It can be difficult to find snacks that fit into the Atkins diet, because most common snacks are high in carbohydrates. Whether you'll be able to eat popcorn on the Atkins diet depends on which version of the diet you choose and which phase you're in. Even when it's allowed, it may be difficult to fit it in within your recommended carbohydrate limit before you reach the maintenance phase.
A cup of popcorn provides about 5 grams of net carbs, or carbohydrates minus fiber. To eat popcorn on the Atkins diet, you need to factor in its carb content.
If you're following the Atkins 20 diet plan, you can only have 20 grams of net carbs per day, which you're supposed to get mainly from green leafy vegetables and other nonstarchy vegetables, which excludes popcorn. You can't have popcorn and other whole grains until the third phase of this version of the Atkins diet.
The Atkins 40 diet plan allows twice the carbohydrates and also lets you consume whole grains like popcorn as well as nuts and fruits for up to two-thirds of those carbohydrates, with the remaining one-third coming from vegetables. As you get closer to your weight-loss goal, you increase your carbohydrate intake, making it easier to fit in a serving of popcorn.
If you can fit popcorn into your diet, you'll need to practice portion control. The average serving of popcorn is larger than 1 cup, so make sure you measure your snack.
The Atkins diet recommends foods that are low on the glycemic index, meaning they don't cause large increases in blood sugar after you eat them. Foods with a low glycemic index have a score of 55 or below, so popcorn just makes it into this category with an average GI of 55.