Shocking but true: according a poll published this week, only 7% of Americans understand that being obese increases a person’s cancer risk.
Disappointingly, this comes after years of tireless awareness-raising campaigns by organizations like the American Institute for Cancer Research (AICR) and the American Cancer Society (ACS), who have been issuing increasingly stern warnings about the link between obesity and cancer. For being overweight and obese not only boosts everybody’s risk of developing cancer, it also reduces cancer patients’ chances of survival after a successful cancer treatment.
So serious are the cancer implications of carrying excess weight that some are now dubbing obesity “the new smoking” . The ACS estimates that about one third of the 500,000 American cancer deaths a year are related to physical activity and diet and another third are tobacco related. If current trends for smoking and obesity continue, obesity will soon overtake tobacco use as the number one preventable cause of cancer, the organization has predicted.
According to the 2007-2008 National Health and Nutrition Examination Survey, 68% of Americans age 20 years and older are overweight or obese. In 1988-94, by contrast, only 56% of adults were overweight or obese. Over the same period, the percentage of overweight or obese children increased to 17% from 10%.
Meanwhile, the World Cancer Research Fund estimates that in the U.S., a whopping 49% of endometrial cancers, 32% of esophageal cancers, 20% of kidney cancers, 17% of breast, colo-rectal and pancreatic cancers and 11% of gallbladder cancers could be prevented if people had a healthy body weight (i.e. a body-mass index in the normal range).
Current guidelines from the U.S. Centers for Disease Control and Prevention and the World Health Organization define a normal BMI range as 18.5 to 24.9. Overweight is defined as a BMI of 25.0 to 29.9; obesity is defined as a BMI over 30.0; and severe obesity is defined as BMI 35 or higher. For a BMI calculator, go to http://www.nhlbisupport.com/bmi/bmicalc.htm.
How does obesity raise our cancer risk?
According to the National Cancer Institute, several mechanisms may explain the association of obesity with increased risk of certain cancers:
- Fat tissue produces excess amounts of estrogen, high levels of which have been associated with the risk of breast, endometrial, and some other cancers.
- Obese people often have increased levels of insulin and insulin-like growth factor-1 (IGF-1) in their blood (a condition known as hyperinsulinemia or insulin resistance), which may promote the development of certain tumors. (Read more about insulin and IGF-1 on our blog “Anti-Cancer Nutrition: Sugar and Carbohydrates 101.”)
- Fat cells produce hormones, called adipokines, that may stimulate or inhibit cell growth. For example, leptin, which is more abundant in obese people, seems to promote cell proliferation, whereas adiponectin, which is less abundant in obese people, may have antiproliferative effects.
- Fat cells may also have direct and indirect effects on other tumor growth regulators, including mammalian target of rapamycin (mTOR) and AMP-activated protein kinase. (Read more about how a plant-derived diabetes medication inhibits mTOR and AMP-kinase on our blog)
- Obese people often have chronic low-level, or “subacute,” inflammation, which has been associated with increased cancer risk. (Read more about this on our blog post “Inflammation 101: The Fuel That Feeds Cancer“.)
Other possible mechanisms include impaired immune responses and increased oxidative stress associated with excess weight, according to the NCI.
Not only is there strong evidence that if you’re overweight, you’re more likely to die of cancer. It’s also been shown that the more overweight you are, the more deadly the trend gets, according to a study published in the New England Journal of Medicine in 2003.
Here, ACS scientists looked at cancer death rates for men and women in five weight categories: healthy (body mass index of 18.5 to 24.9); overweight (BMI, 25 to 29.9); and three levels beyond: “obese” (BMI, 30 to 34.9), “very obese” (BMI, 35 to 39.9) and “very, very obese” (BMI, 40 or more). Compared with death rates for men and women of healthy weight, death rates from all cancers lumped together as a group rose consistently along with BMI: Rates were 52% higher for very, very obese men and 62% higher for very, very obese women.
So imagine my frustration when the media last week breathlessly proclaimed that being pudgy might actually be healthier than having a healthy weight! They based this assertion on a study published in the Journal of the American Medical Association which found that people who were modestly overweight – in the 25-30 BMI range – had a slightly lower risk of premature death than normal-weight individuals.
The AICR was quick to quell optimism by pointing out that this study only showed a general association between premature death and BMI, but did not examine what causes people had died of.
“For cancer risk the evidence is clear,” AICR Director of Research Susan Higginbotham, PhD, MPH, RD commented in a blog post. “Our expert report and its updates show that body fatness increases the risk of several common kinds of cancer.”
So where does this leave overweight and obese individuals wishing to lower their risk of developing cancer? At the risk of sounding like a broken record, shifting to a traditional Mediterranean Diet would be a great start.
This way of eating – characterized by high intakes of vegetables and fruits, healthy fats, nuts and seeds, legumes and whole grains, oily fish and lean meat and an absence of processed food – has been shown over and over again to help achieve and maintain healthy weight (here’s just a short list of studies supporting this ) and to reduce cancer risk (as I describe in Zest for Life, The Mediterranean Anti-Cancer Diet).
Add to this regular physical activity, stress management and adequate sleep (all of which are part and parcel of the Mediterranean lifestyle, as described in this inspiring article), and you are looking at significantly lowering your risk of cancer as well as many other health problems such as diabetes, cardiovascular disease, obesity, infertility, depression and dementia.
It’s not too late to add a New Year’s Resolution to your list: Go Mediterranean!