Chemicals and obesity
What is obesity?
Obesity is the excess accumulation of body fat, to the degree that it becomes harmful to health. 26 percent of men and women in the UK are obese. In the US, 32 per cent of men and 35 per cent of women are obese. By 2030, it is expected that 50 per cent of US and 40 per cent of UK adults will be obese. By this point obesity will have overtaken smoking as the biggest preventable cause of chronic, non-communicable diseases (Wang et al. 2011).
What are obesogens?
Obesogens are chemicals which affect the body’s ability to control its weight. We know that diabetes drugs cause obesity, and researchers have also discovered that the children of mothers who smoke while pregnant are much more likely to become obese (Monasta et al. 2010).
We do not really understand how chemicals can cause obesity. However, experiments have shown that the antifouling agent tributyl tin causes rats to produce more fat cells than usual (Kirchner et al. 2010). Other experiments have found that the oestrogenic drug diethylstilboestrol (DES) makes a mouse’s metabolism act as if it is in a low-food environment, so the mouse becomes fat if food is in fact plentiful (Newbold et al. 2009).
Which chemicals are obesogens?
Very few chemicals have been tested to find out if they are obesogens. Studies have found that the offspring of pregnant rats exposed to small quantities of bisphenol A (BPA) gain more weight than is normal, especially when on a diet high in fat (Wei et al. 2011). Similar effects have been found for organophosphate insecticides (Slotkin 2011).
Epidemiological studies have found that people exposed to persistent organic pollutants (POPs) tend to have more body fat than normal (Lee et al 2011). Other chemicals which may be obesogenic include non-stick PFOAs, phthalates, nonylphenol, dioxins and furans, small particulates in air pollution and some brominated flame retardants.
Minireview: the case for obesogens. Two leading US obesogen researchers present a short summary of the evidence for chemical causes of obesity.
Environmental estrogens and obesity. The researcher who discovered that low doses of DES could make mice fat by changing how much energy they store from food reviews the connections between xenooestrogens and obesity.
Obesogens. High-quality Wikipedia article giving a brief overview of the basic theory of obesogenicity.
The Obesogen Hypothesis. An article explaining how relatively minor alterations to energy balance can result in substantial weight gain, and the evidence that chemicals we encounter in the environment may be able to cause this.
Selection of references
Kirchner S, Kieu T, Chow C, Casey S, Blumberg B. Prenatal exposure to the environmental obesogen tributyltin predisposes multipotent stem cells to become adipocytes. Mol Endocrinol. 2010 Mar;24(3):526-39. Epub 2010 Feb 16. PubMed PMID: 20160124; PubMed Central PMCID: PMC2840805.
Lee DH, Lind L, Jacobs DR Jr, Salihovic S, van Bavel B, Lind PM. Associations of persistent organic pollutants with abdominal obesity in the elderly: The Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study. Environ Int. 2011 Aug 9. [Epub ahead of print] PubMed PMID: 21835469
Monasta L, Batty GD, Cattaneo A, Lutje V, Ronfani L, Van Lenthe FJ, Brug J. Early-life determinants of overweight and obesity: a review of systematic reviews. Obes Rev. 2010 Oct;11(10):695-708. doi: 10.1111/j.1467-789X.2010.00735.x. Review. PubMed PMID: 20331509.
Newbold RR, Padilla-Banks E, Jefferson WN. Environmental estrogens and obesity. Mol Cell Endocrinol. 2009 May 25;304(1-2):84-9. Epub 2009 Mar 9. Review. PubMed PMID: 19433252; PubMed Central PMCID: PMC2682588.
Slotkin TA. Does early-life exposure to organophosphate insecticides lead to prediabetes and obesity? Reprod Toxicol. 2011 Apr;31(3):297-301. Epub 2010 Sep 17. Review. PubMed PMID: 20850519; PubMed Central PMCID: PMC3025269.
Wang YC, McPherson K, Marsh T, Gortmaker SL, Brown M. Health and economic burden of the projected obesity trends in the USA and the UK. Lancet. 2011 Aug 27;378(9793):815-25. PubMed PMID: 21872750.
Wei, J, Y Lin, Y Li, C Ying, J Chen, L Song, Z Zhou, Z Lv, W Xia, X Chen, and S Xu. 2011. Perinatal exposure to Bisphenol A at reference dose predisposes offspring to metabolic syndrome in adult rats on a high-fat diet. Endocrinology http://dx.doi.org/doi:10.1210/en.2011-0045.