There can be many sins in food, especially when eating in restaurants, because we don’t know the state of the cook, nor the people handling the food, or the bad energy coming from other people eating there, or even the people walking past the restaurant. The same applies to fast-food.
We also don’t know about farming methods used, how harvesters were treated, nor what happened in the market. So there are many ways for sins to come onto food.
Cooking with Wudu and reciting the Opening Verse of the Qur’an and the Declaration of Unity (Kalimat at-Tawhid) before eating, removes all bad energy. Keep Wudu when cooking; then also keep Wudu when eating. This is the habit of the Friends of God (Awliyaullah), which they expect from any follower who wants to progress on the Way.
From Mawlana Shaykh Hisham.