By Irene Fried
Most American adults are burdened with excess weight, a nationwide condition that is worsening quickly and dramatically. Current estimates are that 117 million adults weigh too much; of these, 57 million are obese as measured by a body mass index (BMI) of 25 or more. In a recent presentation, Larry Fields, M.D., assistant secretary for health, Office of Public Health Science, Department of Health and Human Services, stated that projections based on the increases we’ve seen over the last several years would put the current figure of overweight Americans at 75 or 80 percent. Most of this epidemic increase comes from obesity rather than overweight. Every area of the country is affected, as are both sexes, smokers, non-smokers, and people of all ages, every ethnicity, and each level of educational attainment.
Simply stated, it is a basic energy imbalance that leads to excess weight – consuming more calories than we expend in a day causes weight gain. Over time in the U.S., we have increased average total energy intake by 300 calories a day while becoming increasingly sedentary – and carrying more fat.
The Rand Institute concluded in 2002 that obesity is linked to greater health risk and higher health expenditures than smoking, heavy drinking or living in poverty.
Our best data, says Fields, indicate that three to seven years are shaved off life expectancy from overweight and obesity, and the argument has been advanced that being obese is like aging twenty years. The health costs of obesity arise every day in the excess burden of disease (including cardiovascular disease and diabetes), impairment of physical strength, and premature death.
We are also learning more about the contribution of obesity to morbidity and mortality from cancer. Studies have demonstrated that obesity increases the risk of cancers of the breast, colon, prostate, endometrium, cervix, ovary, kidney, and gallbladder. Researchers have also found an increased risk for cancers of the liver, pancreas, rectum, and esophagus. Because obesity is so prevalent in the U.S., small increases in risk translate into substantial numbers of cancers that are related to overweight or obesity.
Obese individuals fare worse on average with cancer diagnoses than do their leaner cohorts, and there is new information addressing not just cancer incidence but risk of death from the disease. Results of the most comprehensive U.S. study to date on cancer mortality from obesity were published in the April 24, 2003 issue of The New England Journal of Medicine. Calle et al. conclude from a prospective study of 900,000 men and women that “current patterns of overweight and obesity in the United States could account for 14 percent of all deaths from cancer in men and 20 percent of those in women.” In other words, one in five women dying of cancer could potentially attribute the cause of that cancer to her weight. If in fact this relationship between obesity and cancer is a causal one, the authors suggest that the U.S. could avoid more than 90,000 deaths per year from cancer if every adult maintained a BMI under 25.0 throughout life.
BMI was found to be associated with higher death rates in both women and men from cancer of the esophagus, colon and rectum, liver, gallbladder, pancreas, and kidney, as well as non-Hodgkin’s lymphoma and multiple myeloma. In men, higher BMI was linked to increased risk for death from stomach and prostate cancer, and in women from breast, uterine, cervical and ovarian cancer.
The heaviest subjects in the study, those with a BMI of at least 40, had death rates that were 52 percent higher for men and 62 percent higher for women than those with BMI under 25. Among women with BMI of 40 or more who had never smoked, the risk of death from any cancer was increased by 88 percent. Non-smokers, say the authors, provide better indication of the magnitude of increased risk from obesity, as smoking itself decreases body mass and increases risk of cancer death.
The increased cancer risk is greater overall for women than for men. “Increases in risk associated with obesity are more striking in women than in men because relatively more of the cancers that are common in women, such as breast and endometrial cancer, are associated with obesity,” explains Rachel Ballard-Barbash, M.D., MPH, associate director, applied sciences at the National Cancer Institute (NCI). “We’ve known for many years that a high BMI markedly increases risk for endometrial cancer, and now there is very consistent evidence that it also increases risk for post-menopausal breast cancer as well as other types of cancers.”
The biological mechanisms that link obesity to most cancers have been difficult to pinpoint. The International Agency for Research on Cancer (IARC), a part of the World Health Organization (WHO), has deemed the state of evidence sufficient to say that avoiding weight gain has a cancer-preventive effect for cancers of the colon, breast (in postmenopausal women), endometrium, kidney (renal-cell carcinoma), and esophagus (adenocarcinoma). The exact means by which excess weight might lead to cancer, however, are not fully known. Increased levels of hormones, including sex steroids, insulin, and insulin-like growth factor (IGF) have been noted as potential biologic mechanisms in cancer development.
Breast cancer was among the first cancers in which a link to diet and excess weight was postulated. “The leading hypothesis regarding increased risk for breast cancer in post-menopausal women is related to increases in estrogen, particularly estradiol, in heavy compared to lean post-menopausal women,” says Ballard-Barbash. “Among women who do not use hormone therapy, the major source of estradiol in postmenopausal women is the production of estrogen from fat tissue.”
Excess weight is also associated with worse outcomes for those with a breast cancer diagnosis. According to Ballard-Barbash, “There are many studies that have looked at breast cancer mortality and breast cancer prognosis or recurrence. We know that irrespective of menopausal status at diagnosis, women who are heavy and those who gain weight after diagnosis and during treatment are much more likely to do poorly following their breast cancer diagnosis. They are more likely to have their disease recur and have shorter survival. Not all of that decrease in survival is due to death from breast cancer – some of it may be due to death from co-morbid conditions, such as diabetes or cardiovascular disease.”
In the prospective study by Calle, et al., most cancers, covering a wide spectrum of sites, showed positive associations between excess body weight and increased mortality, indicating that much research is yet to be done to offer explanation. “The NCI is continuing to be very active in advancing research to understand the role of obesity, sedentary lifestyle and diet as it relates to cancer incidence, morbidity, quality of life and mortality,” said
Ballard-Barbash. “Efforts are expanding to characterize the mechanisms by which this happens, because it is through better understanding of those mechanisms that we obtain clues on how we can more effectively intervene. Investigators are examining the effect of sex steroids, insulin and IGF related factors, as well as alterations in immune function and inflammatory factors. The next few years should also lead to substantial progress in understanding if there are differential responses by genetic or other approaches to characterizing individual level risk.”
Whatever the magnitude of effect genetics will prove over time to have as a challenge to weight homeostasis, the preponderance of data show that our underlying genetics protect against weight loss more than prevent weight gain, making exercise an inextricable component of weight control. Our westernized lifestyle, however, has become increasingly sedentary.
Says Ballard-Barbash, “Sedentary lifestyle and obesity cause increased exposure to sex steroids in women, which may be increasing their breast cancer and endometrial cancer risks. One approach is to use a chemopreventive agent, such as tamoxifen, that has been demonstrated to be effective in breast cancer prevention. However, many women are interested in other non-pharmacologic approaches to improving overall health, in part due to some of the recent questions that have been raised about the effect of hormone replacement therapy. The evolving evidence on the importance of obesity and physical activity to cancer risk and prognosis argues for an increased focus on the prevention of obesity and avoidance of sedentary lifestyles. We need to provide services not just for treating obesity, but for actually preventing obesity. That would require that physicians monitor weight and engage people actively in efforts to control weight. This does not happen currently, even for patients with a disease, such as hypertension, that might resolve completely with treatment. A physician is much more likely to prescribe a drug as opposed to advising a very active six-month course of diet and physical activity to control weight. To me, that’s a major failure of our medical system, and could be corrected. The question of insurance coverage for preventive services remains a crucial issue. Presently, treatment of obesity is covered as part of treatment for associated co-morbidities, such as hypertension, diabetes or heart disease. But if the goal is to prevent those diseases then weight control should start much earlier, even before these conditions develop. There has been a longstanding tradition of using dieticians and nurse educators in treatment of diabetics. Weight control as part of that treatment is well accepted. Given the rising epidemic of obesity in the U.S., efforts to control it will require concerted efforts in clinical practice, including improved insurance coverage, and effective clinical practice routines that include physicians and associated health care providers in prevention, as well as management of obesity. In addition, comprehensive public health campaigns and efforts to address the many environmental and structural factors that could combat obesity are needed. ”
A simple but key involvement for physicians that has been suggested by obesity prevention advocates is to make a discussion of weight and BMI a routine part of a regular physical exam. In a non-judgmental way, a physician would discuss pulse, weight and BMI along with other routine measurements.
Prevention measures of all types – controlling calories, increasing physical activity, having appropriate health screenings, etc. – are clearly the key to making any headway against the sweeping tide of obesity with its range of dire consequences. It is widely noted that because of obesity, we may be seeing the first generation whose life expectancy will decrease rather than increase.
James Hill, Ph.D., a researcher at the University of Colorado has pointed out that “becoming obese is a normal response to the American environment.” It is an environment of automobiles, super-sized fast food, and leisure hours spent in front of a screen. It is empirically undeniable that the choices we have made over the past half-century have led to the transition to obesity. If we do not adapt to our environment by making better choices, not even our best medicine is ready to reverse the morbid consequences to our health.
Irene Fried is a freelance writer based in Raleigh, N.C.
