A new study from Sweden suggests that obesity — being grossly overweight — raises a person's risk of developing three more kinds of cancer than earlier thought — lymphoma (immune system cell cancer), and cancers of the larynx (voice box) and small intestine.

"Obesity is associated with more forms of cancer than previously reported," the researchers write in Cancer Causes and Control (Vol. 12, No 1: 13-21)

This new finding is particularly disturbing to health scientists because obesity is becoming more common throughout the world. According to the article, more than 30% of older Americans are obese, making this an important public health problem.

The researchers, led by Alicia Wolk of the Karolinska Institute in Stockholm, Sweden, tracked 28,129 patients who were obese when they were released from Swedish hospitals in the years 1965 through 1993, and noted any cancers they developed as much as 29 years later.

They found that compared to those not obese, people who were obese were more than twice as likely to develop cancer of the larynx , almost three times more likely to develop cancer of the small intestine, and 1.4 times as likely to develop lymphoma.

The study also confirmed earlier data that showed obese people are more likely than others to develop cancers of the colon; gallbladder; cervix; ovary; brain; connective tissues; and, to develop endometrial cancer.

"One reason people become obese is they consume too much fat, too many calories, and too little fiber," notes Colleen Doyle, MS, RD, director of nutrition and physical activity for the American Cancer Society (ACS).

Doyle says such a diet can contribute to cancer risk even without obesity, and will also likely be low in fruits and vegetables that contain numerous natural substances, such as antioxidants, that help neutralize cancer-causing chemicals.

Fiber helps reduce colon cancer risk, Doyle notes, by speeding the absorption of nutrients and the passage of food through the intestines, so that cancer-causing substances formed there aren't in contact as long with tissue that could be damaged by them.

Doyle also notes that as a woman adds excess weight, she adds more fat, and fat produces excess estrogen, which is known to increase the risk of cancers of the breast and endometrium.

In men, obesity may raise risk of prostate cancer by interfering with proper regulation of the male sex hormone testosterone, and there are other links between obesity and increased cancer risk that scientists can observe, but not yet fully explain, Doyle notes.

The researchers note that another reason many people are obese is that they don't engage in much physical activity.

Doyle notes that physical inactivity raises the chances a person will develop colon cancer and breast cancer, and the Swedish researchers say it may also raise the risk of cancers of the endometrium and prostate.

"Most cancers are due to lifestyle choices such as diet, physical activity, and smoking," says Doyle.

Doyle says about one-third of cancer deaths in the US every year could be avoided if people applied the ACS guidelines on nutrition and engaged in regular physical activity as recommended.

Adults should do something for at least a half hour every day that takes as much effort as a brisk walk, Doyle tells ACS News Today.

And children and teens should be that active at least an hour every day, she adds.

Doyle notes that the ACS and other community-based organizations are increasingly alerting the community to the importance of diet and activity in preventing cancer.

"As more and more people experience how great a good diet and some regular activity makes them feel on a daily basis, we may see greater fitness become a growing trend, and obesity — and the cancers related to it — occuring less often," Doyle concludes.