Instructions
Leave various types of food out for the ants to eat. Try sweets, proteins and carbohydrates. Leave them out side-by-side where you notice ants. Place the same amount of food each type of food.
Check the food every couple hours to see how much of each is gone. Take note of what type of food goes first to see whether the ants have a preference for taste or ease of movement -- they might go for the lighter food first.
Take note of whether the ants went for the more nutritious food first and whether they went for all food items. You may also note whether more ants became aware of the food after several days.
Be certain it is only the ants that are taking the food. You may have other insects and animals around. This means you will need to monitor the food closely.
See if the ants are as attracted to liquid sweets such as cola, or protein-rich liquids such as milk. These beverages can't be brought back to the colony so experiment to see if they prefer food that can be carried back.