Popcorn can be a healthy snack depending upon how it's prepared.
Some people have written me asking if making popcorn with extra virgin olive oil is a good technique. Unfortunately, I don't think it's good to prepare popcorn with oil, even healthy oils, since I strongly believe in avoiding the heating of vegetable oils, including olive oil. Heating olive oil can cause it to oxidize and damages its delicate polyphenol antioxidants.
A more nourishing way to prepare this same snack would be to air-pop the popcorn in an air popper and then to add extra virgin olive oil and, if you want, a little sea salt after the popcorn was popped. How many calories you end up with depends on how much olive oil you use. One cup of air popped popcorn, for example, contains only 30 calories or so. Olive oil contains about 250 calories per ounce (2 tablespoons). Still, even with two tablespoons' worth of olive oil, most people would have little trouble fitting this type of healthy snack into their Healthiest Way of Eating.
As for microwave popcorn, I have my concerns. I don't think that microwaving of popcorn presents a risk-free alternative. That's because there has been some evidence that the Teflon-like coating of some bags used for microwave popcorn can get broken down with heat into unwanted substances, including perfluorooctanoic acid (PFOA). The chemical, which appears to be potentially carcinogenic in lab animals, is partially released onto the popcorn when the bag is heated up and can then be absorbed, once again in partial amounts, into the blood stream. The U.S. Food and Drug Administration (FDA) is currently studying the effects of this chemical in more detail. Additionally, the U.S. Environmental Protection Agency (EPA) is studying potential problems associated with the artificial butter flavoring used in microwave popcorn.
When purchasing the popcorn itself, I'd encourage you to consider organic popping corn. It's often not much higher in price than non-organic popping corn, and the potential health benefits here are important. Organic popping corn will not have the pesticide residues or other toxic residues commonly found on conventionally grown corn, and it will not have been genetically engineered (as genetic engineering is not allowed in production of certified organic foods).