Many studies have reported a slight increased risk of pancreatic cancer among overweight and obese individuals. Waist circumference may be a particularly important factor in the association of overweight and obesity with pancreatic cancer.
7 What is known about the relationship between obesity and thyroid cancer?
Increasing weight has been found to be associated with an increase in the risk of thyroid cancer. It is unclear what the mechanism might be.
8 What is known about the relationship between obesity and gallbladder cancer?
The risk of gallbladder cancer increases with increasing BMI. The increase in risk may be due to the higher frequency of gallstones, a strong risk factor for gallbladder cancer, in obese individuals.
9 What is known about the relationship between obesity and other cancers?
The relationship between obesity and prostate cancer has been studied extensively. The results of individual studies do not suggest a consistent association between obesity and prostate cancer. However, when the data from multiple studies are pooled, analyses show that obesity may be associated with a very slight increase in the risk of prostate cancer.
In addition, several studies have found that obese men have a higher risk of aggressive prostate cancer than men of healthy weight. Generally, risk of prostate cancer has been linked to levels of certain hormones and growth factors, especially IGF-1.
Some studies have shown a weak association between increasing BMI and risk of ovarian cancer, especially in premenopausal women, although other studies have not found an association. As with some other cancers, an association between ovarian cancer and obesity may reflect increased levels of estrogens.
Some evidence links obesity to liver cancer and to some types of lymphoma and leukemia, but additional studies is needed to confirm these associations.
10 Does avoiding weight gain or losing weight decrease the risk of cancer?
The most conclusive way to test whether avoiding weight gain or losing weight will decrease the risk of cancer is through a controlled clinical trial. A number of weight loss trials have demonstrated that people can lose weight and that losing weight reduces their risk of developing chronic diseases, such as diabetes, while improving their risk factors for cardiovascular disease.
However, previous trials and the results have demonstrated that it would not be feasible to conduct a weight loss trial of cancer prevention. The reason is that the effect of weight loss on the prevention of other chronic diseases would be demonstrated—and the trial consequently stopped so that the public could be informed of the benefits—before the effect on the prevention of cancer would become evident.
Therefore, most data about whether losing weight or avoiding weight gain prevents cancer come mainly from cohort and case-control studies. Data from these types of studies, called observational studies, can be difficult to interpret because people who lose weight or avoid weight gain may be different in other ways from people who do not, just as obese people may differ from lean people in other ways than BMI.
That is, it is possible that these other differences explain their different cancer risk.
Nevertheless, many observational studies have shown that people who have a lower weight gain during adulthood have a lower risk of:
a) Colon cancer
b) Breast cancer (after menopause)
c) Endometrial cancer
A more limited number of observational studies have examined the relationship between weight loss and cancer risk, and a few have found decreased risks of breast cancer and colon cancer among people who have lost weight. However, most of these studies have not been able to evaluate whether the weight loss was intentional or related to underlying health problems.
Stronger evidence comes from studies of patients who have undergone bariatric surgery to lose weight. Obese people who have bariatric surgery appear to have lower rates of obesity-related cancers than obese people who did not have bariatric surgery. It is important to note that whereas most lifestyle weight loss interventions result in weight losses of 7-10 percent of body weight, weight loss from bariatric surgery combined with lifestyle changes generally results in weight loss of 30 percent.
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