What are the impacts on learning of allowing students to eat in class? My school has a recommendation, but not a requirement, not to let students eat during class. I am wondering if I should make this a rule or not for the classes I teach. I am concerned about my undergraduate students.

On one hand, the noise from rustling bags and crunching chips and bottles falling on the floor can be distracting. On the other hand, hungry students are distracted by hunger. This is a particular problem for my classes which start before 8 AM as students often skip breakfast and want to eat it during class (because they do not want to wake up early enough to eat before coming to school).

Since my main concern is on the learning, I would like to know how the issue of allowing eating during class actually impacts student learning.
Most of the answers here suggest limiting or prohibiting eating in the classroom, but I have to disagree.  

First, students generally do not control their own schedules.  Personally, I often had five or six hours of class back-to-back as an undergrad, and I was not unusual in that regard.  Yes, there are breaks between classes, but students need that time to get to the next classroom.  In addition, many professors let their class go overtime, reducing the length of the break.  If you prohibit eating, hungry students will simply choose to arrive late after getting a snack, which defeats the idea of minimizing disruptions by prohibiting eating.

Second, you don't know what medical issues a particular student has: they may be diabetic or need to eat at regular intervals for other reasons.  While a student can tell you about this at the start of the term, I don't like the idea of forcing students to discuss their medical issues with every professor, every term.  After all, students who get special classroon accommodations due to a disability are not obliged to tell their professors what the specific disability is.

For these reasons, if the university does not have a specific policy, I would tend to be lenient at first.  Most students are reasonable people who won't show up to class with a five course dinner.  If a specific concern arises during the term, such as very noisy food or garbage being left behind, you can address it either with the individual student or the class as a whole, as appropriate.