For the people who struggle with temptation of food, taxing fast food items that are considered to be the most deadly foods due to their high sugar and fat content might make people think twice before they order these tasty meals. Even though fast food items are relatively cheap, it is still cheaper to cook at home.
Buying fruits and vegetables at the store and then preparing a meal at home would be far cheaper for the average family of four then spending money for each meal. Of course, this depends on the meals that are being served. Taxing fast food might cause some people to not afford to buy these items and then they will get into a habit of cooking for their family instead.