To understand the relationship between obesity and cancer, at first, you have to know what obesity is. The condition, in which there is an unhealthy amount and/or distribution of body fat in a person’s body, is called obesity. A scale known as the body mass index (BMI) is commonly used by researchers to measure obesity. A person’s weight (in kilograms) is divided by their height (in meters) squared to calculate BMI. For most people, BMI is a fairly good (although indirect) indicator of body fatness. Sometimes, along with BMI, other measurements reflecting the distribution of body fat are increasingly being used as indicators of obesity and disease risks. Waist circumference and the waist-to-hip ratio (the waist circumference divided by the hip circumference) are included in these measurements.
Those who are overweight or obese are at greater risk for many diseases compared with people of normal weight. Diabetes, high blood pressure, cardiovascular disease, stroke and many cancers are some of these diseases. An increased death rate is also associated with extreme or severe obesity. Most of the excess deaths are caused by heart disease, cancer and diabetes.

The relationship between Obesity and Cancer

Large cohort studies, a type of observational study, is the source of nearly all of the evidence linking obesity to cancer risk. However, it cannot be definitively established by the data from observational studies that obesity causes cancer and these studies can be difficult to interpret. There are also other differences between obese or overweight people from lean people than differences in terms of the body fat. It is possible that the different cancer risk of obese or overweight people can be explained by these differences rather than the body fat. If you want to know a detailed description of this matter, a cancer specialist can tell you that.
However, there is consistent evidence despite the limitations of the study designs that increased risks of a number of cancers are associated with higher amounts of body fat. These cancers include:

  • Endometrial cancer : According to oncologists, The chance of development of endometrial cancer (cancer of the lining of the uterus) is two to about four times more likely in obese and overweight woman than normal-weight women and the chance of development of the more common of the two main types of this cancer is seven times more likely in extremely obese women. Particularly among women who have never used menopausal hormone therapy, with increasing weight gain in adulthood, the risk of endometrial cancer increases.

  • Esophageal adenocarcinoma : A type of esophageal cancer called esophageal adenocarcinoma is twice more likely to develop in overweight or obese people than in normal-weight people and the chance is four times more likely in extremely obese people.

  • Gastric cardia cancer : In the opinion of a cancer specialist, the chance of developing cancer in the upper part of the stomach i.e. the part closest to the esophagus is twice more likely in obese people than normal-weight people.

  • Liver cancer : Liver cancer is nearly twice more likely to develop in overweight or obese people in normal-weight people. In men, the association between overweight/obesity and cancer is stronger than in women.

  • Kidney cancer : According to oncologists, renal cell cancer, the common form of kidney cancer is twice more likely to develop in overweight or obese people than normal-weight people. The association of renal cell cancer with high blood pressure, a known risk factor for kidney cancer and the association of renal cancer with obesity are not dependent on each other.

  • Multiple myeloma : In the risk of developing multiple myeloma compared with normal-weight individuals, there is a slight (10% to 20%) increase in overweight and obese individuals.

  • Meningioma : There is a 50% increase in obese people and about a 20% increase in overweight people in the risk of this slow-growing brain tumour arising in the membranes surrounding the brain.

  • Pancreatic cancer : In the opinion of a cancer specialist, pancreatic cancer is 1.5 times more likely to develop in overweight or obese people than in normal-weight people.

  • Colorectal Cancer : The chance of developing colorectal cancer is about 30% more likely to develop in obese people than normal-weight people. In both men and women, increased risks of colon and rectal cancers are associated with a higher BMI, but in men, the increases are higher than in women.

  • Gallbladder Cancer : There is a slight (about 20%) increase in the risk of gallbladder cancer in overweight people compared with normal-weight people and the increase is 60% in obese people. In women, the risk increase is greater in men.

  • Breast Cancer : As a breast cancer doctor will tell you, a modest increase in the risk of breast cancer is associated with a higher BMI in postmenopausal women according to many studies. The risk of developing breast cancer among postmenopausal women is 20% to 40% more in those who are obese than those who are normal weight. In women who have never used menopausal hormone therapy, the higher risks are mainly seen and they are also for tumours expressing hormone receptors. In men, obesity is also a risk factor for breast cancer. A 20% decreased risk of breast tumours that express hormone receptors have been associated with overweight and obesity in premenopausal women.

  • Ovarian Cancer : Particularly in women who have never used menopausal hormone therapy, higher BMI is associated with a slight increase in the risk of ovarian cancer.

  •  Thyroid cancer : With a slight increase in the risk of thyroid cancer, higher BMI is associated.