In cancers of reproductive organs, such as endometrial and ovarian cancers, obesity may also act through hormonal mechanisms. Adipose, or fatty, tissue is estrogenic; and estrogen is a powerful hormone, acting to increase cell proliferation and inhibit cell death in the endometrial tissue. This combination promotes cancer growth.
Finally, obesity can also place mechanical stress on the body that increases cancer risk. For example, obesity increases the risk of hypertension (high blood pressure), an established risk factor for kidney cancer.
Regardless of the mechanism (or mechanisms) at play, it is clear that being overweight and obese increase cancer risk. We also know that changing weight can change cancer risk. Gaining weight from early adulthood to later in life, even modestly, increases cancer risk. For example, in a Canadian study, men who gained 21 kg (46.2 lbs) or more since age 20 were at a 60% increased risk of colorectal cancer as compared to men who had gained 1-5 kg (2.2 to 11 lbs). Another study of men and women found that, compared to those who had remained BMI-stable, those who increased their BMI from age 30 or 50 to cancer diagnosis were at a 25-35% higher risk of colorectal cancer. Similarly, a study of US nurses found that women who lost 10 kg (22 lbs) or more after menopause, and kept it off, saw a 50% reduction in breast cancer risk. Losing 10 kg might seem like an impossible task for some women, but that same study found that women losing just 2 kg (4.4 lbs) still saw their risk go down.
Obesity causes a substantial proportion of all cancers, and emerging evidence suggests adult weight loss reduces cancer risk. To maintain a healthy weight, focus on eating a diet rich in fruits, vegetables and whole grains, avoid sugary beverages and junk food, and build physical activity into your daily life. These factors not only help in maintaining a healthy weight, but we have evidence that they protect against cancer on their own. For example, people who are physically active have a significantly lower risk of several cancers, including colon, breast and endometrial. Fruits, vegetables and whole grains contain important compounds, like folate, which we’ve seen in some studies to lower pancreatic cancer risk. It might sound cliché, but increasing physical activity and avoiding weight gain are, and have always been, important tools in the fight against cancer.