A growing number of people are unable to shed those extra pounds despite strict diet regimes and long hours of workout. Evidence shows that the toxins in the environment could be playing the spoilsport. They modify the body’s physiology and make it difficult to lose weight. While the West is waking up to the complex linkages between chemicals and obesity, realization is yet to dawn on doctors and researchers in India. Vibha Varshney, Dinsa Sachan and Sonal Matharu report on the new trigger for obesity and the way out.
Obesity has just slipped out of the grasp of mathematical logic: if one burns as many calories as one consumes, one will not gain weight. Today it is easy to spot people in jogging parks, aerobic centres and gymnasiums who defy this logic. Take Sundar Rao of Mumbai who weighs 89 kg. He has been trying hard to shed the extra pounds for the past 15 years. A 53-year-old chartered accountant, he religiously takes out an hour from his busy schedule for exercising and has tried all possible diet regimes he could dig out of the massive literature and studies done on weight loss. Rao has cut down on carbohydrates, increased protein intake and reduced the amount of fat he consumes. Eating out is curtailed, fruits have been added to the plate and packaged foods kicked out, but to no avail. For his height of 170 centimetres, he is 19 kg overweight; worse, he continues to gain weight.
Forty-year-old Sapna Vashista of Delhi has a similar problem. For the past six years, she has maintained a strict diet regime. One hour of yoga or aerobics and evening walks are part of her daily routine. A part-time fashion designer and mother of two, she does most of the housework. Still her weight does not dip below 72 kg. For her height of 165 centimetres, Vashista should not weigh more than 63 kg.
Both Vashista and Rao share the fate of many people who even after hours of slogging on the treadmill and giving a miss to their favourite foods are unable to shed those extra pounds. The World Health Statistics released in May by the World Health Organization (WHO) also points to the growing trouble. It shows obesity has doubled across the world between 1980 and 2008. Health experts say overeating and junk food are the biggest reasons behind the rise in obesity world over, but they cannot explain why some people are unable to lose weight when they control these habits.
Moreover, food could hardly be blamed for the increase in weight of babies below six months. Data from a research by Harvard Medical School shows the percentage of overweight infants has nearly doubled from 3.4 to 5.9 between 1980 and 2001 in the US.
Baffled researchers who set out to find the reasons say the toxins in the environment, microbes and rise in temperature also play a role in making people fat. Specifically, exposure to certain toxins, such as pesticides, emissions from vehicles and the material that the plastic bottle is made of, can lead to weight gain. Epidemiological studies suggest everyone, including those not yet born, are at risk. Most such studies have been done in the US.
For instance, a study in the US on pregnant women in New York City showed that women exposed to higher concentrations of polycyclic aromatic hydrocarbons, or PAHs, from vehicular and industrial exhaust and smoke from cigarettes, were more than twice as likely to have children who were obese by the age of seven. The study was conducted by researchers from Mailman School of Public Health at Columbia University.
The National Health and Nutrition Examination Survey in the US show similar results. When children between six and 19 years of age were tested for the presence of pesticide 2,5-dichlorophenol—commonly used in moth balls, and room and toilet deodorisers, and previously used as an insecticidal fumigant—it was found that obesity was directly proportional to the levels of the chemical in the blood. The study was published in Reviews on Environmental Health in 2011. Adults with higher levels of Bisphenol A (BPA)—commonly used in plastic bottles—were also found to be more prone to general and abdominal obesity by researchers of the Harvard School of Public Health in Boston. Till date, about 20 chemicals have been nailed for inducing weight gaining tendencies and many more may soon make it to the list. Based on their effect, the chemicals have been christened obesogens (see ‘History of obesogens’).
This does not mean diet regimes and treadmill are redundant. Whether obesogen exposure causes permanent changes in the body leading to obesity is currently under study in laboratories across the world, developmental biologist Bruce Blumberg says. Epidemiological studies give only indications. Direct studies are available only on animals. In his lab in the University of California, Irvine, US, Blumberg is analysing the obesogenic impact of a chemical, tributyltin (TBT), on mice. TBT is a biocide that is used in paints in ships to prevent the growth of algae on the hulls. It has now been banned because it leaches into the sea and affects marine life. Blumberg says, “Prenatal exposure to TBT produces irreversible effects in mice.” They get fatter despite a normal diet because TBT alters their metabolism. “So if you were exposed at a sensitive time during your life such that you have more, larger fat cells and stem cells that are predisposed to become fat cells, you will have to fight a lifelong battle against weight gain.”
Obesogens in action
Exposure to obesogens at any age can lead to obesity, but foetuses and young children have been found to be the most vulnerable. The chemicals enter the developing foetus through the mother’s blood and cause modifications in the expression of genes. These are called epigenetic changes and lead to “foetal programming”. For example, under the influence of the toxins the stem cells may be programmed to make fat cells instead of bone cells, predisposing the unborn child to be plump. A study published in the May issue of PNAS found that epigenetic changes caused by a fungicide, vinclozolin, can be passed on to as many as three generations.
In children and adults, however, the obesogenic effect of chemicals manifests as changes in metabolism through regulation of hormones. For instance, the chemicals affect the functioning of the thyroid gland, which controls metabolism. This lowers the metabolic rate and the body burns fewer calories. Other hormones affected by obesogens are leptin that regulates the feeling of satiety and resistin that reduces insulin sensitivity and leads to type 2 diabetes. These hormones are produced by the adipose tissue which till recently was believed to be just a storage space for fat. Studies have found that this tissue too has become a target of obesogens such as the fungicide, tolylfluanid. It increases the formation of fat cells and reduces leptin secretion and results in higher food intake. Another chemical, tributyltin chloride affects production of fat cells by controlling a receptor protein on the nucleus of the stem cells called peroxisome proliferator-activated receptor gamma (PPARG). It stimulates the receptor and predisposes stem cells to become fat cells.
The WHO’s health statistics reveal that women are more likely to be obese than men. This was established by a study published in the May issue of Environmental Health Perspectives where the researchers studied 665 Danish women who reported pregnancy in the late 1980s. The levels of perfluorooctanoate (PFOA)—a chemical used to make non-stick cookware—were measured in their blood. The researchers analysed Body Mass Index (BMI), an indicator of body fat, of their offspring 20 years later in 2009. They found daughters of women, who had about 6 nanogram/millilitre (ng/ml) of PFOA in their serum, had on average 1.6 kg/m2 higher BMI compared to daughters of women who had about 2 ng/ml of the chemical in their blood. They did not find the BMI difference in male offspring.
Researchers say the reason behind women being more susceptible could be that they have more fat deposits in the body. This makes them more vulnerable to the fat-soluble environmental toxins. Women have 25-31% body fat, while men have 18-25%, according to American Council on Exercise.
What is more worrisome is the fact that the obesogenic effect of the chemicals is evident even at very low doses. The same chemical at high doses becomes toxic and leads to weight loss. The obesogens do not follow the long held principle of toxicology which suggests that chemicals follow a linear curve—the larger the amount of the chemical, the more the effect on people. In case of obesogens lower doses can have more effect. This means regulators are unlikely to set appropriate safe limits for chemicals since they test them taking into consideration their linear pathway.
Frederick S vom Saal, professor at the University of Missouri in the US, who has done pioneering work on BPA, including analysing its association with obesity, says that most of the studies show that the human body carries between 0.5 and 4 ng/ml (parts per billion) of BPA in the serum. This range can be harmful, he says. The chemical can mimic estradiol and cause breast cancer even at amounts below one part per trillion, 1,000 times lower than found in the human body, he explains.
Research on obesogens is still in its infancy. Scientists are looking at all kinds of chemicals with suspicion. A decade of research has identified about 20 chemicals present in the environment as obesogens.
History Of Obesogens
Paula Baillie-Hamilton, a doctor in the UK, was having a hard time losing weight after pregnancy. Looking for ways to lose fat, she chanced upon an article on how pesticides were playing havoc with animals by inducing hormonal changes in them. It was a eureka moment. She wondered whether hormonal changes due to chemicals in the environment could be playing a role in her inability to shed pounds. A three-year-long research unearthed enough evidence.
There were studies as far back as in the 1970s to show that low-dose chemical exposures were associated with weight gain in animals. She published the results in the Journal of Alternative and Complementary Medicine in 2002. The paper was noticed by many researchers who had observed similar phenomenon in their lab animals. They initiated studies to observe the effect of the toxins on the body’s metabolism. Retha Newbold of the National Institute of Environmental Health Sciences (NIEHS) in the US tested Diethylstilbestrol (DES), used in drugs, on mice.
They were treated with 0.001 mg/kg of DES and their weight was measured after four months. While the treated mice had average weight of 40.3 grams, those not exposed weighed 30.7 grams. By 2007, the evidence was so clear that a University of California scientist, Bruce Blumberg, gave these chemicals a name—obesogens.
“There are currently about 20 chemicals that have been shown to stimulate weight gain in rodents,” says Jerrold J Heindel, programme administrator at NIEHS. These chemicals are everywhere—soft drink cans, carpets to paper money. Exposure to them is unavoidable.(Source: http://www.downtoearth.org.in/content/new-obesity, Jun 30, 2012)