"Collagen is one of the most abundant proteins in the body. It gives our skin strength and elasticity and replaces dead cells. It's critical for hair, nails, and digestion and basically glues our joints and tendons together. Unfortunately, production slows down in your 20s, so it's important to supplement. We put powder in our smoothies or coffee daily! Collagen latte, anyone?" — Elizabeth and Dale, @sweatsandthecity