Evolutionary Perspectives on Obesity and Associated Metabolic Conditions, and a Test of the Ancestral Diet Hypothesis

Obesity, type 2 diabetes and other associated metabolic diseases have become blatant epidemic diseases over the last few decades. All of these diseases have a negative impact on human well-being and function at all stages of the life-cycle. Does evolutionary theory provide any utility towards understanding these conditions? Could these dysfunctional conditions be studied as any other functional traits—like the beaks of Darwin’s finches? How has evolutionary theory been invoked to explain the etiology and prevalence of these diseases? Could one use an evolutionary framework to organize the various evolutionary hypothesis of obesity and associated metabolic conditions? These are some of the questions this dissertation has attempted to answer. This dissertation provides a framework to study any trait from an evolutionary perspective; whether biological or cultural. This framework is then utilized to organize existing evolutionary hypotheses of obesity. Many of these invoke natural selection, some invoke constraints-based processes, some highlight the importance of developmental and maternal environment and one of the hypothesis points towards the importance of genetic drift. Majority of the hypotheses see obesity as a consequence of an evolutionary mismatch between humans and the drastically novel environment they inhabit in comparison to their ancestors. Five of these hypotheses were reviewed to unravel how they explain the mechanism, development, function, and phylogeny of obesity—thrifty genotype, thrifty phenotype, protein leverage, microbiome and the Ancestral diet hypothesis. Ancestral diet hypothesis, a hypothesis of dietary mismatch, is identified as a well-rounded hypothesis. This hypothesis argues the human dietary needs were shaped during the origin and evolution of Homo genus. This dietary environment changed rapidly with the onset of agriculture and industrial revolution which introduced novel foods in the human diet (grains, dairy and refined products) and is hypothesized to be the root cause of obesity and associated metabolic conditions. Results of a test of the Ancestral diet hypothesis in the form a dietary trial is provided where it is shown that dietary carbohydrates and their sources—grains, sugar and vegetables—are major predictors of changes in health-related anthropometric markers