text: Researchers followed nearly 240,000 Swedish men for 35 years.
  The analysis, published in the journal Gut, showed overweight teenagers went on to have twice the risk of bowel cancer. The figures were even higher in obese teens.
  The World Cancer Research Fund said the link between obesity and cancer was "strong".
  Bowel cancer is the third most common cancer in the world, with nearly 1.4 million new cases each year.
  Processed red meat and abdominal fat have been linked to the disease.
  The participants in the study were aged between 16 and 20 at the start.
  The overwhelming majority were a normal weight, but 6.5% were overweight and 1% were obese.
  There were 855 cases of colorectal cancer in the study.
  However, the results showed not all weights were affected equally.
  Those who were obese were 2.38 times more likely to have developed a bowel tumour.
  The study, led by Orebro University Hospital in Sweden and Harvard University, said: "Late adolescence marks the transition from childhood to adulthood and is a period of accelerated growth, especially among men, thus this period may represent a critical window."
  "It is important that we understand the role of exposures in childhood and adolescence in the development of colorectal cancer.
  "In fact, the strong association observed between adolescent obesity and early-to-mid-life colorectal cancer, coupled with the increasing prevalence of adolescent obesity, may shed light on the increase in colorectal cancer incidence among young adults," he added.
  Rachel Thompson, from the World Cancer Research Fund, said the evidence suggested that obesity was a risk factor for bowel cancer.
  "This finding is interesting because it gives an indication that bowel cancer risk might be affected by our lifestyle habits throughout the life course," she said.
  "In some ways, research into the relationship between factors like obesity and cancer risk is still in its infancy.
  "It will be interesting to see if further research emerges in the future to back up the apparent relationship between body fatness in youth and later-life cancer risk."
target: Being overweight in adolescence is linked to a greater risk of bowel cancer later in life, a study suggests.