When shooting food for a restaurant, I use available light and a reflector whenever possible as it gives a natural look to the food. Food is a natural subject, consisting of elements taken from nature and the veg garden, so I believe that shooting in natural light is the best way to get this feeling of nature across in the final image.
I find that the best spot in a restaurant to shoot the food is by a window, with the light coming from one side, as side light brings out the texture in food – also try lighting from behind the food to create ‘blown out’ highlights and a nice feeling of light. Generally you should avoid direct sunlight, as this is just too strong and will give you an image with very high contrast.
Once you have found some lovely soft directional window light, you may find quite a strong shadow on the opposite side of the food. Unless you are in the middle of a nice meal and dont want to create a scene, use a reflector on the other side of the dish to bounce light back into this shadow area.