If you’ve eaten at Chipotle, you know its sustainability story. If you haven’t, take a tour of its website and you’ll learn about how vegetables are grown in healthy soil, how it's removed GMOs from its menu, how it's taken a stand against growth hormones and antibiotics in milking cows and how it's allowing pigs to "root and roam" instead of being caged up.

Chipotle has done a great job of committing to this approach, developing the message around it and building its brand on it. It makes for a strong and easily recognizable differentiator in the industry.

It also creates a set of challenges — the kind of challenges that come when any company puts a stake in the ground and has to hold itself accountable to the stand it's taken. In reality, taking a stand on sustainability is no different from taking a stand on quality or innovation. In order to maintain any brand position, you have to defend the core attribute upon which it’s built.

So this is a story about doing exactly that — it just so happens it’s a story about defending a claim of sustainability.

The first challenge arose around Chipotle’s "Pork Protocol." After discovering that one of its major pork suppliers was not raising its pork to Chipotle’s animal treatment standards, it pulled the pork from its menus, creating a carnitas shortage. It took nine months to get pork back on the menu at most of its restaurants.

Although I’m sure it was painful, Chipotle did exactly the right thing here. Its efforts reinforced to the public that its brand is pure — that its commitment to the humane treatment of animals and sustainable farming practices isn’t just some nice-sounding ad copy. It’s real. And its actions spoke louder than words, demonstrating transparency and a commitment to fix anything out of alignment with its brand message of "food with integrity."

It also tells consumers it checks the veracity of its own story, and because it was being proactive, it further strengthened my belief in its commitment.

You may have seen the second challenge the company is dealing with: the "Chubby Chipotle" campaign. The Center for Consumer Freedom, a food industry lobbying group, has developed a campaign asserting that eating two Chipotle burritos a week could cause someone to gain 40 pounds.

A spokesperson from Chipotle labeled these ads a smear campaign and I’m inclined to agree (the campaign is run by a guy who built a career lobbying on behalf of food companies against health initiatives).

However, it raises an interesting issue that Chipotle will need to deal with: Although Chipotle is making ethical sourcing claims, not better health claims, Americans generally assume they mean the same thing — that no GMOs, antibiotics or hormones means the food is healthier and they can eat it guilt-free without worrying about pesky things such as calories.

The campaign continues to lob new challenges at Chipotle. The most recent ad claims Chipotle’s tofu contains more hormones than meat from animals given hormones.

And other than the initial response we mentioned above, Chipotle has been silent. We think that’s the right approach — Chipotle doesn’t need to go on the defense because a bully decided to pick on it. However, Chipotle does need to go on the offense and address the very real perception that I can eat one of its burritos for lunch, believing I’m making a healthy choice, when in reality I’ve just consumed my entire recommended caloric intake for the day.

Chipotle does post calories on its website and actually lets you see, as you’re building your burrito, for instance, how many calories you’re adding per item selected. But it can and should go further by offering smaller portion options or predetermined/prepackaged lower calorie options — and then it should boldly feature these options in its ad campaign in the same way it talks about sustainable farming and the lack of antibiotics and hormones.

It’s all part of defending its brand value proposition as it’s understood in the eyes of the actual brand owners — consumers.