Long-term weight loss releases industrial pollutants stored in fatty tissue into the blood, South Korean researchers have found.
According to a study published in the International Journal of Obesity, compounds called persistent organic pollutants (POPs), normally stored in fatty tissue, are released into the blood stream when fat is broken down, researchers at Kyungpook National University found.
Once released, POPs can reach the vital organs and can be a contributing factor to diseases such as heart disease, type 2 diabetes and hypertension.
"We are living under the strong dogma that weight loss is always beneficial, but weight gain is always harmful ... but we think that increased [pollutant] levels [in the blood] due to weight loss can affect human health in a variety of ways," lead researcher Duk-Hee Lee told Reuters.
Lee and an international team of researchers studied 1099 participants in the US, analysing the concentration of seven harmful compounds in their blood.
Those who lost most weight over the course of 10 years had higher concentrations of the compounds compared to those who gained or maintained a steady weight, even after scientists factored in age gender and race.
"There is emerging evidence that POPs ... are not safe. POPs [are] linked to type 2 diabetes, hypertension, coronary heart disease, rheumatoid arthritis, periodontal disease," Lee said.
Which is worse?
"This finding may suggest that long-term weight loss may increase POP levels in blood, but more studies are required in order to determine whether this translates to a higher risk for certain diseases," Dr Cassy Richmond told Health & Wellbeing.
"In the meantime, there is evidence that being overweight or obese may increase your chances of developing coronary artery disease, hypertension, stroke and type 2 diabetes," she said.
"It can also increase your chances of having such conditions as sleep apnoea, osteoarthiritis and gallstones. It is therefore advisable to keep within a healthy weight range (BMI 19-25)."
According to the US' Environmental Protection Agency, persistent organic pollutants work their way through the food chain by accumulating in the body fat of living creatures and become more concentrated as they move from one creature to the next.
Those most at risk of being exposed are people whose diets include large amounts of fish, shellfish, or wild foods that are high in fat.
In 2001, the US joined 90 other countries and the European Community to sign the United Nations' Stockholm Convention on Persistent Organic Pollutants. Under the treaty, participating countries agreed to reduce or eliminate the production, use, and/or release of 12 key POPs.