Not in the gym—in your blood. Iron helps red blood cells deliver oxygen to your body’s tissues. When you’re running low on iron, your whole body feels it. It often makes you very tired, and can also cause headaches, yellowish skin, brittle nails, hair loss, and general overall weakness. 

Your internist can check your iron levels with a simple blood test, but if you turn out to be anemic you may need to see a GI specialist. “Iron deficiency anemia can often be due to chronic, unseen blood loss in the GI tract from things like colon cancer, stomach cancer, ulcers, inflammatory bowel disease or superficial blood vessels called angiodysplasia,” says Burney.

Related: 6 Foods GI Doctors Avoid

The article 6 Signs You Need To See A GI Doctor ASAP originally appeared on Prevention.