Our bodies are designed for physical activity. But today, it is optional. We sit when we travel, work, eat, or relax. While this may seem obvious, chronic physical inactivity coupled with overweight or obesity has been linked to biological circumstances that foster cancer risk.

The biology behind the risk

Adipose tissue is biologically active and influences hormone levels, metabolism, inflammation, and immune function.

Adipose tissue, for instance, becomes an essential source for estrogen in a female after menopause. Also, higher estrogen exposure may encourage growth of hormone-sensitive tissues in our body and lead to a greater risk of postmenopausal breast and endometrial cancer linked to obesity.

Insulin resistance and elevated levels of insulin and insulin-like growth factors have also been associated with obesity. Recent research has pointed out obesity’s association with chronic, low-grade inflammation and changes in inflammatory and metabolic signaling, which may create an environment more favourable for cancer development. It can influence cell growth and survival.

Hence, cancer risk involves hormonal, metabolic, inflammatory, and tissue-specific mechanisms, but with varying intensities across organs.

Which cancers are linked to excess body weight? 

The evidence is strong for a particular association between excess body weight and at least 13 cancer types, including the cancer of the endometrium, colon, rectum, kidney, liver, pancreas, gallbladder, ovaries, thyroid, meninges, and others.

But this does not prove that excess weight guarantees cancer. It means that, across populations, increasing fat increases the risk of cancer in the body.

Sedentary lifestyle: A modifiable risk factor

Although physical inactivity and obesity aren’t synonymous, doctors frequently link them together. Regular physical activity lowers the risk of colon, postmenopausal breast, and endometrial cancers, says Dr Sagar Panthi, a second-year resident in the Department of Conservative Dentistry and Endodontics at BP Koirala Institute of Health Sciences.

Exercise can impact cancer risk in many ways—promoting insulin sensitivity, reducing inflammation, controlling body fat and hormone levels, and affecting the immune and metabolic systems. Increased movement of the intestine can decrease the amount of time the gut lining is exposed to potentially harmful substances in colon cancer.

These benefits are felt without much weight loss. Physicians often note that a person with a normal BMI may still be afflicted with the metabolic effects of inactivity, and an overweight person may greatly benefit from cardiovascular and metabolic outcomes through a regular physical exercise program.

Why does the risk differ from one organ to another? 

The biological consequences of excess weight are not uniform. Over time, obesity can increase the risk for acid reflux, which can lead to the development of Barrett’s oesophagus and, in some cases, oesophageal adenocarcinoma.

According to the Medical Director of Rajiv Gandhi Cancer Institute & Research Centre (RGCIRC), Dr Vineet Talwar, excess body fat in the liver is closely linked to metabolic dysfunction-associated steatotic liver disease (MASLD). In some individuals, chronic metabolic stress, inflammation and liver damage may lead to fibrosis, cirrhosis and ultimately liver cancer.

In the gallbladder, obesity can also affect how cholesterol and bile are metabolised, potentially raising the risk of gallstones, which could lead to a risk of cancer.

Thus, there’s no single “obesity-to-cancer pathway”. Organs respond differently to the metabolic environment created by excess adiposity.

Beyond guilt: risk is not destiny

Genetics, hormones, sleep, medications, socioeconomic circumstances, food environments, physical surroundings and many other factors influence body weight. Obesity is a complex chronic disease, not simply a failure of willpower. This conversation should never become a conversation about blame.

Likewise, having excess body weight or being physically inactive does not mean that someone will develop cancer. And being physically active does not make a person immune to cancer. These are modifiable risk factors, not predictions of an individual’s future.

The practical answer: move more and sit less

Cancer prevention doesn’t mean one must be an athlete. Regular walking, doing housework, standing while on the phone and taking periodic breaks from sitting are easy strategies to add activity to daily life. Adults should aim for 150-300 minutes of moderate physical activity a week or 75-150 minutes of vigorous physical activity. Prolonged sitting should also be addressed.

It's not about perfection. The aim is to integrate “movement” into normal daily routine. But the battle against cancer doesn't end with exercise! Tobacco abstention, reducing alcohol intake, achieving a healthy body weight, and adhering to the appropriate age- and risk-based cancer screening guidelines are critical elements of cancer prevention.

Changing the environment in which our cells live 

Cancer develops over years, often through the accumulation of multiple biological changes. We cannot control every factor involved. But we can influence some of those factors which our cells experience during those years.

Our modern life has become extraordinarily comfortable. Cars have replaced walking. Elevators have replaced stairs. Screens have replaced many forms of physical activity. Perhaps the answer is not to reject that comfort, but to put physical activity back into it.

Stand up. Walk more. Sit less. Take the stairs. Move regularly. Every step may not prevent cancer. But over a lifetime, a more active body is a healthier biological environment, and that is something worth investing in.