On this blog and in Healing, Meaning and Purpose, I have talked about some of the less well recognized contributors to obesity, including:
There is some new evidence from Korea published in the journal Diabetes Care, supporting the possible contribution of pesticides to insulin resistance.
People with high levels of persistent organic pollutants (POPs) in their blood were more likely to develop insulin resistance, which may lead to type 2 diabetes. Insulin resistance may also lead to obesity, hypertension and an array of other diseases. It is well recognized that increasing amounts of intra-abdominal fat may increase insulin resistance. It is less well known that this obesity is part of a viscous circle, with insulin resistance being associated with elevated insulin levels that may cause fat to be laid down throughout the body. Once the fat is laid down in the abdomen, it can break down, releasing fatty acids and triglycerides that in turn affect the breakdown of insulin by the liver and the release of insulin by the pancreas.
Previous research by the same group found a link between POPs and type 2 diabetes. This study confirms that background exposure to some POPs, chemicals such as organochlorine pesticides and polychlorinated biphenyls (PCBs), is also associated with insulin resistance among people who do not yet have diabetes.
The researchers also found that the association between organochlorine pesticides and insulin resistance became stronger as people got fatter. However, among people who had very low concentrations of pesticides in their blood, the researchers found little association between waist size and insulin resistance.
Some studies have suggested an association between background exposure to POPs and a variety of adverse health effects in humans and wildlife. POPs can be particularly problematic because they persist for long periods of time in the environment, accumulate up the food chain, and can travel great distances through the air and water. Therefore, even people and animals that live nowhere near a place where POPs are being applied often show high levels of these chemicals in their bloodstream.
An international treaty banning a dozen of the world's most dangerous POPs has helped reduce exposures, but many harmful chemicals remain in use and even those that have been banned may linger in our environment for years to come. For example, chlordane was banned two decades ago in the United States but continues to be present at high levels in our food supply.
The researchers concluded that some POPs "may be involved in the pathogenesis of insulin resistance." They advise urgent prospective studies among those who have background exposure to POPs, which mostly comes from eating fatty animal foods. Since obesity may increase the toxicity of POPs, controlling weight could also help to reduce the impacts of these molecules.
In separate research involving mice, Frederick vom Saal from the University of Missouri in Columbia, Missouri has studied the effects of a different class of endocrine-disrupting chemicals, including bisphenol-A (BPA). Not long ago, BPA made news in San Francisco, where there was a lot of controversy over an ordinance that seeks to ban its use in children's products. vom Saal's most recent work was presented at the 2007 Annual Meeting of the American Association for the Advancement of Science (AAAS). He found that endocrine-disrupting chemicals cause mice to be born at very low birth weights and then very rapidly gain abnormally large amounts of weight: they could more than double their body weight in just seven days. Vom Saal followed the mice as they got older and found that these mice were obese throughout their lives. He said studies of low-birth-weight children have shown a similar overcompensation after birth resulting in lifelong obesity.
(Regular readers might remember the concept of the thrifty phenotype, and see how this research ties in with that concept). More research must be done to determine which chemicals cause this metabolic effect. According to vom Saal, there are approximately 55,000 manmade chemicals in the world, and 1,000 of those might fall into the category of endocrine disrupting. These chemicals are found in common products, from plastic bottles and containers to pesticides and electronics.
These chemicals are so pervasive that it is difficult to avoid them, and there is scant evidence that "detoxification" helps clear them. That being said, and depsite the lack of evidence, we recommend certified organic produce and regular mild detoxification programs, together with nutritional support and tapping therapies.