Cancer Care

Let’s talk obesity and cancer

February 5, 2021 Word for Word Media 0Comment

Prof Gita Naidu shares evidence that obesity is a significant risk factor for cancer development, cancer progression, and a patient’s response to therapy.

In 2016, more than 1,9 billion adults aged 18 years and older were overweight, 39% were males and 40% females. Of these, over 650 million adults were obese, of which 11% were male and 15% female. The worldwide prevalence of obesity nearly tripled between 1975 and 2016. 

During the same period, an estimated 41 million children under the age of five years were overweight or obese, and 340 million children and adolescents, aged 5 to 19, were overweight or obese. The prevalence of overweight and obesity among children and adolescents aged 5 to 19 has risen dramatically from just 4% in 1975 to just over 18% in 2016. The rise has occurred similarly among both boys and girls: in 2016 18% of girls and 19% of boys were overweight.

Once considered a high-income country problem, overweight and obesity are now also increasing in low- and middle-income countries, particularly in urban settings. 

In Africa, the number of overweight children under five years of age has increased by nearly 50% since 2000. Nearly half of the children under five who were overweight or obese in 2016, lived in Asia.

Researchers found that as of 2014, 10,8% of men and 14,9% of women worldwide were obese i.e. with a BMI of 30 or higher. Another 2,3% of the world’s men were considered severely obese, compared to 5% of women, while 0,64% of men and 1,6% of women were morbidly obese. 

Drivers of the obesity pandemic

  • An overall rise in caloric intake.
  • Increased consumption of high carbohydrate beverages and dietary fat.
  • Low levels of physical activity. 
  • Significant but poorly understood role of genetic factors, but this accounts for less than 5%..

 SA context

A survey in SA, conducted during 2016, found 20,3% of males aged 15 years and older were overweight while 11% were obese. Similarly, 26,6% of females aged 15 years and over were overweight while 41% were obese.

Pathophysiology of obesity and cancer

Obesity is strongly associated with changes in the physiological function of adipose (fat tissue), leading to insulin resistance, chronic inflammation, and altered secretion of adipokines. Several of these factors, such as insulin resistance, increased levels of leptin, plasminogen activator inhibitor-1, and endogenous sex steroids, decreased levels of adiponectin, and chronic inflammation, are involved in carcinogenesis and cancer progression.

A robust body of evidence demonstrates that many cancer cells, in contrast to normal cells, subsist primarily (although not exclusively) on glucose metabolism via aerobic glycolysis, regardless of oxygen availability. This phenomenon is known as the Warburg effect. 

Obese people often have chronic low levels of inflammation, which can, over time, cause DNA damage that leads to cancer. Overweight and obese individuals are more likely than individuals of normal weight to have conditions or disorders that are linked to or that cause chronic local inflammation which have been identified as risk factors for certain cancers.

Chronic local inflammation induced by gastro-oesophageal reflux is a likely cause of oesophageal adenocarcinoma. Obesity is a risk factor for gallstones, a condition characterised by chronic gallbladder inflammation, and a history of gallstones is a strong risk factor for gallbladder cancer. Chronic ulcerative colitis (a chronic inflammatory condition) and chronic hepatitis (liver inflammation) are risk factors for different types of liver cancers.

Fat tissue produces excess amounts of oestrogen, high levels of which have been associated with increased risks of breast, endometrial, and ovarian cancers. Fat cells may also have direct and indirect effects on other cell growth regulators, thus promoting cancer development. 


A population-based study using BMI cancer incidence data from the GLOBOCAN project estimated that, in 2012 in the United States, about 28 000 new cases of cancer in men (3,5%) and 72 000 in women (9,5%) were due to overweight or obesity. 

The percentage of cases attributed to overweight or obesity varied widely for different cancer types but was as high as 54% for gallbladder cancer in women and 44% for oesophageal adenocarcinoma in men.

A 2016 study summarising worldwide estimates of the fractions of different cancers attributable to overweight and obesity reported that, compared with other countries, the United States had the highest fractions attributable to overweight and obesity for colorectal and pancreatic cancer, and post-menopausal breast cancer.

Cancer survivorship

Many observational studies have provided consistent evidence that people who have lower weight gain during adulthood have lower risks of colon cancer, kidney cancer, and, for postmenopausal women, breast, endometrial, and ovarian cancers.  

Most of the evidence about obesity in cancer survivors comes from people who were diagnosed with breast, prostate, or colorectal cancer. 

Research indicates that obesity may worsen several aspects of cancer survivorship including quality of life, cancer recurrence, cancer progression, and overall survival. 

Obesity is associated with increased risks of treatment-related lymphoedema in breast cancer survivors and incontinence in prostate cancer survivors treated with radical prostatectomy. In a large clinical trial of patients with rectal cancer, those with a higher baseline BMI (particularly men) had an increased risk of local recurrence. Death from multiple myeloma is 50% more likely for people at the highest levels of obesity compared with people at normal weight.

Survivors of childhood cancer and obesity

Childhood cancer survivors of acute lymphoblastic leukaemia or those who received radiation, more specifically brain, abdominal, and total body irradiation, are at highest for obesity. 

The use of steroids for the treatment of childhood acute lymphoblastic leukaemia increases the risk of survivors. 

Damage to the pituitary gland and hypothalamus during radiation may result in obesity as these organs regulate the metabolic processes in our bodies and may result in over-eating and weight gain. Whether obesity is linked to cancer treatment itself or poor nutritional choices and lack of exercise, it still puts our childhood cancer survivors at an increased risk of cancer in adulthood.

Global burden of cancer attributable to a high BMI

A population-based study, carried out in the UK, estimated 481 000 or 3,6% of all new cancers (or 12,8% of all high BMI-related cancers) in adults in 2012 were attributable to a high BMI. 136 000 (1,9%) of all new cancers in men and 345 000 (5,4%) in women were attributable to high BMI. 

Another study investigated the relationship between BMI and the risk of 22 specific cancers. It was population-based cohort study of 5,24 million adults in the UK in 2014. 166 955 BMI-related cancers were recorded in 24 million individuals and a high BMI was associated with 17 of 22 cancers. 

Each 5 kg/m² increase in BMI was linearly associated with the following cancers in order of frequency:

  • Uterus 
  • Gallbladder 
  • Kidney 
  • Cervix 
  • Thyroid 
  • Leukaemia 

BMI was positively associated with cancers of the:

  • Liver 
  • Colon  
  • Ovarian 
  • Postmenopausal breast cancers  


Divide weight in kilograms by height in m2. For example, if you are 1,65m tall and weigh 85kg: weight/height squared = 85/1,65 x 1,65 = 85/2,72 = 31,25. 

Normal BMI: 18.5 -24.9

Overweight BMI: 25–29.9 

Obesity BMI: >30 

13 cancers are associated with overweight and obesity

Preventable causes of cancer

  • Tobacco – 30%
  • Diet – 30%
  • Obesity – 15%
  • Infection – 7%
  • Physical inactivity – 5%
  • Alcohol – 4%
  • Radiation (solar & ionizing) – 3%
  • Occupational – 3%
  • Pollution, medical procedures, sexual and reproductive behaviour, food additives, industrial products – all together 3%


It’s critical to identify innovative ways to curb the negative effect of the increasing obesity pandemic using public health measures, food taxes, education and policies aimed at lifestyle modifications.

DProfessor Gita Naidu MBChB, FC (Paediatrics), MMed (Paediatrics), PhD is the Head of Paediatric Oncology, Chris Hani Baragwanath Academic Hospital, University of the Witwatersrand and the Chair of South African Children’s Cancer Study Group.

MEET THE EXPERT – Prof Gita Naidu

Professor Gita Naidu MBChB, FC (Paediatrics), MMed (Paediatrics), PhDis the Head of Paediatric Oncology, Chris Hani Baragwanath Academic Hospital,University of the Witwatersrand and the Chair of South African Children’sCancer Study Group.

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