How Many Calories Are in One Bag of Microwave Popcorn?

When popcorn is made without oil or butter and eaten in moderation, it's a healthy, fiber-rich snack. However, eating a whole bag of microwave popcorn — particularly if it's flavored with butter — won't do your health any good.

The number of calories in a bag varies among microwave popcorn brands and depends on what's been added to the bag. For example, according to the USDA, a 100-gram bag of low-fat microwave popcorn has 424 calories per bag and 9.5 grams of fat, as well as 14.2 grams of fiber.

However, 100 grams of butter-flavored microwave popcorn made with palm oil has 535 calories and 30 grams of fat, but just 10 grams of fiber. The same flavor of popcorn made with partially hydrogenated oil, a dangerous trans fat, has 557 calories, 34 grams of fat and 10 grams of fiber.

If you're a big fan of popcorn as a snack, your best bet is air-popped popcorn, rather than the microwave variety. An equivalent amount, or 100 grams, of air-popped popcorn has 387 calories, 4 grams of fat and 14.5 grams of fiber. To keep the calories in check, stick to eating just one or two cups of this popcorn — each cup has just 31 calories and less than a half a gram of fat.

The calories in popcorn aren't the main concern with the snack. In 2015, the U.S. Food and Drug Administration released a final determination that partially hydrogenated oils, a type of trans fat, are not generally recognized as safe.

Trans fats are typically used to prolong the shelf life of food, but can also be used to flavor microwave popcorn — to the detriment of your health, according to the Mayo Clinic. Trans fats raise your LDL cholesterol, which is the unhealthy type of cholesterol, and decrease the good cholesterol, HDL.

Butter-flavored popcorn made with palm oil does not contain trans fats, but it shouldn't necessarily be considered healthy. Palm oil contains a significant amount of saturated fat, which should comprise less than 10 percent of your total daily calories, due to its effect on cholesterol, the Mayo Clinic notes.

Because it's a whole grain, popcorn has a good amount of fiber in it. This indigestible type of carbohydrate helps your body regulate its use of sugar, which keeps hunger in check, as well as promotes healthy digestion.

It might also reduce the risk of certain health conditions, such as heart disease, diabetes, diverticular disease and constipation, according to the Harvard T.H. Chan School of Public Health. Both children and adults need between 20 and 30 grams of fiber a day, but most only get about 15 grams a day.

Popcorn can go a long way toward helping you meet your fiber goal, given that a bag (or the equivalent amount) has anywhere between 9.5 and 14.5 grams of fiber in it, according to the USDA. When you enjoy a bag of popcorn as a snack, it can add that extra boost of fiber to your diet to ensure you're getting enough of the nutrient each day.

Microwave popcorn bags used to contain a chemical known as perfluorinated compounds (PFCs), which helped prevent the oil from the popcorn from seeping through the bag, and created "grease-proof" packaging. In the past, there was a concern over a link between microwave popcorn and cancer.

A study published in the November-December 2013 issue of ‌Environmental Health Perspectives‌ linked the use of PFCs and cancer, although the study didn't specifically look at microwave popcorn bags. In 2016, the Food and Drug Administration (FDA) banned the use of PFCs in food packaging, so microwave popcorn bags no longer use this additive.

However, the FDA noted that it removed approval for the chemical because manufacturers had voluntarily stopped using it and not because there was a safety evaluation done for the chemical. Therefore, these days, there is no need to be concerned that your favorite microwave popcorn brands could be a risk to your health when it comes to cancer.