A study by the Schools Health Education Unit said 38% of surveyed girls in Year Six were not happy with their weight.
The figure increased as the girls developed, with almost two thirds of the Year 10s, aged 14 to 15, questioned wanting to lose weight. Only 32% of the age-group were happy with how they were.
The issue was not so prevalent with boys but the study did find that on average 31% of those in Years Six to 10 wanted to lose weight.
The report, based on data collected from more than 83,000 pupils in Years Six, Eight and 10 across the UK, revealed that almost a third of Year 10 girls had nothing to eat for breakfast on the day they were questioned. Of those who skipped breakfast, 24% said they also missed lunch the previous day.
Dr Laura Wyness, a senior nutrition scientist at the British Nutrition Foundation, said: "Popular media has a large influence on young people's body image, placing a great deal of pressure on obtaining the 'ideal' body shape. This often leads to young girls adopting unhealthy practices such as smoking, skipping meals (especially breakfast), severely reducing perceived fattening foods in their diet, such as red meat and dairy produce, which are important sources of protein, iron, zinc and calcium, and adopting very low energy (and therefore nutrient) diets.
"Having a healthy breakfast every day is important for providing essential nutrients. There is some evidence that eating breakfast may improve cognitive function. Breakfast clubs in schools have been found to have a small but positive impact on a selection of educational outcomes.
"Evidence suggests that eating breakfast may have a protective effect against becoming overweight or obese, however as the evidence is mainly from observational studies, causality should not be assumed based on these findings."
The report also said that as pupils get older, fewer eat fruit and vegetables daily despite Government recommendations that five portions should be consumed each day.
On average, 41% of the boys questioned did not eat fresh fruit, salads or vegetables on "most days", compared to 31% of girls. Of the girls and boys questioned from Year Six, 40% said they ate no protein "on most days". However, around a quarter enjoyed crisps, sweets or chocolate regularly.
The study also revealed that three quarters of girls aged 14 to 15 drank less than a litre of water on the day before they were questioned and 12% drank none at all.