This invention provides a method of improving mood and learning capacity in a mammal by giving the mammal a meal of low protein food, followed by a second meal of high glycemic index carbohydrate. A composition to be given to a mammal to improve mood and learning capacity and to reduce aggressive behavior contains at least one tyrosine uptake competitive amino acid in a ratio of 0.5% to 2% to protein. The tyrosine competitive amino acid preferred is leucine, isoleucine or valine.