Writing in the International Journal of Obesity, the scientists explain the substances in question are man-made chemicals called persistent organic pollutants (POPs), which are normally found in pesticides and food packaging.
These pollutants get into your system in minute quantities via the food you eat and are stored in your body's fatty tissues, where experts believe they remain harmless. But when you lose weight and those fatty tissues break down, the POPs are released into your bloodstream.
Once in your bloodstream, the Korean researchers claim POPs could build up and cause problems such as type 2 diabetes, high blood pressure, coronary heart disease and rheumatoid arthritis.
The researchers studied more than 1,000 volunteers and recorded levels of POPs in their blood. The people who lost the most weight over ten years - around 10kg or more - had the highest concentration of the pollutants in their blood compared to those who either gained or maintained a steady weight.
However, the Korean team admits nobody yet knows the amount of POPs you need in your system before they start causing problems. So for now, it shouldn't put anyone off losing weight - especially if your weight is a potential health risk.
Have you ever used an excuse not to go on a diet? We'd love to hear about it.
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