Have you ever noticed that healthy people bounce back from illness or injuries quicker than overweight people?  That is because being fit and trim has profound effects on one's immune system and the ability to repair.  

This new study found the opposite to be true for obese folks.

The researchers found that the obese mice had a compromised immune response to the bacteria, which made the animals more susceptible to the infection.

Amar's group also looked at the animals' white blood cells, which are the main line of defense against infection. The white cells of obese mice had lower levels of an important signaling molecule, and some of the genes that fight inflammation were altered, the researchers found.

Why obesity has this effect isn't clear, but the researchers think it may involve a signaling pathway that controls a protein called NF-kB. Alterations in this protein may be caused by constant exposure to food, Amar explained. "At some point, the body doesn't respond properly to infection," he said.