During training, intra-abdominal pressure is increased. This exerts force on the stomach, pushing its contents upward. If the LES is weak, it can't provide enough resistance against the back flow and an acidic, burning sensation occurs. If you have reflux, it is important to stay away from foods that increase LES pressure. You also should stay away from coffee and other sources that increase acid production.
Protein is actually a double-edged sword.
On one hand, higher protein consumption can be beneficial since this helps to reduce LES pressure. Thus, for mild cases, a high protein intake is advisable while in severe cases, a more moderate consumption is warranted. You should always have something to eat within a few hours of a workout. Training on an empty stomach can cause a dramatic drop in blood sugar, often resulting in feelings of dizziness and fatigue. Inevitably, your energy capacity will be limited and performance will suffer.