There is strong evidence that obesity may be associated with an increased risk of a wide range of cancer types including liver, colorectal, gastro-esophageal, gastric, thyroid, bladder, kidney, pancreatic, ovarian, lung, breast, endometrial and gallbladder cancers. Obesity/overweight is characterized by chronic low-grade inflammation and insulin resistance, which links it to cancer. Use a BMI calculator to constantly monitor your body-mass index (BMI) and ensure that you maintain a healthy weight by following a diet containing whole grains, fruits, vegetables and beans, and doing regular exercises.
Obesity/Over-weight and Body Mass Index (BMI)
Obesity/overweight was once considered as a main health issue found in the high-income countries, however, recently the number of such cases in the urban areas of both low-income and middle-income countries has also tremendously increased. The main reason for obesity and overweight in many people is that they eat more calories than they burn through activity. When the amount of calorie intake is the same as the amount of calories burnt, a steady weight is maintained.
There are several factors which contribute to overweight and obesity.
Some of these are:
- Following unhealthy diet
- Lack of physical activity, movement and exercise
- Having hormonal problems resulting in health conditions such as underactive thyroid, Cushing Syndrome and Polycystic Ovary Syndrome
- Having a family history of overweight or obesity
- Taking Medications such as corticosteroids, antidepressants, and seizure medicines
Body mass index : Body mass index (BMI) is a way of measuring whether your weight is healthy in regards to your height. Even though BMI mostly correlates with total body fat, it is not a direct measurement of body fat and should be considered as an indicator of whether you have a healthy weight.
Calculating BMI is simple. Many BMI calculators are also available online. The logic used by these BMI calculators is simple. Divide your weight by the square of your height. The resulting number is used to categorize whether you are underweight, have a normal weight, overweight or obese.
- BMI less than 18.5 indicates that you are underweight.
- BMI from 18.5 to <25 indicates that your weight is normal.
- BMI from 25.0 to <30 indicates that you are overweight.
- BMI of 30.0 and above indicates that you are obese.
Foods and Obesity
Following an unhealthy diet or taking unhealthy foods in large quantities leads to overweight and obesity. Some of the foods which can lead to weight gain are:
- Fast foods and highly processed foods
- Red meats
- Processed meats
- Fried foods including potato crisps,chips, fried meat etc.
- Excess intake of starchy potatoes
- Sugary drinks and beverages
- Alcohol consumption
Some of the foods which may help to stay away from obesity and overweight are:
- Whole grains
- Legumes, beans etc
- Nuts including almonds and walnuts
- Flaxseed oil
- Green tea
Along with taking the right foods, taking regular exercise is inevitable.
Health Issues Associated with Obesity/Over-weight
Obesity/over-weight is one of the major factors which increases the burden of different types of diseases in the world.
Some of the health conditions and outcomes associated with obesity are:
- Difficulty in physical functioning
- High blood pressure
- High cholesterol
- Different Types of Cancers
- Type 2 diabetes
- Heart diseases
- Gallbladder disease
- Depression, anxiety and other mental disorders
- Breathing problems
- Sleep disorders
- Low quality of life
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Obesity and Cancer
There is strong evidence that those who are obese or overweight have an increased risk of developing different types of cancers. Some of the studies and meta-analyses which evaluated the association between obesity and different types of cancers are collated below.
Association of Waist Circumference with Liver Cancer Risk
In a recent meta-analysis published in 2020, few researchers from Iran, Ireland, Qatar and China evaluated the association between waist circumference and liver cancer risk. The data for the analysis was obtained from 5 articles published between 2013 and 2019 which included 2,547,188 participants, through a comprehensive systematic literature search in MEDLINE/PubMed, Web of Science, Scopus, and Cochrane databases. (Jamal Rahmani et al, Liver Cancer., 2020)
Waist circumference is an indicator of abdominal fat and obesity. The meta-analysis concluded that greater waist circumference is a significant risk factor for liver cancer risk.
Association with Colorectal Cancer Risk
Study by Researchers in China
In 2017, a meta-analysis was performed by the researchers in China to study whether colorectal cancer risk was associated with abdominal obesity as measured by waist circumference and waist-to-hip ratio. They used 19 studies from 18 articles obtained through literature search in Pubmed and Embase databases, which included 12,837 colorectal cancer cases among 1,343,560 participants. (Yunlong Dong et al, Biosci Rep., 2017)
The study found that greater waist circumference and waist-to-hip ratio were significantly associated with an increased risk of colorectal cancer, colon cancer and rectal cancer. Findings from this study provide evidence that abdominal obesity may play an important role in the development of colorectal cancer.
BMI, Waist Circumference, Hip Circumference, Waist-to-hip ratio and Colorectal Cancer : Europe Study
In a meta-analysis of 7 cohort studies in Europe participating in the CHANCES consortium including 18,668 men and 24,751 women with a mean age of 62 and 63 years, the researchers studied the association of general obesity measured by body mass index (BMI) and body fat distribution measured by waist circumference, hip circumference, and waist-to-hip ratio, with the risk of different cancers. During a mean follow-up period of 12 years, a total of 1656 incidence of obesity-related cancers including postmenopausal breast, colorectum, lower oesophagus, cardia stomach, liver, gallbladder, pancreas, endometrium, ovary, and kidney cancers were reported. (Heinz Freisling et al, Br J Cancer., 2017)
The study found that the increase in risk for colorectal cancer was 16%, 21%, 15%, and 20% per unit increase in waist circumference, hip circumference, and waist-to-hip ratio respectively. The study concluded that greater BMI, waist circumference, hip circumference, and waist-to-hip ratio are associated with an increased risk of colorectal cancer in older adults.
Association with Gastroesophageal Cancer
A study published by the researchers from the First Affiliated Hospital of Soochow University in China evaluated the association between abdominal obesity, as measured by waist circumference and waist to hip ratio, with gastroesophageal cancer, gastric cancer and esophageal cancer. The analysis was done on 7 studies from 6 publications obtained through literature search in PubMed and Web of Science databases till August 2016. 2130 gastroesophageal cancer cases were diagnosed amongst 913182 participants during this period. The study found evidence of an increased risk of gastroesophageal cancer, gastric cancer and esophageal cancer with higher waist circumference and waist to hip ratio. (Xuan Du et al, Biosci Rep., 2017)
Association of BMI with Gastric Cancer
- Researchers from the Jilin University, Changchun in China evaluated the association between Body mass index (BMI) and risk of gastric cancer. 16 studies were used for the analysis which were obtained from the PubMed, Web of Science and Medline electronic databases. The results from the study indicated that obesity was associated with the risk of gastric cancer, especially in males and non-Asians. The researchers also found that both overweight and obesity were associated with the risk of gastric cardia cancer. (Xue-Jun Lin et al, Jpn J Clin Oncol., 2014)
- Another study published by the researchers of Seoul National University College of Medicine in Korea found that obesity was more prevalent in patients with gastric cardia adenocarcinoma compared to that in patients with gastric non-cardia adenocarcinoma. (Yuri Cho et al, Dig Dis Sci., 2012)
Association of Obesity with Thyroid Cancer
In a meta-analysis of 21 observational studies carried out by the researchers of Hubei Xinhua Hospital in Wuhan, China, they evaluated the association between obesity and thyroid cancer risk. The studies were obtained through literature search in PubMed, EMBASE, Springer Link, Ovid, Chinese Wanfang Data Knowledge Service Platform, Chinese National Knowledge Infrastructure (CNKI), and Chinese Biology Medicine (CBM) databases till 10th August 2014. Based on the findings from the study, the researchers concluded that obesity is associated with an increased thyroid cancer risk, except medullary thyroid cancer. (Jie Ma et al, Med Sci Monit., 2015)
Association of Obesity with Bladder Cancer Recurrence
Researchers from Nanjing Medical University, Jiangsu Vocational College of Medicine and Core Laboratory of Nantong Tumor Hospital in China carried out a meta-analysis of 11 studies obtained from literature search in Pubmed till Nov 2017, to explore whether obesity is related to overall survival and bladder cancer recurrence. The study found that for every unit increase in BMI, there was a 1.3% increased risk of bladder cancer recurrence. The study didn’t find any significant association between obesity and overall survival in bladder cancer. (Yadi Lin et al, Clin Chim Acta., 2018)
Association of Obesity and Overweight with Kidney Cancer Risk
Researchers from the Taishan Medical University and Traditional Chinese Medical Hospital of Taian in China carried out a meta-analysis to study the relationship between overweight/obesity and kidney cancer. The analysis used 24 studies with 8,953,478 participants which were obtained from PubMed, Embase, and Web of Science databases. The study found that compared to the normal weight, the increase in the risk of kidney cancer was 1.35 in overweight participants and 1.76 in obese participants. The study also found that for every unit increase of BMI, there was an increased kidney cancer risk of 1.06. (Xuezhen Liu et al, Medicine (Baltimore)., 2018)
Association of Obesity with Pancreatic Cancer Risk
In a study published in 2017, the researchers from France and the United Kingdom assessed the role of obesity, type 2 diabetes, and metabolic factors in pancreatic cancer. The study was conducted based on 7110 pancreatic cancer patients and 7264 control subjects using genome-wide data from the Pancreatic Cancer Cohort Consortium (PanScan) and the Pancreatic Cancer Case-Control Consortium (PanC4). The study found that an increase in BMI and genetically increased fasting insulin levels were associated with an increased risk of pancreatic cancer. (Robert Carreras-Torres et al, J Natl Cancer Inst., 2017)
Association of Obesity with Epithelial Ovarian Cancer Survival
Researchers Korea University College of Medicine did a meta-analysis to study the association between obesity and ovarian cancer survival. The analysis used 17 cohort studies from 929 screened articles obtained through literature search in databases including MEDLINE (PubMed), EMBASE, and Cochrane Central Register of Controlled Trials. The study found that obesity in early adulthood and obesity 5 years before the diagnosis of ovarian cancer were associated with poor patient survival. (Hyo Sook Bae et al, J Ovarian Res., 2014)
Association of Obesity with Lung Cancer Risk
Researchers from Soochow University in China carried out a meta-analysis to evaluate the association between obesity and lung cancer risk. 6 cohort studies obtained through literature search in PubMed and Web of Science databases up to October 2016, with 5827 lung cancer cases among 831,535 participants, were used for the analysis. The study found that for every 10 cm increase in waist circumference and 0.1 unit increase in waist-to-hip ratio, there was a 10% and 5% increased risk of lung cancer, respectively. (Khemayanto Hidayat et al, Nutrients., 2016)
Association of Obesity with Breast Cancer Risk
A nationwide cohort study based on data from 11,227,948 adult Korean women selected from the National Health Insurance Corporation database merged with national health examination data from 2009 to 2015, evaluated the association between obesity (as measured by BMI and/or waist circumference) and breast cancer risk. (Kyu Rae Lee et al, Int J Cancer., 2018)
The study found that increased BMI and waist circumference were associated with an increased risk for postmenopausal breast cancer, but not with premenopausal breast cancer. The study concluded that in premenopausal women, increased waist circumference may be used as a predictor for increased breast cancer risk only when BMI was considered.
In another study published in 2016, the researchers highlighted that the central obesity measured by waist circumference, but not by waist-to-hip ratio, may be associated with a modest increase in the risk of both premenopausal and postmenopausal breast cancer. (G-C Chen et al, Obes Rev., 2016)
Association of Obesity and Overweight with Cervical Cancer Risk
Researchers from Hamadan University of Medical Sciences and Islamic Azad University in Iran carried out a meta-analysis to evaluate the association between overweight and obesity and cervical cancer risk. 9 studies, obtained through literature search in PubMed, Web of Science, Scopus, ScienceDirect, LILACS, and SciELO databases up to February 2015, with 1,28,233 participants were used for the analysis. The study found that obesity may be weakly associated with an increased risk of cervical cancer. However, they didn’t find any association between cervical cancer and overweight. (Jalal Poorolajal and Ensiyeh Jenabi, Eur J Cancer Prev., 2016)
Association of BMI with Endometrial Cancer Risk
Researchers from Hamadan University of Medical Sciences and Islamic Azad University in Iran carried out a meta-analysis to evaluate the association between body mass index (BMI) and endometrial cancer. 40 studies involving 32,281,242 participants, obtained through literature search in PubMed, Web of Science, and Scopus databases until March 2015 as well as reference lists and related scientific conference databases, were used for the analysis. The study found that increased BMI may be strongly associated with an increased risk of endometrial cancer. (E Jenabi and J Poorolajal, Public Health., 2015)
Association of Obesity and Overweight with Gallbladder Cancer Risk
Researchers from Jiangxi Science and Technology Normal University and Huazhong University of Science and Technology in China carried out a meta-analysis to evaluate the association between overweight, obesity and the risk of gallbladder and extrahepatic bile duct cancers. 15 cohort studies and 15 case-control studies, involving 11,448,397 participants with 6,733 gallbladder cancer patients and 5,798 extrahepatic bile duct cancer patients, obtained through literature search in PubMed, Embase, Web of Science, and China National Knowledge Infrastructure databases up to August 2015, were used for the analysis. The average follow-up duration ranged from 5 to 23 years. The study found that excess body weight may be associated with a significantly increased risk of gallbladder and extrahepatic bile duct cancers. (Liqing Li et al, Obesity (Silver Spring)., 2016)
Different observational studies and meta-analyses provide strong evidence that obesity may be associated with an increased risk of a wide range of cancer types including liver, colorectal, gastro-esophageal, gastric, thyroid, bladder, kidney, pancreatic, ovarian, lung, breast, endometrial and gallbladder cancers. Many scientists also did extensive research to study how being overweight or obese may increase the risk of cancer.
Obesity is characterized by chronic low-grade inflammation and insulin resistance. The excessive fat cells present in obese people may result in changes in the environment within our body. The large collection of fat cells can lead to a low chronic inflammatory response in our body leading to the release of chemicals known as cytokines. Excess fat also makes the cells increasingly resistant to insulin, hence pancreas makes more insulin to compensate this ultimately resulting in very high levels of insulin in obese people. This can affect the levels of growth factors in our body. All these factors such as insulin, growth factors and cytokines can trigger the cells to divide rapidly in an uncontrolled manner resulting in cancer. Higher amounts of estrogen produced by fat tissue may also drive the development of cancers such as breast and endometrial cancers.
Maintaining a healthy weight by taking healthy food and doing regular exercises may help in reducing the risk of obesity/overweight-related cancers as well as recurrence of cancer in survivors. Use a BMI calculator to constantly monitor your body-mass index (BMI). Follow a diet that includes fruits, vegetables, whole grains and legumes/pulses such as beans and be healthy to stay away from a variety of obesity-related diseases including cancer.
“What should I eat?” is the most frequently asked question to cancer dieticians and physicians. The right answer depends upon cancer type, underlying genomics, current treatments, any allergies, lifestyle information, and factors like BMI.
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