Plantains are considered a grain in Bright Line Eating. However, they are very high in natural sugar (they have even more than a yam or sweet potato). That doesn’t mean you can’t eat them—it just means you should exercise a bit of caution.
When you first start the program and only have grains for breakfast, plantains are not recommended for a breakfast grain. However, after several months doing Bright Line Eating, you can try them if you want. As always, if they trigger you, avoid them.
4 oz. of cooked plantains count as one grain serving.