A junk food diet is clearly not healthy. Burgers widen our waistlines, raise our cholesterol levels and tighten our arteries. But scientists now think that even before it shows up as additional pounds on the scale, junk food is changing our bodies in other, surprising ways. It’s actually a form of malnutrition that could be making our immune systems attack our own bodies.
In a recent study  published in the Journal of Immunology, scientists at Australia’s University of New South Wales investigated a typical western diet—one that’s high in saturated, monounsaturated and polyunsaturated fatty acids. Specifically, they looked at the diet’s impact on immune cells called T lymphocytes, or T cells.
The researchers fed mice a high-fat diet for nine weeks to see what effect it would have on the T cells before the mice gained weight. The results surprised study leader Abigail Pollock. “Despite our hypothesis that the T cell response and capacity to eliminate invading pathogens would be weakened we actually saw the opposite: the percentage of overactive T cells increased,” she explained .
This might sound great, but having more T cells doesn’t necessarily mean your immune system is stronger. In fact, when the immune system goes into overdrive, it attacks healthy parts of the body, resulting in autoimmune diseases like type 1 diabetes, rheumatoid arthritis and inflammatory bowel disease.