(CNN) Plant-based diets have been associated with many health benefits, including a reduced risk of obesity, heart disease and Type 2 diabetes. So it might naturally follow that vegetarian fast food, which is inherently plant-based, would be more nutritionally appealing than its traditional relatives.
The truth is that, although the notion works in many cases, it's not a guiding food principle you can count on.
"Just because a restaurant or fast food menu item says it's vegetarian or vegan, it doesn't mean that it's automatically 'healthy.' It can have just as much, if not more, calories, saturated fat and sodium as non-vegetarian options," said Sharon Palmer, a registered dietitian and author of "Plant-Powered for Life."
It makes sense. After all, ingredients contribute calories, whether plant-based or not. And while fiber and protein can be higher in vegetarian meals, thanks to plentiful amounts of beans, vegetables and whole grains, so can things such as saturated fat and sodium, depending on how the food is prepared (fried vs. grilled, for example) and the amount of cheese and condiments a meal contains.
"Vegetarian and vegan food options that are deep-fried, covered in cheese or creamy sauces and piled over huge portions of fries, rice, wraps or breads may not be the healthiest option on the menu," Palmer said.
For example, Veggie Grill's Fala-Full sandwich -- two pitas filled with falafel, hummus, pepperoncini and schug and tzatziki sauces, with a side of tabbouleh -- has 1,100 calories, 10 grams of saturated fat and more than a day's worth of sodium (2,380 milligrams). That's more than double the calories, 2½ times the sodium and the same amount of saturated fat as a McDonald's Big Mac. (A Big Mac has 540 calories, 950 milligrams of sodium and 10 grams of saturated fat).
On the other hand, the Veggie Grill's grilled "chickin' " sandwich made with soybean, wheat and pea-based protein has only 530 calories, 900 milligrams of sodium and 3 grams of saturated fat.
The takeaway: Menu items can vary widely, depending on the type and amount of ingredients used, and sauces and deep frying will contribute extra calories, fat and sodium.
Speaking of burgers, the Amy Burger at Amy's Drive Thru -- a meat-free fast food restaurant with ambition to expand to other markets, owned by the company that makes Amy's vegetarian supermarket foods nationwide -- includes two veggie patties with cheese and sauce. The burger has 770 calories, 10 grams of saturated fat, 33 grams of protein, 9 grams of fiber and 1,420 milligrams of sodium. Veggie Grill's Beyond Burger with a single patty has more saturated fat (13 grams) and the same amount of sodium as Amy's.
Surprisingly, the McDonald's Big Mac has fewer calories and less sodium than both veggie burgers, and it has less saturated fat than Veggie Grill's single-patty veggie burger (10 grams).
Still, both veggie burgers have more fiber, and Amy's has more protein than Mickey D's Big Mac, which can keep you feeling full. Plus, Amy's ingredients -- aside from being meat-free -- are locally sourced and organic, all of which may be more important than nutrition numbers, especially for those who don't need to be counting them.
Veggie Grill's Mondo Nachos, for another example, made with "chickin' " and "queso chorizo" sauce, have more than 900 calories, 7 grams of saturated fat and almost 1,600 milligrams of sodium. By comparison, Taco Bell's BellGrande nachos with beef have fewer calories (760), slightly less saturated fat (6 grams) and less sodium (1,290 milligrams). Once again, however, the Grill's has more protein and fiber.
It's important to remember that not all beef tacos are created equal. Del Taco's queso loaded nachos with beef top the list, with more than 1,000 calories, a day's worth of saturated fat and over 2,000 milligrams of sodium.
When it comes to mac and cheese, both Amy's Drive Thru and Veggie Grill's vegan versions have less sodium, more fiber and a lot less saturated fat than Panera's small traditional version, though Panera's packs much more protein.
As with other menu items, the nutritional contributions of salads are a direct reflection of the ingredients used, so it's difficult to make broad generalizations. For example, Veggie Grill's All Hail Kale salad and Amy's Super Salad with tofu, hummus, quinoa and roasted pumpkin seeds are nutritional winners, but a falafel-containing salad at Veggie Grill is going to have a lot more calories, sodium and fat.
Then again, that's really the takeaway message for all menu items, whether they are vegetarian, vegan or neither. That is, a meal is only as healthy as its ingredients.
So just because a food is "vegetarian" or "vegan" doesn't guarantee that it's a nutritionally superior option. French fries may be vegetarian, but that doesn't mean they should fill your plate on a regular basis.
Palmer recommends looking for options that include plenty of vegetables, such as salads, bowls or wraps; whole grains, such as quinoa or whole-grain bread; and simple protein options, like beans or a veggie burger patty. She also advises "going easy on sauces, creams and cheeses," which makes good health sense, whether you choose to eat vegetarian or not.