The Environment and Obesity
KELLY D. BROWNELL
In this chapter, I take a strident stand, namely, that the epidemic of obesity seen in the United States, and increasingly so in other countries, is caused by the environment. Genetic and psychosocial factors may determine who in a given population is susceptible to a damaging environment (see Chapters 3, 4, and 5), but the number of people affected, and hence the public health burden, is dictated by the environment. In the absence of a “toxic” food and physical activity environment, there would be virtually no obesity.
This position differs from the default explanation that obesity is caused by a combination of genetic and environmental variables. This is true when one focuses on why an individual is obese, based on the medical model in which causes are sought for individual cases, and treatment rather than prevention is the aim (see Chapter 111 for a comparison of medical and public health models). Adopting a public health model to ask why a nation is obese leads squarely to the environment as the cause.
The past 20 years have seen an explosion of research on the biology of obesity and, in recent years, on genetics. This research is important, to be certain, in the hope that we learn more about individual susceptibility and develop better methods for treatment. Yet excitement about genetics threatens to obscure the obvious: that genetic susceptibly, no matter how strong, will rarely create obesity in the absence of a bad environment.
Searching for obesity genes in the hope of establishing cause may be akin to pursuit of a gene explaining lung cancer in smokers. True, the discovery might identify those most at risk and perhaps lead to ways to counteract the disastrous effects of tobacco, but the cause of the cancer is environmental. Removal of the toxin would eliminate most of the disease.
Individuals in the United States and in many other countries are exposed to an environment in which energy-dense foods are widely available, inexpensive, and promoted heavily, while at the same time energy-saving devices and other changes in lifestyle increase sedentary behavior (see Chapters 74 and 83). The only hope for changing the prevalence of obesity is to address these environmental causes (see Chapters 111 and 112).