How do the metabolites xanthine and total indoxyl sulfate help us to understand if an individual is overtraining?


When an athlete’s xanthine is elevated, it is usually due to regular or excessive cardio-based training like long-distance running or biking. This happens because the body’s energy system is pushed to keep up with the increased needs of these types of exercises. Athletes want to avoid elevated xanthine because it can be converted into uric acid, which can lead to inflammation and slowed recovery. Elevated xanthine and uric acid can also form crystals in kidneys and muscles. 

Total Indoxyl Sulfate

Indoxyl sulfate is a uremic toxin that the kidneys remove from the body. When it’s at normal levels, it acts as an antioxidant; at high levels, indoxyl sulfate can indicate gut dysbiosis, excessive protein intake (or amino acid supplementation), fad dieting, or dehydration. We have frequently seen it elevated in athletes who focus on weight training. This could be due to any of the factors previously mentioned. The mechanism has not yet been studied enough to provide a definitive cause.

If an athlete can't or won't slow or reduce training, they should be aware of the elevated metabolites and focus on antioxidant (such as vitamin C) intake to assist with xanthine's conversion to uric acid. Hydration is also key because uric acid and indoxyl sulfate are uremic toxins that must be flushed from the body. It is important to understand how each supplement affects the body. It’s also a good idea to re-evaluate supplements and determine if they are truly needed. The best way to do this is to retest every 3 months.