Planning to run a marathon? Be careful what you eat while training.

A diet high in simple carbs and saturated fats can weaken the cartilage in your knees and hips, according to a study published in Scientific Reports.

Fatty foods like butter, palm oil, and animal fat in tandem with simple carbs (aka junk food) can trigger the onset of osteoarthritis.

"Saturated fatty acid deposits in the cartilage change its metabolism and weaken the cartilage, making it more prone to damage," study author Yin Xiao said in a press release. "This would, in turn, lead to osteoarthritic pain from the loss of the cushioning effect of cartilage."

Antioxidants and anti-cholesterol drugs may slow the progress of joint damage caused by fatty acids, the researchers note. Take note before going out for a run. And use these strategies for pain-free running.