Diet Pepsi contains zero calories and is the Taco Bell item that contains the fewest calories, according to Tacobell.com. As of 2015, the lowest-calorie taco is the Fresco Chicken Soft Taco with 140 calories, and the lowest-calorie burrito, the Fresco Burrito Supreme with Chicken, has 340.
Taco Bell's Fresco menu contains signature items that substitute more calorie-rich toppings such as cheese with pico de gallo salsa. Other examples include the Fresco Crunchy Taco, the Fresco Soft Taco, the Fresco Grilled Steak Soft Taco and the Fresco Burrito Supreme with Steak. Each item contains fewer than 350 calories and less than 10 grams of fat. Other Taco Bell items also can be ordered Fresco-style.