Energetic Consequences of Thermal and Non-Thermal Food Processing
All human societies process their food extensively by thermal and non-thermal means. This feature distinguishes us from other species, and may even be compulsory given that humans are biologically committed to an energy-rich diet that is easy to chew and digest. Yet the energetic consequences of food processing remain largely unknown. This dissertation tests the fundamental hypothesis that thermal and non-thermal processing lead to biologically relevant increases in energy gain from protein-rich meat and starch-rich tubers, two major caloric resources for modern and ancestral humans that present divergent structural and macronutrient profiles. The energetic consequences of food processing are evaluated using three indices of energy gain, each of which account for costs not currently captured by conventional biochemical assessments of dietary energy value. Chapter 2 investigates the effects of cooking and pounding on net energy gain as indexed by changes in body mass, controlling for differences in food intake and activity level. Chapter 3 examines the effect of cooking and pounding on diet-induced thermogenesis, the metabolic cost of food digestion. Chapter 4 considers the effort required to engage in food processing, arguing that the advantageous ratio of benefit to cost has likely had important effects on human life history. By each of these definitions of energy gain, food processing is shown to have substantial energetic significance. Overall, energetic gains due to thermal processing exceeded those of non-thermal processing, consistent with recent proposals that the adoption of cooking had a particularly important influence on human biology. Gains due to food processing were observed in both meat and tuber substrates, supporting a transformative role for habitual food processing in the evolution and maintenance of the human energy budget.