How Chemicals May Promote Stress That Leads to Obesity
Pollution, stress and weight gain reinforce each other in negative ways, creating a cycle that makes obesity more likely, according to a study published this month in Obesity Reviews
Chemicals from plastics to pesticides may worsen the body’s stress response in ways that cause excessive weight gain, according to what researchers say is the first systematic review to investigate the link between pollution, stress and obesity.
Obesity is a risk factor for chronic conditions such as depression, Type 2 diabetes, cardiovascular disease and cancer, and is one of the leading causes of death worldwide.
The findings, published this month (Jan. 17) in Obesity Reviews, suggests that pollution, stress and weight gain reinforce each other in negative ways, creating a cycle that makes obesity more likely.
The associations, however, depend on sex, age and pollutant type, among other factors.
Researchers focused on 42 studies — with 8,500 human and nearly 3,200 animal subjects — that investigated the effect of a range of pollutants on fat cell growth (adiposity) in humans, animals and cells, as well as how the body and mind respond to stress.
Pollutants included:
- Chemical preservatives like parabens.
- Halogenated aromatic hydrocarbons, such as flame retardants.
- Heavy metals such as cadmium, nickel, mercury and lead.
- Pesticides, including the herbicides glyphosate and atrazine.
- Plastics (phthalates).
“We provide evidence that in most articles, pollution is responsible for stress-response disruption and results in weight gain,” the researchers say.
This cycle may occur as:
- Pollution increases stress: Air pollution and toxins could activate the stress response, raising levels of the stress hormone cortisol. Cortisol helps to maintain blood pressure, immune function and the body’s anti-inflammatory processes.
- Pollutants also disrupt metabolism: Endocrine-disrupting chemicals like phthalates (used in plastics) and perfluorooctanoic acid, or PFOA, activate natural processes in the body — specifically, key signaling pathways (PPARγ and AhR) — that increase fat cell growth and fat storage.
- Stress contributes to obesity: High cortisol levels sparked by stress increase appetite and cause fat cells to grow and multiply, leading to overeating and fat accumulation. Chronic stress may also erode the long-term ability of hormones like cortisol (glucocorticoids) to manage stress and inflammation and help the body process toxins.
- Obesity reduces the body’s ability to clear pollutants from the body: Fat tissue stores toxins, making it harder for the body to detoxify and worsening their hazardous effects over time. Obesity can also impair the activity of certain enzymes, slowing the body’s ability to eliminate harmful substances.
The findings come amid growing evidence that pollution, stress and obesity are closely linked through biological and environmental mechanisms that affect metabolism, hormones and fat storage.
One recent study showed that exposure to “forever chemicals” may be linked to childhood obesity.
Another suggested that prenatal exposure to chemicals in food packaging and plastics may increase young children’s body fat. Only a limited number of studies, however, have investigated these three variables together, the researchers say.
The researchers say differences between the studies they reviewed might be due to the body’s natural daily cortisol cycle, among other variables, and how it is measured. Hair cortisol reflects long-term stress levels, for instance, while blood cortisol shows short-term or immediate stress levels.
More research is needed, they conclude:
“Considering the rising exposure of global populations to pollution, psychosocial stress, and over-nutrition, further research is warranted to reduce our environmental footprint and tackle stress and obesity at the population level.”
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