Is our environment affecting our weight?

Reference article: Heindel, J.J. and Blumberg, B. (2019) Environmental Obesogens: Mechanisms and Controversies. Annu Rev of Pharmacol Toxicol. Vol. 6, Issue 59; pages 89-106. doi: 10.1146/annurev- pharmtox-010818-021304.

Challenging Experiences, Challenging Data

I’m sure you know someone who has struggled with their weight as long as you can remember. Maybe you have, personally. For a long time, weight gain was considered a simple matter of energy balance — a straightforward relationship between calories eaten and calories burned. Genetics have been recognized as contributing to weight gain, but still the equation has been considered relatively straightforward. If you’ve ever agonized over your weight, though, you probably have felt that it isn’t that easy. You may have cut calories and started working out but with very little weight loss. You may have been discouraged, or you may have felt alone.

As it turns out, you’re probably right — weight loss isn’t just a simple matter of energy balance, and you may be fighting against more than you know. Since the 1960’s, the commonness of obesity has risen dramatically in the US, from 13.4 to 35.7%. That’s more than double. At the same time, however, physical activity during free time has risen. That alone seems to suggest there may be more to the equation. Because of this (and similarly challenging findings), scientists began to investigate the role of developmental conditions on weight gain. Through this work, certain chemicals have been identified as obesogens (or those that boost obesity risk).

Figure 1: For many, weighing themselves is a daily cause of anxiety as they struggle to maintain a healthy weight. Source: https://commons.wikimedia.org/wiki/File:Feet_on_scale.jpg
What are we Fighting Against?

There is a theory that we have a natural set point for our weight, and that our bodies should automatically regulate their weight around that point. Our brains receive metabolic signals from throughout our bodies and use the data in weight regulation. This promotes stability over time; if we lose weight when we get sick, or gain a bit because we eat a lot of pumpkin pie around Thanksgiving, we should gain or lose the extra few pounds quickly and return to our normal weight. Unfortunately, this theory is supported by the fact that most obese people (many studies say more than 83%) who lose a large amount of weight while following a strict diet/exercise plan end up gaining it back in just a few years. So, the question, then, is what determines the set point?

We each have an endocrine system that produces hormones involved in regulating things like growth, sexual development, and metabolism. Certain chemicals can disrupt the normal function of the endocrine system and interfere with hormone action. These chemicals are known as endocrine disrupting chemicals (or EDCs). A little over 10 years ago, the obesogen hypothesis, which proposes that EDCs exists that may influence fat cell formation and obesity and could be contributing to the obesity epidemic, was introduced. It is thought that during fetal/early development and certain life stages we are more sensitive to the influence of these obesogens.

There is still much to be understood about the mechanisms by which individual obesogens affect obesity risk, but there are a few that have been described in detail. For example, people are often exposed to tributylin (TBT) through dietary sources. In studies involving mice and humans, TBT has been found to both promote the production of fat cells and to shift lipid balance. Additionally, prenatal nicotine exposure has been shown to effect the set point of body weight in rats, and exposure to bisphenolalynine (BPA) during gestation and lactation resulted in female adult mice with lower activity levels and energy expenditure. More work in animal models has shown that exposure to obesogens during development may result in greater weight of fat deposits and greater number and size of fat cells. Recent work with model organisms suggests that the effects of obesogens may even be passed on through multiple generations. It is important to note, however, that the effects of obesogens in humans are likely quite complicated. We know that factors including a person’s microbiome, genetics, exercise habits, diet, medication, individual variation, etc. may all influence weight gain and could interact with obesogens in a variety of ways, so much more work must be done before we fully understand how these chemicals influence susceptibility to obesity.

Figure 2: Graph showing the prevalence of obesity in US children by age-range. Source: https://commons.wikimedia.org/wiki/File:CDC_Prevalence_of_Childhood_Obesity.jpg
What Now?

Though it’s frustrating that there may be even more working against our ability to achieve and maintain a healthy weight than we previously realized, the first step to overcoming barriers is understanding them. So far, roughly 50 chemicals have been recognized as obesogens, but more research needs to be done to determine how these obesogens work. As the effects of obesogens are better understood, we will be able to better avoid exposure and/or to lessen their influence. In the meantime, remember that though obesogen exposure may make it more difficult for some people to lose weight than others, diet and exercise are still beneficial. Healthy weight is still attainable! I hope you take this information as encouraging rather than frustrating — it may be more difficult for you to lose weight, but even the influence of obesogens can be overcome.

 

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Riley Lovejoy

Riley Lovejoy

I am a PhD candidate at the University of Alabama, where I completed a Master’s degree in 2017. My current research focuses on biological invasions of ecological communities, using freshwater plankton as a study system. I believe science is for everyone, and love connecting others with topics they can become passionate about. Because of this, I founded an organization called Delta Tree Initiative that introduces middle and high school girls to STEM research and careers. If I’m not at a microscope, in a pond, or doing outreach, you can likely find me hiking, baking, or spending time with family and friends. Instagram: @love.joy.science

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