Influences of fat, energy, and time of day on mood and performance.

Paired studies testing the effects of lower energy high-fat, low-CHO meals (3181 kJ, fat:CHO energy ratio 54:41) and higher energy low-fat, high-CHO meals (3599 kJ, fat:CHO energy ratio 7:88) were conducted in 18 healthy males. The meals were eaten at 1030 h by group A (nine subjects) and 1230 h by group B (nine subjects). Subjective lassitude increased following ingestion of all four meals, but there was little change in performance. In addition, group A, but not group B, felt significantly less vigorous, imaginative, and antagonistic, and significantly more dreamy, feeble, and fatigued after the lower energy high-fat, low-CHO meal than after the higher energy low-fat, high-CHO meal. These results suggest that in the morning, fat exerts a greater depression on alertness and mood than carbohydrate irrespective of a reduction in energy content, but this effect varies according to the time at which food is eaten, and is less evident at lunch time.