When Colin O’Brady and his friend Lucas Clarke set a new pairs category record in the Race Across America last June, they were burning close to 15,000 calories a day and relying on gels and drink powders to make it up.

In an article in Muscle & Fitness, O’Brady said he relied partly on AG1, a powdered drink supplement that its maker claims was shown in a clinical trial to enrich the gut microbiome. O’Brady said he’s used the product for years during training as well as during and after the race. 

The pair aimed to complete the race in under six days as part of its Sub6 Project. While they fell short, finishing in six days, six hours and 43 minutes, they shattered the previous record by more than five hours. They raced more than 3,000 miles through 14 states.

O’Brady is no stranger to endurance records. The RAAM record was his eleventh, but perhaps his best-known was becoming the first person to trek unsupported and alone across Antarctica. The 54-day trek covered 932 miles in average temperatures of -30 degrees. The journey is chronicled in his book “The Impossible First.”