Creatine is one of the best-selling supplements of all time, particularly to athletes. It is marketed as an energy booster, and a way to increase endurance. Here’s how it works.
This one is a three part biochemistry interlude. (Brace yourself.)
Part 1: What Creatine Is
Creatine is a peptide, or a short string of amino acids. Longer strings of amino acids make proteins; short strains make peptides. This one is built from glycine, arginine, and methionine. Therefore, your body can manufacture it from the protein you eat (or you can also ingest it ready-made in meat and fish). Once this happens, the body attaches a phosphate molecule to it, to make phosphocreatine in the muscles.
Part 2: How Creatine Donates Energy
Your body’s major energy currency is ATP, Adenosine Tri-Phosphate. It releases energy by releasing one of those phosphate molecules, turning it into ADP (Adenosine Di-Phosphate). ATP is a very biochemically expensive molecule, though—so the quickest way to get more ATP is to just regenerate the ADP that’s already hanging around. Phosphocreatine can do this by donating its extra phosphate.
Part 3: Creatine and Creatinine
When your body is trying to get rid of creatine, it becomes creatinine, which is toxic and has to be excreted. The kidneys do the job—and this is why you’ve probably seen creatinine on metabolic panels ordered by your doctor. Creatinine is a marker of kidney function: if the kidneys are efficient, levels will stay low. If levels are high, that means there’s a bottleneck at the kidneys. They’re backed up.
If you’re supplementing with creatine, there might be a backup just because there’s a higher circulating level of creatine in your body than in the average person’s. The kidneys are working just fine, there’s just more creatinine for them to deal with. You might also end up with high creatinine if you eat a very high protein diet, for the same reason: there’s more circulating creatine to begin with, and therefore more for the kidneys to eliminate.
Physiology Interlude: Kidney Function and Protein
This is a good time to discuss a common topic that comes up here: is high protein intake (or creatine supplementation) therefore bad for the kidneys?
According to this study, the answer is, only if you have reduced kidney function for some other reason. If you do, then you certainly will need to watch your protein intake, as you don’t want to overwork organs that are already having trouble. But if your kidney function is fine, there doesn’t appear to be a significant reason to be concerned.
Creatine does seem to be helpful for high intensity exercise particularly. It can also help with energy and even concentration.
If you supplement with creatine or eat a high protein diet but do not otherwise have reduced kidney function, a higher level of creatinine on a metabolic panel is unlikely to be concerning.