Olympic triathlete Jarrod Shoemaker made a critical change in his fitness regimen, based on input from one of his trainers. But it didn’t come from his running, swimming, or biking coach; rather, it was from a Web program he uses to monitor key biomarkers in his blood.

The program, InsideTracker, found that Shoemaker had high levels of Vitamin D, which could lead to muscle fatigue and weight loss. So at InsideTracker’s suggestion, he cut back on eggs and milk and started eating more strawberries, corn, and celery. His vitamin D levels dropped, and Shoemaker avoided hitting a wall in his training.