People who are overweight have a greater risk for stress-related diseases like type 2 diabetes, cardiovascular disease and cancer, according to a new study.

It's long known that psychological stress can trigger biological responses similar to the effects of illness or injury, including inflammation. While normal inflammation is an important part of our body's healing response, runaway inflammation can contribute to chronic and life-threatening diseases.

Researchers from Brandeis University in Massachusetts observed that overweight and obese individuals have higher levels of stress-induced inflammation than those within a healthy weight-range.

"We've known that overweight and obese individuals already have chronic, low grade inflammation," Nicolas Rohleder, the study's principal investigator, said in a statement. "Now, it seems that when you add stress to the mix, it's a double hit."

For the study, 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.

Researchers found that the relationship between BMI and IL-6 levels was linear -- the higher the BMI, even among lean individuals, the higher the IL-6.

"It seems that every percentage point of body fat makes your more susceptible to inflammation," researcher Christine McInnis said.

With about two-thirds of Americans classified as overweight, and worldwide obesity rates doubling since 1980, understanding the health risks of obesity could not be more important, according to McInnis.

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

The findings were recently published in the journal Brain, Behavior and Immunity.