Spirulina is a powdered, high-protein seaweed supplement. The dried stuff is about 60 percent protein, and, like quinoa, it’s a complete protein, meaning it can be converted directly into muscle in the body and is thus a great weight loss tool. A tablespoon of the blue-green algae delivers 8 grams of metabolism-boosting protein for just 43 calories, plus half a day’s allotment of vitamin B12, which in and of itself can give you more energy and boost your metabolism. Try tossing some spirulina into a smoothie and watching the pounds melt off. For more skinny smoothie ideas, check out this list of smoothie recipes for weight loss!