Besides tobacco, obesity contributes to almost 40% of cancers, including kidney, liver, pancreatic, colorectal and post-menopausal breast and endometrial cancer. According to the Centre for Disease Control and Prevention (CDC), obesity is responsible for 20% of cancer-related deaths in women and 14% in men. Surely this should mean that by reducing obesity rates, we could bring down the risk of cancer in many at-risk individuals. In Singapore, bariatric surgery is an effective strategy for individuals with morbid obesity who fail to lose weight despite a supervised diet and exercise program.
But does bariatric surgery, that brings about weight loss, have potential cancer prevention effects? So far, the literature demonstrates a positive link mostly in post-menopausal endometrial and breast cancers only. Why is this so? Let’s find out more.
How does obesity promote cancer?
Obesity promotes and accelerates cancer growth through multiple mechanisms. On the surface, adipose tissue exists as body fat, but did you know it functions as a mediator of multiple inflammatory and metabolic signals as well? What this means is that expanding adipose tissue or excessive body fat increases the secretion of adipokines like leptin and resistin. These adipose-specific proteins have been shown to stimulate tumour growth.
The enzyme aromatase, which converts androgens to oestrogen and resides in adipose tissue, is increased in obesity. Further, obesity and obesogenic diets cause changes in intestinal microbiota and epigenetics, inducing cancer-promoting effects.
Lifestyle modifications to achieve intentional weight loss in morbidly obese patients have been shown to normalise cancer risk mechanisms, including estrogens and insulins. Weight loss is achieved through a decrease in food intake and increase in energy expenditure, and so far, bariatric surgery has been shown to be the most effective way to achieve significant weight loss.
Types of bariatric surgery in Singapore
| Procedure | Pros | Cons |
| Sleeve gastrectomy | Rapid and significant weight loss of up to 70% Improvement of most cardiovascular disorders like hypertension No significant nutritional deficiencies associated | Irreversible Staple line leaks can occur Associated with GERD |
| Roux-en-Y gastric bypass | Steady and significant weight loss Corrects all cardiovascular complications from obesity Sustained long term weight loss, most patients maintain 50% of their initial weight loss | Irreversible Dumping syndrome when eating food high in sugar and fat Malabsorption of vitamins and minerals Chance of developing gallstones due to rapid weight loss |
| Gastric banding | Reversible Least invasive process Fastest recovery time Safest option for morbidly obese patients or those with history of abdominal surgery Lowest risk of deficiencies | Weight loss is lower Potential complications include band slippage and port erosion |
| Duodenal switch | Used for extremely obese patients (BMI > 50) Weight loss of up to 80% Corrects obesity-related complications Patients can eat normally after recovery | Most technically challenging bariatric surgery Highest rate of post-surgery complications |
| Omega-loop gastric bypass | Weight loss of up to 80% Corrects all obesity-related complications | Irreversible Liver enzyme elevation Malabsorption of vitamins and minerals May develop GERD |
I’ve written articles on gastric banding, gastric bypass and gastric sleeve gastrectomy in detail, as well as the differences between a gastric bypass and sleeve gastrectomy. You may check them out for more information on the respective bariatric surgeries.
Bariatric surgery and cancer prevention in Singapore
A 2019 study on a bariatric surgery cohort found that those who lost 20-34.9% of their bodyweight had a 56% reduced risk of developing cancer. In another recent study, bariatric surgery reduced cancer risk by about 46% in women while there was no cancer risk reduction observed in men. Does this mean that there are sex differences in cancer-risk benefits? No— it just means that it is impossible to draw any conclusions due to the low inclusion of males who undergo bariatric surgery. About 80% of patients who undergo bariatric surgery are females.
Nevertheless, bariatric surgery has been shown to successfully achieve weight loss, and the rapid metabolic changes —especially lowered insulin levels and decreased T2DM— could reduce major cancer promoting factors. While more research needs to be done, I think we should not forget the main intention of bariatric surgery, which is to lose weight for a healthier life. Going in with the mindset of purely lowering cancer risk would not be the correct mindset.
It is important that patients undergoing bariatric surgery do not expect their cancer risk to be eliminated or reduced beyond the non-obese, normal BMI population.
References
- Bruno, D. S., & Berger, N. A. (2020). Impact of bariatric surgery on cancer risk reduction. Annals of translational medicine, 8(Suppl 1), S13. https://doi.org/10.21037/atm.2019.09.26
- Singh, P., Subramanian, A., Adderley, N., Gokhale, K., Singhal, R., Bellary, S., Nirantharakumar, K., & Tahrani, A. A. (2020). Impact of bariatric surgery on cardiovascular outcomes and mortality: a population-based cohort study. The British journal of surgery, 107(4), 432–442. https://doi.org/10.1002/bjs.11433
