There are a lot of research about the risks of a restaurant as a business (read Why Some Restaurants Fails as Business Idea).
However the restaurant business is still an attractive idea for make money. As the market is already saturated maybe you should think to focus your restaurant in specialized food.
Look these ideas about it:
1. Food Allergy specialist. Here there are several alternatives depending on the type of allergies. You should do an investigation of population density in your city that suffers from allergies so determined to give more prominence to a product over another.
2. Food Diabetic specialist. The importance of this market is indisputable. On supermarkets you can find special lines of this kind of food.
3. Food organic specialist. This item is perhaps one of the most exploited, but the suggestion is to distinguish the presentation of the other specializations.
4. Food specialized athletes. This item is also over-exploited but more from the perspective of vitamins and supplements. You can give a new approach with special recipes provide effective counseling with a nutritionist.
5. Food for weight loss specialist. Here you need the advice of a nutritionist to do business differently. You could sell not only products but also how to use them together to achieve goals.
6. Food specialist to reduce certain pathogens in the body. One example of this is people with high cholesterol that should to do special diets. So there are several diseases that require special diets. Visit your city clinics and find out where they will be more successful.