Whether you blame your expanding waistline on too much pizza, lack of exercise or simply aging, shrugging off those pounds can have dire consequences.
You probably knew that weighing too much boosts your cardiovascular risk. But you may not know that excess weight also increases your chance of developing 13 types of cancer, including those of the bowel, breast, endometrium (uterine lining), esophagus, gallbladder, kidney, ovary and pancreas. The American Cancer Society states that overall, excess body weight is believed to be responsible for about 8% of all cancers.
In fact, next to smoking, being overweight is the single biggest preventable cause of cancer, according to a 2017 study in the British Journal of Cancer. In this study, which involved more than 43,000 participants tracked for longer than 12 years, researchers found that adding about 4 inches to your waistline increases the risk of obesity-related malignancies by 13%. Adding 3 inches to the hips was found to boost bowel cancer risk by 15%.
Although no particular level of obesity or excess body fat appears to be a tipping point into a danger zone, “for most cancers, there appears to be a linear relationship,” says Kathleen M. Egan, PhD, of the Moffitt Cancer Center in Tampa. “The greater the level of obesity, the higher the risk.”
And it’s not just the weight itself but where you gain excess fat that influences the type of cancer you’re more apt to develop.
Abdominal obesity, for example, is most often linked to the risk of cells becoming cancerous. Belly fat consists of two layers: the one directly under the skin known as subcutaneous fat, and visceral fat, which lies below this top layer. This deeper visceral fat is seen as most harmful in general, and it directly links to the spread and growth of ovarian cancer as well as colon cancer.
In certain cancers, such as that of the endometrium, obesity is considered an especially strong risk factor, says Egan. “In breast cancer, on the other hand, the relationship is more complex. A high level of body fat in adulthood links to increased risk of breast cancer after menopause [when the majority of breast cancers are diagnosed] but a lower risk of premenopausal breast cancer,” Egan adds. “Weight gain in adulthood increases risk over and above a higher level of body fatness.”
The association of body fat and cancer becomes easier to understand when you look at the many roles adipose (fat) tissue plays.
While known predominantly as a form of energy storage, adipose tissue plays a lesser-known role as an active endocrine organ that produces hormones, growth factors and signaling molecules, says Egan. “These substances can act locally in tissues in the area of the fat and systemically throughout the body by circulation in the blood. Obesity, particularly visceral fat, leads to physiological changes and a range of effects that contribute to cancer,” she explains.
Obesity-related inflammation is also believed to play a role. “For one thing, we think obesity itself is a chronic inflammatory condition,” says Timothy E. Byun, MD, an oncologist with St. Joseph’s Hospital in Orange, California. “This suggests that obese people have chronic inflammation, a contributing factor for cancer formation.”
“Chronic inflammation is the most common association linking cancer and body fat,” adds Adil Akhtar, MD, an oncologist and associate professor at Oakland University William Beaumont School of Medicine. “An example is chronic acid reflux from the stomach to the esophagus in overweight people, which leads to inflammation and ultimately cancer of the esophagus.”
Over time low-level inflammation results in the development of unstable compounds called free radicals. “They are produced from inflammatory cells and cause DNA damage.” says Egan. For instance, she explains that various adipokines (fat cells that participate in cell signaling, or communication between cells) “contribute to local and systemic inflammation.”
Hormonal changes can also increase cancer risk. Fat tissue produces excess amounts of the hormone estrogen, explains Akhtar, who says, “This has been associated with increased risks of breast, endometrial, ovarian and some other cancers.”
Byun notes that some theorists “associate increased leptin levels with cancer risk.” Leptin is a hormone that regulates appetite, energy expenditure and body composition (more lean muscle than fat, or vice versa). A dysfunction in leptin regulation is believed to play a role in the development of several cancers, including those of the breast, endometrium, gastrointestinal system and thyroid. “We don’t completely understand how these cancers link to body fat,” adds Akhtar. “But there is clearly an overall increased risk of cancer.”
Aging Adds Risk
Age presents another risk factor for cancer—one that is, unfortunately, not modifiable. “We’re more likely to develop cancer as we age, especially with colon cancer and certain blood cancers such as lymphoma,” says Byun.
Aging is believed to affect cancer risk in two ways. “One theory is that as you age, your body’s immune system isn’t as robust and is unable to take out these cancer cells early on,” says Byun. In addition, the physiological “machinery” that allows copying of DNA of cells may go awry. “This process has to be perfect,” Byun notes. “It’s a very tightly regulated system. So this mechanism has to make a perfect copy of that cell. As one gets older there’s a decline in the ‘checks and balances,’ and this results in more DNA mutations.”
Interestingly, the age at which a person gains excess weight may also impact cancer risk. “Obesity at a young age may reduce breast cancer before menopause, but obesity after menopause and weight gain in adulthood is linked to increased breast cancer,” says Egan. In other types of cancer the opposite holds true. For example, women who are overweight as teenagers may be at a higher risk for developing ovarian cancer before menopause, according to the American Cancer Society.
Sarcopenia, the loss of muscle mass associated with aging, combined with obesity later in life, is considered a particularly high-risk combination. “A major subset of adults over the age of 65 is now classified as having ‘sarcopenic obesity,’” says Egan. “This underscores the importance of calorie restriction, protein supplementation and aerobic and resistance exercises as we age.”
Reduce Weight, Reduce Risk?
If excess body fat is associated with increased cancer risk, it makes sense that weight loss should reduce this risk.
Much evidence shows this to be true, says Egan. “Bariatric surgery is associated with a significant reduction in overall cancer,” she explains. “The procedure reduces risk of endometrial cancer by up to 81% in obese women who attain and maintain a normal weight. Studies have also shown that weight loss reduces specific cancers including that of breast.”
Changes in estrogen metabolism and breakdown may be one of the ways in which aerobic exercises lowers a woman’s breast cancer risk, according to a study from the American Association for Cancer Research. Participants in this study exercised five days a week for a minimum of 45 minutes, the current national recommendation. Weight loss was modest, but the exercisers lost between 3% and nearly 7% of their visceral fat while maintaining the same calorie intake.
Weight loss in general also reduces biomarkers associated with cancer, and it seems more effective than exercise alone without weight loss. However, exercise on its own reduces cancer risk as well. “Living a sedentary lifestyle, eating an unhealthy diet and excessive alcohol intake also account for the burden of cancer by promoting obesity,” says Egan. Unhealthy lifestyle habits such as a lack of physical activity along with high consumption of red and processed meats, and of ultra-processed foods, all increase cancer risk.
Getting regular, moderate-intensity exercise is particularly important to reduce cancer risk in postmenopausal women, according to a study from the Fred Hutchinson Cancer Research Center in Seattle. The scientists noted that even if women do not see a change when they step on the scale, regular exercise reduces visceral fat.
“Smoking prevalence is dropping at the same time that obesity prevalence has increased,” notes Egan. “This means obesity may be as important as smoking as a contributor to overall mortality and cancer, and may even surpass it.
Colorful Cancer Prevention
If you’ve ever admired the bright yellows and reds in the produce aisle, you should know they’re more than just eye-catching: The bold colors in fruits and vegetables indicate the presence of phytonutrients, substances that boost well-being in a number of ways, including cancer prevention. Produce also supports health by providing fiber along with vitamins and minerals.
Here are some of the cancer-fighting phytonutrients found in fruits and vegetables from all along the color spectrum.
White-yellow: allicin, found in garlic, leeks, onions, scallions and shallots; limonoids, found in grapefruits, lemons, limes, noni and oranges; carotenoids, found in apricots, bell peppers, carrots, collard greens, kale, lettuce, mangoes, papayas, spinach, sweet potatoes and winter squash
Green: catechins, found in apples, berries and green tea; chlorophyll, found in all green plants, with barley and wheat grasses, the algae chlorella and spirulina, and leafy greens as especially rich sources; sulforaphane, found in broccoli (especially broccoli sprouts), brussels sprouts and cabbage
Red-purple: lycopene, found in grapefruits, tomatoes and watermelons; ellagic acid, found in grapes, pomegranates, raspberries and strawberries; resveratrol, found in grapes and peanuts; anthocyanins, found in açai, bilberries, blackberries, black currants, blueberries, cherries, cranberries, goji, grapes, mangosteen and plums