Dates (Phoenix dactylifera) depending on how you eat them can either cause weight loss or weight gain. Dates are grown relatively across Africa and the Middle East. They contain sugars, fibres, fatty acids, calcium, just to mention a few. This sweet fruit is highly nutritious and can provide necessary nutrients just enough for weight loss and weight maintenance.
However, when eaten in excess, the sugars, especially fructose can be converted to fats in the body and this would mask the effect of dietary fibres and other nutrients that could have been otherwise used to aid proper digestion.
Since you want to add weight, you should consider eating well more tthan six dates daily. You can also spice it up with other rich fruits like avocados and olives. It works well with cooked food too to like rice.