I've always been an eggs and avocado [1] enthusiast when it comes to breakfast, but recently, a smoothie's combination of being refreshing and ready in one minute has helped me make the transition from the stove to the blender. I've been playing around with a number of ingredient combinations, but regardless of what I toss into the mix, there's one nutrient-dense item that remains: spinach.

This leafy green might turn everything a grassy hue, but you should not be afraid to drink up. Here's why I always toss (at least) one cup of spinach into my breakfast smoothie.

It helps tone muscle: Popeye had the right idea! While your spinach-filled smoothie won't make you muscles grow immediately, a Swedish animal study found found that nitrate, found naturally in spinach, may improve muscle tone and endurance [2] in humans.

It restores your energy: Iron helps transport oxygen around the body, and people with an iron deficiency often feel fatigued and groggy without realizing it's the problem. Bumping up your iron intake can make a huge difference in how you feel, and spinach is one of the best natural plant sources [3] out there.

You can't taste it: While kale can leave your smoothie looking and tasting very green, spinach easily sneaks in without affecting flavor. If you're not convinced, try this pear, grape, and spinach smoothie [4] or this chocolate-banana blend [5]. These recipes will help you turn into a spinach smoothie convert, too.