The more fat cells a person has, the more leptin will be in their bloodstream.
The San Diego team wanted to find further evidence of the link by watching what happened to human cancer cells exposed to the hormone.
In a laboratory, they added the hormone to different varieties of cancer cell.
Growth was stimulated in all the cell lines – and in two out of three tested, the hormone also hampered the usual process of programmed death that allows the body to replace normal cells, but which often malfunctions in cancers.
The results, said lead investigator Kim Barrett, may explain why obese people have unusually high risks of developing colon cancer, and could help guide drug development. Left unsaid, but hopefully intended, is the insight the findings provide into the importance of eating well.