We all have body fat. It's necessary for proper body function. While a healthy percentage of body fat varies greatly, according to the American College of Sports Medicine a healthy range for women under 40 is 20-35%, for men 8-22%. (The ranges change for those over 40 and for fitness standards.)

But a recent study reveals that one fat cell isn't necessarily like another. In obese people, fat cells appear "sick."

Compared to fat cells taken from lean people, the fat cells from obese people were deficient in several ways. For example, the endoplasmic reticulum -- which helps cells synthesize proteins -- was stressed in the fat cells of obese people. This stress of the endoplasmic reticulum could inhibit or change the body's production of protein and could lead to insulin resistance (a contributing factor for obesity).

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