How much of a problem is obesity?
Suppose there was a condition affecting 30-40 percent of the U.S. population that increased the risks of developing and dying of heart disease, diabetes and colon and breast cancers. What if this condition affected 15-20 percent of children? What if this condition were treatable by low-cost interventions that individuals could do on their own? That’s obesity, and it is rightly labeled an epidemic. The Centers for Disease Control and Prevention estimates more than 78 million adults and 12.5 million children were obese in the years 2010-12. Obesity and being overweight contributes to about 1 in 10 U.S. deaths, and the overall costs of this problem are $220 billion per year.
What exactly is meant by obesity?
Body mass index (BMI), which is the function of your height and weight, categorizes individuals into four BMI groups: underweight, less than 18.5; normal weight, 18.5-24.9; overweight, 25-29.9 and obesity, 30 or greater. There are several free online BMI calculators (found at websites nhlbi.nih.gov/guidelines/obesity/BMI/bmicalc or webmd.com/diet/calc-bmi-plus). For example, if your height is 5 feet, 4 inches and your weight is 174 pounds, or a height of 5 feet, 9 inches and weight of 203 pounds, your BMI is 30.
Many factors contribute to this epidemic of obesity, but the two main factors are over the past 50 years collectively we have spent increased amounts of time both in and outside of work being less physically active. In parallel, over that time, the daily calories we have consumed have increased. It really all boils down to a simple equation: Less physical activity + more calories consumed = weight gain.
How does obesity affect the risks of developing breast cancer?
Multiple studies show obesity increases the risk of developing breast cancer. Likewise, once a woman is diagnosed with breast cancer, obesity increases the risks of having a recurrence and of death. There are several explanations of why this is. In postmenopausal women, estrogen is produced by adrenal glands and fat cells, particularly the fat cells that surround the mid abdomen, which is called centripetal obesity. More fat cells increase production of estrogens and higher estrogen levels are associated with increased risks of developing breast cancer — or more likely causing microscopic, undetectable breast cancers to grow sufficiently so that they become detectable.
Obesity in general and centripetal obesity in particular are also associated with higher insulin levels, insulin resistance (when the body requires more and more insulin to regulate glucose or sugar) and the metabolic syndrome (characterized by high blood sugars, high blood lipids, centripetal obesity and high blood pressure). Insulin and related proteins are growth factors for breast cancer cells, so this represents another possible mechanism of obesity increasing the risks of breast cancer.
Finally, in most studies obesity increases the risks of breast cancer only in postmenopausal women. These results were called into question by a more recent study showing higher risks of breast cancer in premenopausal women, but not postmenopausal women. These contrasting results are common in the medical literature, and single studies usually don’t provide enough evidence to draw any conclusions. However, obesity in girls and women, irrespective of age or menopausal status, is to be avoided.