The consequences are serious, as obesity is closely correlated with high blood pressure, diabetes, heart disease, and other serious health problems. Despite the magnitude of the problem, there is still no consensus on the cause, although scientists recognize many contributing factors, such as genetics, stress, viruses and changes in sleep habits. Of course, the popularity of highly processed foods (high in sugar, salt, and fat) has also played a role, especially in Western countries, where people on average consume more calories per day now than they did 50 years ago. Still, recent reviews of the science conclude that much of the huge rise in global obesity over the past four decades remains unexplained.
An emerging view among scientists is that one of the major overlooked components of obesity is almost certainly our environment, in particular, the pervasive presence of chemicals that, even in very low doses, act to alter the normal functioning of the human metabolism, altering the functioning of the body. ability to regulate your energy intake and expenditure.
Some of these chemicals, known as “obesogens,” directly stimulate the production of specific fatty tissue and cell types associated with obesity. Unfortunately, these chemicals are used in many of the most basic products of modern life, including plastic packaging, clothing and furniture, cosmetics, food additives, herbicides, and pesticides.
Ten years ago, the idea of chemically induced obesity was something of a fringe hypothesis, but not anymore.
“Obesogens are definitely a contributing factor to the obesity epidemic,” Bruce Blumberg, an obesity and endocrine-disrupting chemicals expert at the University of California, Irvine, told me by email. “The difficulty is determining what fraction of obesity is related to chemical exposure.”
Importantly, recent research shows that obesogens act to harm people in ways that traditional chemical toxicity tests cannot detect. In particular, the consequences of chemical exposure may not appear during the lifetime of an exposed organism, but may be transmitted through so-called epigenetic mechanisms to offspring, even several generations away. A typical example is tributyltin or TBT, a chemical used in wood preservatives, among other things. In experiments that exposed mice to supposedly safe, low levels of TBT, Blumberg and his colleagues found significantly more fat accumulation over the next three generations.
TBT and other obesogens trigger such effects by directly interfering with the normal biochemistry of the endocrine system, which regulates energy storage and use, as well as human eating behavior. This biochemistry depends on a wide variety of hormones produced in organs such as the gastrointestinal tract, pancreas, and liver, as well as chemicals in the brain capable of altering the sensation of hunger. Experiments have shown that mice exposed to obesogenic chemicals before birth exhibit significantly altered appetites later in life and a propensity for obesity.
Nearly 1,000 obesogens with such effects have already been identified in animal or human studies. They include bisphenol A, a chemical widely used in plastics, and phthalates, plasticizing agents used in paints, drugs, and cosmetics. Others include parabens that are used as preservatives in food and paper products, and chemicals called organotins that are used as fungicides. Other obesogens include pesticides and herbicides, including glyphosate, which a recent study found is present in the urine of most Americans.
Another clue that these chemicals may be behind obesity: Studies have found that the obesity crisis is also affecting cats, dogs and other animals that live near people. A significant increase in the incidence of obesity has even been observed in laboratory rodents and primates, animals raised under strictly controlled conditions of caloric intake and exercise. The researchers believe that the only possible factors driving these animals’ weight gain would be subtle chemical changes in the nature of the food they eat or the materials used to build their pens.
Therefore, we may have inadvertently saturated our living environment with chemicals that affect some of the most fundamental biochemical reactions that control human growth and development. The obesity epidemic is likely to persist or worsen unless we can find ways to remove such chemicals from the environment, or at least identify the most problematic substances and greatly reduce human exposure to them.
At a minimum, it will require a transformation in the way we test chemicals for toxicity, especially the many compounds that are ubiquitous in our foods, plastics, paints, cosmetics, and other products. Discoveries in epigenetics have profoundly changed medicine and basic biological science in the last 15 years, but have not yet had much impact on prevailing practices for chemical safety testing. Scientists are pushing for change, but it takes time.
Hopefully the appropriate testing methods will be adopted in the next few years. If they are not, we may have a hard time making an appreciable dent in this pernicious epidemic.
More from other writers at Bloomberg Opinion:
To fight hunger, we need to fix food subsidies: David Fickling:
Calorie counting is a boost, not a cure-all: Therese Raphael
Go ahead, order that cheesesteak: Faye Flam
This column does not necessarily reflect the opinion of the editorial board or of Bloomberg LP and its owners.
Mark Buchanan, a physicist and science writer, is the author of the book “Forecasting: What Physics, Meteorology, and the Natural Sciences Can Teach Us About Economics.”
More stories like this are available at bloomberg.com/opinion