Eating enough — and getting the right nutrients — is crucial to feeling and performing your best, especially if you exercise regularly.bymuratdeniz/Getty ImagesToo many health-conscious people aren't eating enough to support their exercise, a dietitian said.Undereating can lead to fatigue, trouble sleeping, higher chance of injury, and health risks.Don't be afraid to try eating more for a few weeks to see how you feel, even if you want to lose weight.A common diet mistake could be stalling your workout gains and interrupting your energy outside the gym, according to a dietitian.Brittany Werner, a registered dietitian nutritionist (RDN) and director at nutrition coaching company Working Against Gravity, said she frequently sees ambitious, health-conscious people who are under-eating.