For future food supply, getting data from the current food importation and domestic food production, and analyzing them with respect to the government policies on food production and importation will give you sufficient information.
For food demand, investigate the current rate of hunger, malnutrition, nutrition status, economic development, relevant government policies, food consumption pattern, eating habit, level of poverty, and other relevant data.
Also get information on the future predictions about the above listed factors.
You may need to get quantitative data on the above information and model them using relevant statistical or mathematic tools/software to get more future information