You may have heard that being overweight or obese increases the odds of developing breast cancer. Studies do show a correlation between higher BMI with a stronger risk of developing breast cancer, but only in post-menopausal women. In pre-menopausal women, carrying extra body fat is somewhat protective and leaner women actually have a higher risk. Scientists believe that different risk factors and mechanisms may drive the development of premenopausal breast cancer.
Since breast cancer is more common after menopause, health care professionals point out the importance of maintaining a healthy BMI to lower breast cancer risk. Obesity is an established risk factor for post-menopausal breast cancer, according to the National Cancer Institute. But a new study shows that how much fat you carry around your waistline may be more important for determining the risk of breast cancer than BMI. Another reason to monitor the size of your waist!
This isn’t the first study to show belly and waist fat raise the risk of breast cancer more than fat stored in other areas of the body. Researchers at the University of Michigan did a study in 2017 that points to a possible reason why. They discovered that deep abdominal fat releases higher levels of a protein called fibroblast growth factor-2, or FGF 2. This protein encourages normal, healthy cells to turn into malignant cells. All fat cells release this growth factor, but visceral fat, a deep layer of abdominal fat, releases the most.
Studies link high levels of visceral fat with a number of health problems, including type 2 diabetes and cardiovascular disease. What is visceral fat? The fat stored around your abdomen has two different layers. The top layer is called subcutaneous fat. It’s the jiggly type of fat you can pinch between your fingers. But underneath that layer of loose fat lies a deep layer of visceral fat that builds up around organs, including the liver.
Along with fibroblast growth factor-2, visceral fat produces inflammatory chemicals called cytokines. These cytokines, by causing low-grade inflammation, may partially explain why visceral fat increases the risk of cardiovascular disease and other health problems. At least 13 cancers are linked with obesity and many obese people have higher levels of visceral fat. So, the cytokines released by visceral fat cells may play a role in causing cancer as well.
It’s unlikely that fibroblast growth factor-2 and cytokines are the only key players in breast cancer. Around 80% of breast cancers are estrogen receptor positive, meaning estrogen drives their growth. These tumors tend to have a better prognosis than estrogen receptor negative ones since you can use treatments that block the growth-enhancing effects of estrogen on the tumor. Obese and overweight women tend to have higher levels of estrogen naturally relative to lean women. Finally, insulin is a growth factor that may drive the proliferation of breast tumors. A number of cancer types are more common in people with insulin resistance, meaning they have higher levels of circulating insulin, and people with type 2 diabetes.
Even if you’re unfortunate enough to get breast cancer, body composition may play a role in your survival. Using CT imaging, a study published in the JAMA Oncology found that having high amounts of body fat and low muscle mass (sarcopenia) was associated with earlier death in breast cancer patients. Those with sarcopenia had a 41% higher mortality rate while breast cancer patients with both high amounts of body fat and sarcopenia had an 89% greater mortality rate.
So, avoiding excess fat, especially visceral fat, and maintaining muscle mass may be important for reducing breast cancer risk and for survival if you get it. Like many studies, the results only show an association, not necessarily causation. You can’t say excess fat around the belly causes breast cancer, although they’ve identified mechanisms that explain this association. That adds credibility to the results.
Tame That Belly Fat!
At the very least, we should try to reduce excess tummy fat for health purposes. As mentioned, visceral fat is linked to a variety of chronic health conditions. It’s also a marker of insulin resistance and poor metabolic health, and it gets tougher to fight visceral fat as we age. Hormonal changes, including a drop in estrogen and growth hormone and a rise in cortisol, makes it easier for your body to store excess energy viscerally. One marker of surplus visceral fat is a large waist size. For health reasons, your waist size should be no larger than half of your height. If you’re 5’4”, or 64 inches, your waist size should measure 32 inches or less. It’s just as important to watch your waistline and measure it regularly as it is to step on a scale. In fact, based on recent studies, it may be more important.
The causes of excess belly fat are multifactorial and linked to genetics and lifestyle habits. How can you fight it? Eat a whole food, nutrient-rich diet that includes lean protein, healthy fats, and lots of fruits and vegetables as opposed to overly processed foods and sugar. Make physical activity a standard part of your routine. Ideally, you need strength training and some form of aerobic exercise. That’s a good start, but don’t underestimate the importance that sleep and stress management play in controlling belly fat either. Lack of quality sleep and chronic stress raise cortisol, a stress hormone that shifts fat storage to the belly. It’s not always easy to control belly fat, but if you tackle these basics and are patient, you should see results over time.
The Bottom Line
How much fat you carry deep in your belly and around your waist may be more important risk factors than how much you weigh or your BMI. Know your numbers, including the size of your waistline and don’t let waist size slowly expand as you age.
· Cancer Therapy Advisor. “Waist Circumference Independently Associated with Breast Cancer Risk”
· ScienceDaily.com. “This is how belly fat could increase your cancer risk”
· American Institute for Cancer Research. “Low Muscle, High Body Fat Affects Breast Cancer Survivorship”
· JAMA Oncol. 2018;4(6):798-804. doi:10.1001/jamaoncol.2018.0137.
· National Cancer Institute. “Obesity”
· Int J Cancer. 2012 Feb 15; 130(4): 902–909.