Smith, T. J., Lieberman, H. R., Karl, J. P., McGraw, S., Pikosky, M. A., Glickman, E. L., Grediagin, A., & Young, A. J. (2006). A high protein diet exacerbates the adverse effects of an energy deficit on mood state. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 1538.

This investigation compared the effects of eucaloric diets containing high versus moderate protein content on mood state in volunteers experiencing an exercise-induced energy deficit. Male volunteers N = 12) were subjected to a 1000 kcal/d exercise-induced energy deficit for seven days (D5-11) following four baseline days (BL) of strictly controlled energy balance. Five Ss received a moderate protein diet (MP) containing (0.9 g/kgBW), and seven Ss received a high protein diet (1.8 g/kgBW). Carbohydrate intake was equivalent in both groups while fat was adjusted for protein intake in the high protein group to achieve similar total energy intakes for both groups. Energy expenditure was assessed daily. Mood state was assessed by the Profile of Mood States Questionnaire (POMS).

Energy deficit and weight loss were equivalent between groups. Both groups showed a linear increase in fatigue and depression. In addition, the high protein group demonstrated a decline in vigor, an increase in anger, and an increase in total mood disturbance over time.

Implication. A decrease in vigor and increases in anger and total mood disturbance, suggest that increased dietary protein content negatively impacts mood state during an exercise-induced energy deficit. Whether the adverse effects are due to an increase in protein, decrease in dietary fat, or a combination, was not determined.

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