Staying hydrated is a must to keep your energy sky-high. “Even if you're slightly dehydrated, you feel some fatigue,” says Samantha Heller, R.D., an exercise physiologist and the Clinical Nutrition Coordinator at Griffin Hospital. “The body is around 80 percent water; all biochemical reactions happen in water. If you're not getting enough water, the body doesn't produce the energy it needs to function properly.” The Institute of Medicine advises that men consume roughly 3 liters (about 13 cups) of total beverages daily, while women should get 2.2 liters (about 9 cups). So be sure to drink water throughout the day. Tea, soup and seltzer are also options.