True GERD is caused by problems with the lower esophageal sphincter, the band of muscle that connects the esophagus (your throat) with the stomach. GERD is not the same as indigestion gone evil :-)

With GERD either the sphincter muscle works well/properly or it does not. If it does not, the stomach acids can get up to the esophagus and that isn't protected from the acids like the stomach is.

Lifestyle doesn't cause GERD but adjusting it can sometimes help. Some triggers for GERD are:

Certain foods or drinks
Smoking
Being overweight
Eating too much
Bending over after eating
Lying down less than 3 hours after meals

I don't know why one would bend over after eating? I guess exercising that includes touching one's toes is out? But the way things work is the sphincter opens to let in food; so, it closes at a certain time but it might get in the "habit" of not. It could be, freewill, that having an ED, your stomach has decided over time to leave it open, hoping you'll eat more? Or, like other muscles, it has lost tone? Too, your body might be producing stomach acids out of proportion to the amount you can now eat; kind of like how more sharks than meat can show up at the scene? It's harder for your stomach to shut down some of that acid production and/or your sphincter muscle to close.