflecting personal portion size preference or perceived portion sizes of others. Personal and social norms for portion sizes of each food were determined using the method of constant stimuli giving a sigmoidal curve of the probability of answering 'less' over a range of portion sizes. The slope of the sigmoid at the norm gave a measure of certainty about the norm. Regression models were used to examine the effect of BMI, gender, dietary restraint and liking of the food on personal norms, social norms, the relationship between norms, and the slopes.
  
  
  RESULTS
  Personal norms were significantly larger in the obese (P=0.026), men (P<0.001), those with lower dietary restraint (P<0.001), and those with higher liking for the food (P<0.001). Social norms were larger for women (P=0.012). The slopes at the norms were 30% shallower in the obese and in men (P<0.001).
  
  
  CONCLUSIONS
  Larger personal norms for portion size among the obese, men, those with lower dietary restraint and those with higher liking for a food imply greater consumption, which may undermine weight control. Shallower slopes for norms in the obese and in men may imply less clearly defined habitual portion sizes.
authors: Medical Research Council Human Nutrition Research, Elsie Widdowson Laboratory, Cambridge, UK.
authors: H B
authors: HB
authors: Lewis
authors: Behaviour and Health Research Unit, University of Cambridge, Cambridge, UK.
authors: S E
authors: SE
authors: Forwood
authors: Medical Research Council Human Nutrition Research, Elsie Widdowson Laboratory, Cambridge, UK.
authors: A L
authors: AL
authors: Ahern
authors: School of Psychology, University of Birmingham, Birmingham, UK.
authors: K
authors: K
authors: Verlaers
authors: Psychological Sciences, University of Liverpool, Liverpool, UK.
authors: E
authors: E
authors: Robinson
authors: School of Psychology, University of Birmingham, Birmingham, UK.
authors: S
authors: S
authors: Higgs
authors: Medical Research Council Human Nutrition Research, Elsie Widdowson Laboratory, Cambridge, UK.
authors: S A
authors: SA
authors: Jebb
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D015992:Body Mass Index; D003463:Cues; D004034:Diet Surveys; D002149:Energy Intake; D005260:Female; D005518:Food Preferences; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000523:psychology*; D064787:Portion Size / Q000523:psychology* / Q000706:statistics & numerical data; D066262:Social Norms; D013851:Thinness / Q000523:psychology*; D006113:United Kingdom