Overweight and obese individuals have higher levels of stress-induced inflammation than those within a healthy weight-range, the findings showed.

"We have known that overweight and obese individuals already have chronic, low grade inflammation," said principal investigator Nicolas Rohleder, a professor at the Brandeis University, US.

"Now, it seems that when you add stress to the mix, it is a double hit," Rohleder added.

It's been long known that psychological stress can trigger biological responses similar to the effects of illness or injury, including inflammation.

For the study, the researchers measured interleukin-6 (IL-6), an inflammatory agent linked to stress, to evaluate inflammation levels in normal-weight and overweight individuals over the course of two psychological stress tests.

They classified weight based on several factors, including body mass index (BMI) and body fat percentage. Individuals with a BMI of 25 or higher were classified as overweight.

The relationship between BMI and IL-6 levels was linear; the higher the BMI, even among lean individuals, the higher the IL-6, the researchers found.

"It seems that every percentage point of body fat makes you more susceptible to inflammation," study author Christine McInnis from Brandeis University explained.

"We know that there are serious diseases associated with obesity. Now we are one step closer to understanding how and why," she added.

The study appeared in the journal Brain, Behavior and Immunity.

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