The key word here is moderate. Vigorous exercises like running can agitate your digestive tract and provoke reflux, but incorporating moderate, low-impact exercises such as walking is actually beneficial (and it keeps you upright, allowing gravity to aid digestion). Exercise can also help you lose weight, which can dramatically reduce the severity of heartburn. To minimize the risk of symptoms, wait at least two hours after eating to work out; also avoid sports drinks, which may aggravate reflux due to their acidity. If you're a beginner, start slow and build up to at least 30 minutes of walking most days of the week.