Contributions of Food Processing to Dietary Energy Harvest

The caloric consequences of a highly processed diet have remained unclear, in part because few studies have evaluated energy gains associated with a processed diet independently of other lifestyle factors, and in part because the metabolizable energy values reported widely in the scientific literature and on nutrition labels suggest that food processing has little caloric effect. However recent controlled experiments in our lab employing animal models show that processing by thermal and/or non-thermal means contributes importantly to energy harvest from plant and animal foods. For instance, controlling for food intake and activity, omnivorous adult mice exhibited increased body mass outcomes when eating cooked and/or pounded sweet potatoes or cooked beef versus when eating these foods in unprocessed form. Related experiments revealed these incremental net energy gains to be attributable to higher rates of nutrient assimilation in the small intestine as well as reduced diet-induced thermogenesis, the metabolic cost of digestion. These aspects of digestion are not represented in the Atwater factors typically used in the determination of metabolizable energy value. Thus researchers who report Atwater-based energy values as well as consumers who utilize nutrition labels to manage their caloric intake will necessarily underestimate the energetic gains associated with a processed diet. Given the long human history of food processing and its universal practice among modern populations, future work to improve our understanding of the energetic consequences of a processed diet promises fundamental insights into human biology, the energetic gains that fueled our evolution and the resulting commitments to an energy-rich diet that now sometimes threaten us.