Yes, protein powder can be taken on an empty stomach. There is no clear evidence suggesting that taking protein powder with or without food has a significant impact on its effectiveness or digestion.
However, some people may experience gastrointestinal discomfort or bloating when taking protein powder on an empty stomach, especially if they have a sensitive digestive system. In this case, it may be helpful to consume protein powder with a small amount of food, such as a piece of fruit or a handful of nuts, to help minimize discomfort.
Overall, the best approach may vary depending on individual preferences and digestive tolerances. It's always best to listen to your body and adjust your protein powder consumption as needed.