Deposition of excess dietary energy occurs if energy intake exceeds ex
penditure. Anthropometric differences between breast-fed and formula-f
ed infants due to differences in energy deposition are frequently repo
rted. It has been suggested that infant obesity may result from decrea
sed levels of energy expenditure on physical activity. Infant diet may
therefore influence energy balance by affecting behaviour and hence e
nergy expenditure. Behavioural and motor activity of 25 formula-fed an
d 25 breast-fed infants were compared using activity diaries, temperam
ent questionnaires and actometers. There were no anthropometric differ
ences between the two groups. The breast-fed infants fed significantly
more slowly than the formula-fed infants despite taking in similar mi
lk volumes, and also fed significantly more frequently. Otherwise ther
e were no significant differences between the two groups with respect
to the daily time spent awake and content, asleep, fussy, or crying, n
or with respect to gross motor activity and temperament. It is unlikel
y that energy balance of the two groups differed significantly on acco
unt of behavioural activity.