Energetic consequences of thermal and nonthermal food processing

Abstract

Processing food extensively by thermal and nonthermal techniques is a unique and universal human practice. Food processing increases palatability and edibility and has been argued to increase energy gain. Although energy gain is a well-known effect from cooking starch-rich foods, the idea that cooking meat increases energy gain has never been tested. Moreover, the relative energetic advantages of cooking and nonthermal processing have not been assessed, whether for meat or starch-rich foods. Here, we describe a system for characterizing the energetic effects of cooking and nonthermal food processing. Using mice as a model, we show that cooking substantially increases the energy gained from meat, leading to elevations in body mass that are not attributable to differences in food intake or activity levels. The positive energetic effects of cooking were found to be superior to the effects of pounding in both meat and starch-rich tubers, a conclusion further supported by food preferences in fasted animals. Our results indicate significant contributions from cooking to both modern and ancestral human energy budgets. They also illuminate a weakness in current food labeling practices, which systematically overestimate the caloric potential of poorly processed foods.

Fig. 1.

Changes in body mass on tuber diets. Mean cumulative change in body mass [±95% confidence interval (CI)] over 4 d in mice (n = 17) fed standardized ad libitum diets of organic sweet potato (I. batatas) served raw and whole (RW), raw and pounded (RP), cooked and whole (CW), and cooked and pounded (CP). Diets were administered based on a counterbalanced within-subjects study design.

Fig. 2.

Food preferences on tuber diets. Relative preferences among mice (n = 17) in the naïve (before exposure to any tuber diet) and experienced (after exposure to all tuber diets) conditions for organic sweet potato (I. batatas) served raw and whole (RW), raw and pounded (RP), cooked and whole (CW), and cooked and pounded (CP). Values shown reflect composite data from the two metrics of preference used in this study: first bite (diet consumed first given concurrent presentation of all diets) and total intake (grams consumed in 3 h corrected for desiccation). The composite value for a given diet is calculated as the average of the percentage of first bites and the percentage of total intake attributable to that diet. Naïve mice strongly preferred pounded tuber treatments (composite value χ²; cooking: P = 0.489, pounding: P < 0.001), whereas experienced mice strongly preferred cooked tuber treatments (composite value χ²; cooking: P < 0.001, pounding: P = 0.519).

Fig. 3.

Changes in body mass on meat diets. Mean cumulative change in body mass (±95% CI) over 4 d in mice (n = 16) fed standardized ad libitum diets of organic beef (B. taurus) eye round served raw and whole (RW), raw and pounded (RP), cooked and whole (CW), and cooked and pounded (CP). Diets were administered based on a counterbalanced within-subjects study design.

Fig. 4.

Food preferences on meat diets. Relative preferences among mice (n = 16) in the naïve (before exposure to any meat diet) and experienced (after exposure to all meat diets) conditions for organic beef (B. taurus) eye round served raw and whole (RW), raw and pounded (RP), cooked and whole (CW), and cooked and pounded (CP). Values shown reflect composite data from the two metrics of preference used in this study: first bite (diet consumed first given concurrent presentation of all diets) and total intake (grams consumed in 3 h corrected for desiccation). The composite value for a given diet is calculated as the average of the percentage of first bites and the percentage of total intake attributable to that diet. Mice preferred cooked meat diets in both the naïve condition (composite value χ²; cooking: P < 0.001, pounding: P = 0.049) and experienced condition (composite value χ²; cooking: P < 0.001, pounding: P = 0.386).