OBESOGENSCan chemicals make us fat?
- info848287
- Apr 20
- 4 min read
The answer is a definite yes for some chemicals, as evidence from trials shows us that some drugs do tend to increase obesity as a side effect. Well-known among these are the birth control pill and some antidepressants. Because drugs have to undergo trials to get on the market, we have strong evidence about their effects and side effects.
For many other chemicals in our food and our environment, it’s a “definite maybe”. Because chemicals in foods and air pollution don’t have to be tested rigorously, indeed some not at all, we have far less robust information about their effects on us. We have evidence from observational studies, which is insufficient to demonstrate causality on its own. However, when we include research on animals, we see increasing evidence that some of these chemicals seem to encourage weight gain, despite our best efforts to cut calories and get good exercise. Some of these substances may also predispose us to overeating or binge eating, sometimes by design! These chemicals may help explain the recent large increases in obesity, in all ages in the same time frame. They are called obesogens: things that generate obesity.
Some obesogens affect the gut microbiome or the gut itself: many people have seen the experiment where a slim mouse became obese when it’s microbiome was changed to that of an overweight mouse.
Many other obesogens are endocrine disruptors: they alter the function of our body systems that regulate appetite, satiety, weight gain, fat development and fat distribution. This often triggers a tendency to diet-induced weight gain and difficulty losing weight. And this all happens below our conscious awareness.
By 2023 about 1000 chemicals were designated as endocrine disrupting chemicals (EDCs), some of which can act at very, very low concentrations. And they don’t just affect fat cells: some appear to have effects on the gastrointestinal tract, the pancreas, the liver, muscle tissue, and the brain.
Several phthalates are known endocrine disruptors. They are chemicals used primarily as plasticizers to increase the flexibility of plastics, including those used to wrap foods. This is why food is a major route of exposure to phthalates, and we recommend not allowing them to touch your foods. These same plasticizers are also used in some dishwasher and laundry pods, and can leave residue on your plates and cutlery. Unfortunately they aren’t the only likely hormone disruptors in dish-cleaning products: the fragrances and colourings, as well as rinsing agents, are also suspect.
These chemicals aren’t considered to be the only cause, but may be an important factor predisposing people to obesity. They are likely part of the reason ultra-processed foods*, which contain more synthetic chemicals (as well as more calories), are strongly associated with increased obesity. They may also help explain why the rise of obesity occurred across multiple age groups at the same time, after ultra-processed foods became so prevalent. It is a shocking fact that a UNICEF report published in September 2025, stated that we now have more obese children in the world that underweight ones, for the first time in recorded history.
The link between increased chemical production and the rise of obesity was formally hypothesized in 2002 by Paula Baille-Hamilton. Exposure to these chemicals has been shown to affect us throughout our lifespan. A randomized controlled trial in 2019, in which people were allowed to eat as much or as little as they wanted, found that the consumption of ultra-processed food resulted in increased caloric intake, and a 2-pound weight gain within two weeks. This compared with a 2-pound weight loss in those eating an unprocessed food diet! This was despite the foods being matched for nutrient density, macronutrients, and palatability. So these chemicals can affect us at any time of life.
But the effects of obesogens are more pronounced during certain windows in development, although their obesogenic effects may not be seen until puberty or beyond. In utero, early childhood and adolescence, epigenetic changes** can increase sensitivity to weight gain later in life. For example, a 2018 meta-analysis of 6076 participants concluded that exposure to PFOA (a “forever chemical”) in utero or the first year of life, is associated with an increased risk for childhood obesity. And in animal studies those epigenetic changes have been passed down over generations.
Preliminary screening has suggested possible metabolic disrupting potential of the widely used synthetic colour additives Red 40, Yellow 5, and Yellow 6***, the preservative benzoic acid, and the flavourings ethyl butyrate and methyl salicylate. Other potential obesogens added to our food, and for which further assessment is necessary, include:
BPA
3-butylated hydroxyanisole (3-BHA)
caffeine
di-2-ethylhexyl phthalate (DEHP)
dioctyl sodium sulfosuccinate (DSS)
monosodium glutamate (MSG)
parabens
perfluorooctanoic acid (PFOA)
propionate
Clearly the obvious way to reduce your exposure to this multitude of chemicals, whether some or all are found to be obesogens, is to eat fresh, organic foods as much as possible, and avoid wrapping food in stretchy plastic wrap.
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