The organic health halo is so strong that consumers on average believe an organic cookie has 40% fewer calories than a “conventional” one. They also believe that organic snacks have more fiber and other health benefits than traditional ones. These misperceptions are leading Americans to unknowingly overeat, according to an intriguing new study from Cornell University.

Cornell’s Food & Brand Lab found similar results when they studied foods labeled “healthy” and “low fat.” When eating at restaurants that advertise healthy offerings, consumers assume all the options are significantly lower in calories, and give themselves permission to eat more. Similarly, the average consumer believes that the appropriate serving size for a low fat food is 25% greater than for its “regular” counterpart, and often reward themselves for their smart choice by over indulging.

The people most likely to fall into the “It’s organic so it must be lower in calories” trap are those who buy the most organic food and those who usually read nutrition labels. They are not the people I would have thought most prone to leaping to the wrong conclusions. And that brings us back full circle to the fact that assumptions can be misleading.