Even so, another cancer expert who reviewed the finding recommended "taking it with a grain of salt and a little bit of hesitation."
"I would say overall the evidence appears [to show] there is a reduction in risk," said Lauren Teras, director of hematologic cancer research at the American Cancer Society. "It's just hard to say for certain."
Even the researchers suggest that the conclusion should be viewed with care, since the studies they reviewed differed in the way they were conducted, potentially affecting results. Also, the review was not designed to determine a cause-and-effect link.
How to explain the apparent association between obesity and cancer?
"I think there is some good evidence that hormones play a role," Teras said. For instance, fat tissue is the largest source of estrogen in women past menopause, and that is thought to be linked with the type of breast cancer that needs estrogen to grow.
Another possible connection, she said, is inflammation. As people gain more and more weight, they have an increase in inflammation, and that may help tumors grow and spread.
"We're not sure if the obesity causes the cancer," Stein said, "but it may promote it."
Teras offered one more caveat: "Weight-loss surgery, like any surgery, is not without risks. The risks and benefits should be weighed with a person's individual doctor."