Pediatric Highlight
International Journal of Obesity (2006) 30, 1501–1505. doi:10.1038/sj.ijo.0803333; published online 27 June 2006
Co-twin control designs for testing behavioral economic theories of child nutrition: methodological note
M S Faith1,2, E Rose3, P E Matz4, A Pietrobelli5 and L H Epstein6
- 1Weight and Eating Disorders Program, University of Pennsylvania, Philadelphia, PA, USA
- 2Children's Hospital of Philadelphia, Philadelphia, PA, USA
- 3Case Western Reserve University, Cleveland, USA
- 4New York, NY, USA
- 5Pediatric Unit, University of Verona, Verona, Italy
- 6Department of Pediatrics, University of Buffalo School of Medicine and Biomedical Sciences, Buffalo, USA
Correspondence: Dr MS Faith, Weight and Eating Disorders Program, University of Pennsylvania School of Medicine, 3535 Market Street, 3rd Floor, Philadelphia, PA 19104, USA. E-mail: mfaith@mail.med.upenn.edu
Received 7 January 2005; Revised 25 May 2005; Accepted 6 June 2005; Published online 27 June 2006.
Abstract
Objective:
To illustrate the use and potential efficiency of the co-twin control design for testing behavioral economic theories of child nutrition.
Design:
Co-twin control design, in which participating twins ate an ad libitum lunch on two laboratory visits. At visit 1, child food choices were not reinforced. On visit 2, twins were randomized to conditions such that one twin was reinforced for each fruit and vegetable serving consumed during lunch ('contingent') while his co-twin was reinforced irrespective of food intake ('non-contingent').
Subjects:
Six male twins, 5 years old, from three monozygotic twin pairs.
Measurements:
Ad libitum intake of total energy (kcals), fat (kcals), and fruits and vegetables (servings) from the protocol test meals on the two visits.
Results:
Compared to twins receiving non-contingent reinforcement, twins receiving contingent reinforcement increased fruit and vegetable intake by 2.0 servings, reduced fat intake 106.3 kcals, and reduced total energy intake by 112.7 kcals. The relative efficiency of the co-twin control design compared to a conventional between-groups design of unrelated children was most powerful for detecting 'substitution effects' (i.e., reduced total energy and fat intake) more so than for detecting increased fruit and vegetable intake.
Conclusion:
Genetically informative studies, including the co-twin control design, can provide conceptually elegant and efficient strategies for testing environmental theories of child nutrition and obesity.
Keywords:
behavioral economics, twins, child nutrition, behavior, food choice, childhood obesity
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