With a meaty taste and few calories, portobello mushrooms make a healthy, flavorful alternative to hamburger patties and other traditional sandwich fillings. That said, a lean portobello sandwich can quickly turn into a calorie bomb if you pile on fatty toppings like cheese, mayonnaise or pesto sauce. Keep your lunch light by using reduced-fat cheese and topping your mushroom with fresh vegetables like lettuce, tomato and onion instead of the heavier alternatives.
Calories in Your Sandwich
One cup of grilled portobello mushroom slices contains just 35 calories. A hamburger bun has about 117 calories, while two slices of whole-wheat bread contain about 161 calories, so a plain sandwich may contain 152 or 196 calories, respectively. The calorie count will climb, of course, as you add toppings. A particularly rich recipe from "Fine Cooking" that includes fatty ingredients like mozzarella, Parmesan cheese and mayonnaise contains about 540 calories per sandwich.