CMAJ • January 3, 2006; 174 (1). doi:10.1503/cmaj.050649.
© 2006 CMA Media Inc. or its licensors
All editorial matter in CMAJ represents the opinions of the authors and not necessarily those of the Canadian Medical Association.
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Why don't pigs get diabetes? Explanations for variations in diabetes susceptibility in human populations living in a diabetogenic environment

Hertzel C. Gerstein * and Laura Waltman{dagger}

*Division of Endocrinology and Metabolism, Population Health Research Institute, McMaster University, Hamilton Health Sciences, Hamilton, Ont.; {dagger}Department of Nutritional Science, University of Toronto, St. Michael's Hospital, Toronto, Ont.



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  		Fig. 1: Model showing estimated effect of reproductive fitness on the prevalence of diabetes. In this model, if people with type 2 diabetes have a reproductive success rate that is 10% lower than that among people without diabetes (represented by dotted line), it will take 12–25 generations for the prevalence of diabetes to fall from 30%–40% (currently seen in Aboriginal populations) to 5%–10% (currently seen in populations of European descent).

 


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  		Fig. 2: Prevalence of diabetes in populations according to their ability to adapt genetically to the environment. When the environment becomes diabetogenic (i.e., promotes inactivity and increased food consumption), the number of people who are not metabolically adapted (naive) to the new environment increases; diabetes and its antecedents will develop more frequently and earlier in these people than in their peers, and their reproductive success will be reduced. Natural selection will favour the remaining individuals, and after 12–25 generations, the normal distribution of the population's ability to cope metabolically with the environment will shift to the right, and the prevalence of diabetes will fall. A further change in the environment, or the introduction of a naive population to the existing environment, starts the process over.