Image source: Chipotle Mexican Grill.

Chipotle Mexican Grill (CMG 1.11%) prides itself on offering a healthier alternative to fast food, but a recent study seemed to challenge this claim after finding that entrees at fast-casual chains like Chipotle have an average of 36% more calories than entrees at fast-food chains such as McDonald's (MCD 0.49%) and Wendy's (WEN 1.60%).

The issue, however, is that the study doesn't actually support this contention. Nor, to be fair, does it claim to. According to its conclusion:

Although fast-casual entrees contained more calories than fast-food entrees in the study sample, future studies should compare actual purchasing patterns from these restaurants to determine whether the energy content or nutrient density of full meals (i.e., entrees with sides and drinks) differs between fast-casual restaurants and fast-food restaurants.

Here's what the authors mean: While it's true that the typical entree at Chipotle has more calories than entrees at McDonald's and Wendy's, the story is different once you consider add-ons. There's a reason, after all, that McDonald's employees have long been trained to ask: "Do you want fries with that?"

Consider this: A burrito at Chipotle with a flour tortilla, chicken, white rice, black beans, salsa, cheese, and lettuce packs in 940 calories. Adding sour cream increases the total by 115 calories, and guacamole boosts it another 230. For the sake of argument, then, let's say that there are 1100 calories in a typical Chipotle burrito. (NOTE: The breakdown in the image below includes all of the fixin's, so to speak.)

Data source: Chipotle Mexican Grill. Chart by author.

If you compare this to a standard McDonald's entree, say a Big Mac or a Quarter Pounder with Cheese, it's clear that the study is onto something. Each of these entrees has 540 calories. And the same is true at Wendy's, where a Quarter Pound Single with Cheese has 590 calories.

But what's important to keep in mind is that, unlike at Chipotle, I think it's fair to say that most people who go to McDonald's and Wendy's order more than a single item. I typically order two -- though, being the cheapskate that I am, I also stick to items on the value menu. I usually get two double cheeseburgers, which adds up to 880 calories. That's 60 calories more than my usual burrito order at Chipotle.

The same is true when you factor in snacks and sides at McDonald's and Wendy's. A medium fries at McDonald's adds 340 calories. And a large order adds 510 calories. The range at Wendy's is from 320 to 530. When you include that with an entree, you get a total of between 850 to 1100 calories. Based on calories alone, in turn, eating a burrito at Chipotle is essentially no different than getting a meal at McDonald's and Wendy's.

Consequently, while the results of the study initially seemed to undermine Chipotle's value proposition, which is one of the foundations of the chain's success, it's clear that there is more to this story than meets the eye.