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2. Spirulina

Spiru-what? Spirulina is—stay with us here—a blue-green algae that nutritionists love for its concentrated levels of nutrients including iron, copper, and protein, says Pamela Nisevich Bede, MS, RD, sports dietitian with Abbott. A single one-tablespoon serving contains only 20 calories—and about 80 percent of those calories come from protein, making it a good choice for those looking to maintain both muscle and metabolic health. Plus, since it contains all nine of the essential amino acids, which is rare among plant-based proteins, spirulina can be helpful to anyone reducing or eliminating their intake of meat, eggs, or dairy. 

Try it in:

• Brain-Boosting Smoothie