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Could cancer be prevented through weight loss or the reversal of the mechanisms identified as increasing an obese individual’s cancer risk?
Theoretically, yes, of course.
There is a broad spectrum of information about obesity as a major cause of cancer. The question becomes which cancers are related to obesity, and the mechanisms for this vary from cancer to cancer. The ones that are most prominently discussed are hormone-related cancers, the most prominent of which are breast cancer and endometrial cancer. In these cancers, the relationship exists because obesity leads to increased fat, and fat contains enzymes which raise your estrogen levels. Theoretically, if you lose weight and lower hormone levels, then your risk should decline. The other major cancer that is associated with obesity is esophageal adenocarcinoma. That association exists because obesity increases esophageal reflux and gerd. I suppose if you remove obesity, you would have less gerd or reflux.
Studying the reversal of these factors as a means of cancer prevention is more challenging. Ideally, a study would show whether or not weight loss actually reduces risk; however, conducting a study like that would be difficult. It is almost impossible to imagine. There have been a few studies conducted where they have tracked people’s weight over time. In those studies, they have shown that people who lose weight have a decline in their cancer risk. You can’t be 100% sure of that because there may be confounding factors. Instead, most studies on weight loss and cancer risk look at intermediate markers. Researchers cannot look at cancer as an endpoint in their studies easily because cancer is so uncommon and such studies would require thousands of patients for years, and to require that half of them lose a significant amount of weight seems extraordinarily daunting.
Alfred Neugut, MD, PhD, is Myron M. Studner Professor of Cancer Research, Professor of Medicine and Epidemiology at Columbia University, Head of Cancer Prevention and Control for the Herbert Irving Comprehensive Cancer Center at Columbia, and Co-Director of the Cancer Prevention Center of New York Presbyterian Hospital.
Yes, there is some evidence to suggest this.
The evidence that could support it being a reversible problem is the example of metformin’s association with breast cancer risk. Some studies have shown that metformin decreases the risk of developing breast cancer, and it seems to be more beneficial when combined with chemotherapy as a treatment for breast cancer. This suggests that if you change the process, in this case by lowering insulin levels, increasing insulin sensitivity and possibly decreasing markers of inflammation, that you may be able to prevent breast cancer from occurring. This may suggest that there is potential for reversible disease mechanisms in this specific patient population; however, it may not be as simple as diet and weight loss, and will more likely involve medications. It is important to note that metformin has serious side effects and should be used judiciously.
Would weight loss, diet change or exercise be effective at reducing a woman’s risk for breast cancer? There has been evidence to support that women who had breast cancer and lost weight after their diagnosis had better outcomes than women who did not. In theory then, maintaining a healthy weight prior to diagnosis could reduce some women’s risk for the disease. However, additional mechanisms may be at work here and more studies are needed.
When looking at cancer prevention, I think it is important to look at all potential avenues to modify risk factors for cancer. There aren’t many factors that you can change, such as familial risk or genetic mutations, but the environmental issues you can modify, such as alcohol intake, diet and exercise, are the risk factors that we as clinicians should evaluate further to try to prevent disease. In people at high risk for cancer, if there are behaviors that can be altered to modify risk, we should attempt to do them. Conducting high-quality studies to gather concrete data and evidence may motivate people to change their behaviors such as keeping their weight down. Whether this can be achieved without medications could also be studied.
Katherine B. Lee, MD, is a Breast Specialist at the Cleveland Clinic Breast Center and is Assistant Professor of Medicine at the Cleveland Clinic Lerner College of Medicine of Case Western Reserve.