Abstract and Introduction
Background: Obesity is a growing global public health problem. More than half the European and North American population is overweight or obese. Colon and rectum cancers are still the second leading cause of cancer death worldwide, and epidemiological data support an association between obesity and colorectal cancers (CRCs).
Aim: To review the literature on CRC epidemiology in obese subjects, assessing the effects of obesity, including childhood or maternal obesity, on CRC, diagnosis, management, and prognosis, and discussing targeted prophylactic measures.
Method: We searched PubMed for obesity/overweight/metabolic syndrome and CRC. Other key words included 'staging', 'screening', 'treatment', 'weight loss', 'bariatric surgery' and 'chemotherapy'.
Results: In Europe, about 11% of CRCs are attributed to overweight and obesity. Epidemiological data suggest that obesity is associated with a 30%–70% increased risk of colon cancer in men, the association being less consistent in women. Visceral fat or abdominal obesity seems to be of greater concern than subcutaneous fat obesity, and any 1 kg/m2 increase in body mass index confers more risk (hazard ratio 1.03). Obesity might increase the likelihood of recurrence or mortality of the primary cancer and may affect initial management, including accurate staging. The risk maybe confounded by different factors, including lower adherence to organised CRC screening programmes. It is unclear whether bariatric surgery helps reduce rectal cancer risk.
Conclusions: Despite a growing body of evidence linking obesity to CRC, many questions remain unanswered, including whether we should screen patients with obesity earlier or propose prophylactic bariatric surgery for certain patients with obesity.
The World Health Organization (WHO) defines being overweight and obese as abnormal or excessive fat accumulation in adipose tissue that may impair a person's health (https://www.who.int/mediacentre/factsheets/fs311/en/). Persons who are overweight have a body mass index (BMI, weight/[height in m]2) greater than or equal to 25 (BMI ≥25 kg/m2), and persons with obesity have a BMI greater than or equal to 30 (BMI ≥30 kg/m2).
Worldwide, obesity prevalence quadrupled for men and doubled for women between 1975 and 2016. Between 1975 and 2016, the absolute number of obese adults increased almost sevenfold, 100–671 million. In the United States, overall age-adjusted prevalence of obesity in 2014 was 37.7% (35.0% in men; 40.4% in women), trending towards a linear increase in women, but not in men over the previous decade. Obesity prevalence varies widely by region, occupation and socio-economic level. Obesity is three times as common in the United States (37.7%) as it is in Europe (12.8%). Recent data from China showed that from 1991 to 2015, prevalence of overweight increased from 4.6% to 21.1%, and obesity prevalence increased from 1.4% to 10.1%. Severe obesity increased from 0.2% to 4.0% (a relative increase of 1900.0%), as did overweight (relative increase of 358.7%) and obesity (relative increase of 621.4%). In US children and adolescents, obesity prevalence is 17.0% and has mainly stabilised since 2005, but epidemiological studies show an increase in other countries.
Although BMI correlates strongly with absolute adiposity, there is a distinction between accumulation of two types of fat (subcutaneous and visceral) that play different roles in metabolic syndrome and colorectal cancer (CRC).
Not all people with obesity are unhealthy, and only about two-thirds of patients with metabolic syndrome are obese.[9,10] Recommendations to measure waist circumference and waist-to-height or waist-to-hip ratios instead of BMI acknowledge that abdominal obesity plays a central role in metabolic syndrome, and that BMI might overestimate obesity. But no solid epidemiological or metabolic data support recommendations for specific waist circumference cut-offs to define abdominal obesity,[11,12] and the relationship between visceral fat and metabolic syndrome varies across ethnic groups.
CRC, the third most incident cancer worldwide, makes up 10.0% of total cases and is the second most common cause of cancer-related death (9.4% of all cancer deaths). In the United States, cumulative lifetime risk of developing a CRC is 5% in the general population. Obesity has been associated with 13 cancers, including CRC and liver cancer, with three cancers sites (endometrium, post-menopausal breast cancer and CRC) accounting for two-thirds of cancers attributable to excess BMI attributable cancers. About 3.6% of cancers (481,000 new cases a year) are attributable to excess BMI, his association being higher in countries with very high and high human development index (5.3% and 4.8%, respectively) than in low human development index countries (1.6%). Relative risk of colon cancer attributable to obesity is 1.24 for men overall, ranging between 1.04 and 1.13 across countries. Of the 1,347,000 new CRC cases diagnosed worldwide in 2012, in men 42,300/736,000 (5,8%) and in women 42,300/60,700 (7.0%) were attributable to high BMI. Similar estimates were reported for 384,402 incident cancers in France in 2015; of these 3380/43,000 incident CRC were attributed to obesity.
In this article, we analyse epidemiological data on CRC in obese subjects, discuss the effects of obesity on CRC management and prognosis and consider measures designed to reduce CRC risk in this population.
Aliment Pharmacol Ther. 2022;56(3):407-418. © 2022 Blackwell Publishing