When identical twins differ: an analysis of intrapair differences in the spontaneous eating behavior and attitudes of free-living monozygotic twins

Heredity has been shown to have major influences on the body size and ingestive behaviors of humans. However, environment is also important as evidenced by the fact that even identical twins can differ in body size and nutrient intake. To investigate the relative influence of heredity and environment, differences between the body size and food intake of 110 identical adult twin pairs who were living independently were studied with a 7-day diet diary technique. Differences within twin pairs (intrapair differences) in diet density were related to differences in daily intakes, but not with body size differences. On the other hand, cognitive restraint and disinhibition were related to intrapair differences in body size, but not intake. The fact that there are important environmental and psychological factors that influence intake and body size, even in individuals who have identical genotypes, supports the recently proposed general model of intake regulation. (C) 2004 Elsevier Inc. All rights reserved.