Growth tables used to chart a baby's development may be inaccurate, on-going research suggests.
By Ania Lichtarowicz
BBC World Service health reporter
The World Health Organization study found they may over-estimate how quickly babies should put on weight.
This may have caused unnecessary concern about for breastfed babies, who gain weight more slowly.
The research was dicussed at a meeting organised by the London School of Hygiene and Tropical Medicine and the International Obesity Task Force.
The child development growth charts in widspread use are largely based on studies of formula fed children from more than 20 years ago.
Formula fed babies tend to put weight on faster than their breastfed counterparts.
So, although it is widely accepted that breast milk provides babies with the best possible combination of nutrients, the charts appeared to suggest that many breastfed children were failing to thrive - even after just two or three months.
The latest WHO study, of 8,440 children from six countries, found that target weights for two and three-year-olds were 15% to 20% too high.
And the charts suggest healthy one-year-old weighs between 22.5lb (10.2kg) and 28.5lb (12.93kg), when in fact the true healthy weight is 21lb (9.53kg) to 26lb (11.79kg), they say.
The researchers say the current overfeeding of babies could explain in part why this generation of adults is the fattest ever.
The WHO will release new growth charts based on breast-fed babies at the end of the year.
Researcher Dr Mecedes de Onis said: "The new standards provide a much better description of the physiological growth and they establish that breast fed infants are the biological norm.
"Paediatricians will be able to congratulate parents on having exclusively breast fed their infants instead of spending time as they do now in trying to reassure them that the apparent growth faltering of the baby is not a reason for concern and is due to the imperfections of the growth charts that are being used for their growth."
Dr Prakash Shetty, head of nutrition planning at the UN's Food and Agriculture Organisation, said the new recommendations mean that daily energy intake for babies should be about 7% less than current levels.
"If you look at the requirements of these children who are exclusively breast-fed, their requirements of energy are much lower that those of formula fed infants."
Too much food, too little exercise
But babies are not the only ones who may have been being overfed.
Dr Shetty said the way calorie intake is measured should be changed.
Instead of just having two different amounts for men and women, people need to be assessed on how much energy they use, he said.
Someone who sits at a desk all day and does not exercise should consume fewer than 1,700 calories - significantly less than current recommendations of 2,000 calories for women and 2,500 for men.
Meanwhile, an individual who has an active job and does a lot of exercise like running marathons should be eating about 4,000 calories a day.
Dr Shetty said the amount of food we eat should be based on individuals energy expenditure.
He also recommended that we do more exercise.
"People must be physically very active and they must have activity levels which account for between 30 to 60 minutes of brisk walking everyday in order to maintain physical fitness and good health."