Doctoral Dissertation Improvement: Impacts of Food Processing on Diet-Induced Thermogenesis

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All human societies regularly process their foods by thermal and non-thermal means. This feature distinguishes humans from other species, and may even be compulsory from an energetic perspective, given that we possess relatively small molars and gastrointestinal tracts that commit us to an easily digestible diet. Yet the energetic significance of food processing and its evolutionary implications have barely been considered. This study tests the hypothesis that thermal and non-thermal processing lower the metabolic cost of food digestion, known as diet-induced thermogenesis (DIT). Effects will be evaluated for tubers and meat, foods widely exploited by humans and believed to have been critical resources for ancestral hominins. In theory, processing of these foods should result in a loss of structural integrity that lowers DIT due to reduced chewing and gastric effort, as well as increased access by digestive acids and enzymes. Since heat should weaken food structural integrity to a greater extent by gelatinizing starch and collagen, it is further predicted that the effects of thermal processing will exceed those of non-thermal processing. To evaluate these predictions, energy expenditure data are collected via respirometry from subjects before and after standardized meals served raw and whole, raw and pounded, roasted and whole, or roasted and pounded, based on a counterbalanced within-subjects design. Rats will be used as model organisms in the interests of low cost and high control, but a subset of trials will be replicated using human subjects to validate the animal model. This study will quantify the impacts of thermal and non-thermal processing on DIT, an important factor in energy balance. Results will improve our understanding of the energetic returns of food processing and inform models of hominin transitions toward higher dietary quality. Low DIT has been implicated as a factor in the development of obesity. By determining the effects of food processing on DIT, this research contributes basic data that could help consumers influence the partitioning of meal energy to metabolism versus body stores. Results will thus be communicated broadly to peer-reviewed journals and conferences in anthropology and nutrition, as well as public forums. This doctoral dissertation research project will also contribute to the professional development of a female graduate student.