Lifestyle habits can have lingering health effects. You likely know that if you sunbathed for many years as a teen and young adult and then stopped worshipping the sun, you still have a higher risk of developing sun-related skin cancers. If you smoked for a significant period and then stopped, your pack year history remains and is linked to risk of developing COPD or lung cancer. It may however surprise you to know that if you were diagnosed with obesity or if you’ve carried significant excess weight for a period of time, but lose the weight and maintain that weight loss, you may still have an elevated risk for cancer.
What is the relationship between obesity and cancer risks?
The relationship between being obese and increased risk of developing several different cancers has been established by numerous research studies. Gaining weight or being obese causes changes in the body that link to the increased risk.
The changes that seem to explain the link include:
- Obesity is linked to increased levels of insulin and insulin growth factor-1 (IGF-1), which may nudge certain cancers
- Obesity is linked to chronic, low level inflammation which is linked to increased risk of several conditions including cancers
- Obesity causes elevated amounts of estrogen (secreted by fat cells) which can drive genesis of certain cancers like breast and endometrial cancer
- Fat cells have been implicated in the processed that regulate cancer cell growth
The types of cancers linked to being overweight or diagnosed with obesity include: breast, colorectal, uterine, kidney, head and neck, esophageal, pancreatic, endometrial, prostate, gall bladder and thyroid.
Addressing obesity-related cancer risks
If you lose weight you may be able to relieve a partial health burden in terms of the level of risk, but what’s clear is that the obesity-linked biological changes remain even after weight is lost, so overall risk of associated diseases like certain cancers remain. That means that the risk of developing cancer persists.
Researchers at the University of North Carolina Lineberger Comprehensive Cancer Center are actively working on ways to limit this lingering risk, by looking for ways to reverse obesity-linked changes in the body that promote cancer growth. They specifically address the reality that the science community may have approached weight loss a bit too simplistically – just because weight gain raises the risk of cancer doesn’t translate into – “lose weight and the problem is solved.”
The researchers are focusing on the epigenetic, metabolic, and inflammatory changes that persist after excess weight is lost. In one preclinical study presented at the 2018 American Association for Cancer Research (AACR) Annual Meeting, a study on diets showed that when examining the risk of aggressive basal-like breast cancer, mice who lost weight on a low fat diet did not reduce the lingering risk of this cancer, but severe weight loss accomplished by a “very low calorie or severe diet” did appear to break the obesity–cancer link. Researchers have further theorized that pace of weight loss and amount of weight loss may both work to diminish linked risk.
Findings from another study presented at the AACR meeting looked at pace and amount of weight loss and impact on risk of developing HER2-positive breast cancer. Specifically, the study looked at the impact of severe dramatic weight loss on a protein (P21) that seems to instigate HER2-overexpressing breast cancer cells. Preliminary results were promising.
Pancreatic cancer has few identified risk factors, but it is linked to obesity and it’s a cancer that has a high mortality rate. One study examined how weight loss can affect certain metabolic pathways and help to reduce pancreatic adenocarcinoma cell growth.
Low calorie diets and cancer growth
Researchers believe that starving certain cells may be an effective mechanism that can reduce or remove the cancer-post obesity link. Growth-suppressive effects of calorie restriction appears to be the frontier of research that may provide solutions for people who are no longer obese but still have risks for cancer. Inhibiting insulin-growth factor signaling appears to be another pathway to limiting cancer risks.
Very low-calorie diets (VLCD) have been around for decades and have been used to treat obesity. These diets are typically doctor-supervised and meant to treat those individuals diagnosed with a BMI greater than 30; more often to treat those with a BMI over 35 or 40.
Long-term maintenance of weight loss achieved with VLCD is not very successful. These diets typically hover around 800 calories, though in the face of morbid obesity caloric intake in an in-hospital setting can go lower.
Bariatric surgery aims to limit calorie intake dramatically over a period, to achieve rapid, dramatic weight loss. That feature may have relevance in this discussion of reducing post obesity risk factors for cancer.
It should be noted that VLCD can also help to reverse diabetes complications while having few negative influences on the heart. Given the numerous studies discussed above, it seems clear that aspects of weight loss including amount and pace of loss, may help to drive therapeutic approaches that may help to sever the link between the lasting impact of even obesity in remission and risk of cancer.