Does obesity affect cancer survival?
Parkway Cancer Centre’s Dr Tan Wu Meng looks at possible links between cancer and obesity.
Obesity and being overweight have been known as risk factors for all kinds of illnesses. In recent years, however, there has been renewed interest in the relationship between obesity and cancer.
The body mass index (BMI) is a simple index that is commonly used to check whether adults are overweight or obese. It is calculated as a person’s weight in kilograms, divided by the square of his/her height in metres (kg/m2
According to the World Health Organization, a person is overweight if his BMI is 25 or greater, and obese if it is 30 or more.
The role of obesity in surviving cancer can be challenging to study. If the effect of obesity is subtle, its impact might be statistically hard to detect if a survey covers a small number of patients.
Some researchers have used meta-analysis, a statistical method in which many clinical studies are grouped together, to build a bigger pool of data.
At the American Society of Clinical Oncology’s annual meeting in 2014, a large meta-analysis of 80,000 patients with early stage breast cancer was presented.
This study found that for pre-menopausal or near-menopausal women whose cancers were positive for the oestrogen-receptor-positive (or ER+), a higher BMI appeared to indicate higher mortality among those with breast cancer.
A similar research has been conducted in prostate cancer
. Another large meta-analysis looked at patient data across multiple prostate cancer studies, both in cancer-free men as well as men already diagnosed with prostate cancer. Among the 1,263,483 initially cancer-free men studied, the meta-analysis found that a 5 kg/m2
increase in BMI was associated with a 15 per cent higher risk of dying of prostate cancer.
This study also looked at 18,203 patients who had been diagnosed with prostate cancer.
The researchers found that a 5 kg/m2
increase in BMI correlated to a 21 per cent increased risk of biochemical recurrence, which is when the level of PSA (prostate-specific antigen) increases despite treatment being given for the prostate cancer.
Why would obesity affect mortality rates in prostate cancer and ER+ breast cancer?
One possibility is that obesity affects the mix of hormones in the body. Another explanation is that patients, who are physically less fit to begin with, may also be more susceptible to the impact of cancer and the side effects of therapy.
We do not fully understand how obesity influences the outcome of breast and prostate cancers. But we know this for sure: It is never too early to take up a healthy lifestyle – eat in moderation and exercise regularly.
Eat well, keep fit, fight cancer
Some studies have found that for some cancers, being overweight at diagnosis has been associated with cancer-related death, although this relationship is still being researched. By keeping fit, you can stay in better shape to fight cancer.
- Maintain a healthy and balanced diet as part of the fight against cancer.
- Include vegetables in your meals, and eat enough fruit and vegetables each day.
- Cut down on saturated fat and sugar.
- Balance your energy intake and energy expenditure. Reduce your fat intake to less than 30 per cent of total energy intake by removing the fatty part of meat. Use vegetable oil instead of animal oil. Boil, steam or bake, rather than fry, and limit your consumption of food that has lots of saturated fats, such as fatty meat or ice cream.
- Keep active – it will help you maintain a healthy weight.