Creatinine is the primary metabolic byproduct of creatine breakdown in the body. Each day, about 1-2% of creatine stores in the body are degraded into creatinine. Many of the liquid creatine supplements sold today are also largely composed of creatinine, since creatine is unstable in liquid form. Although creatinine is relatively harmless, it does not provide any of the ergogenic benefits associated with creatine. It is therefore more of a creatine waste product than anything else.
A common test of kidney function is involves testing for the level of creatinine in the urine. When creatine is broken down into creatinine, it is excreted from the body via the kidneys. Normally, the level of creatinine found in urine samples remains in a constant range. If it rises above that range, it suggests that the filtering capacity of the kidneys has been compromised. This, in turn, would point to the onset of possible renal failure. Under normal conditions, the urinary creatinine level doesn't rise until there already has been extensive damage to the kidneys. But there are some notable exceptions to this rule.
One such exception is whether you are consuming a creatine supplement. The body produces an average of one gram of creatine daily, produced in the liver, kidneys, and pancreas. If you eat foods naturally rich in creatine, such as red meat, you ingest about another gram of creatine. In contrast, just one teaspoon of the most common creatine food supplement, creatine monohydrate, supplies five grams of creatine, or about the same amount found in 2 1/2 pounds of beef. If you opt for a creatine loading technique, such as ingesting 5-6 teaspoons of creatine for 5-6 days, after two days, half the creatine you ingest will be rapidly converted into creatinine. If you were to have a urinary kidney test for creatine during that time, you would show elevated levels of creatinine, this making your doctor think you were in the early stages of kidney failure.
Another way that the urinary creatinine test can be skewed is by eating red meat prior to the test. This was shown in a new study involving 80 subjects. The group consisted of healthy volunteers and diabetic patients with various stages of chronic kidney disease. The subjects were provided with either cooked meat meal or a non-meat meal on different days. The meals supplied 54 grams of protein, and the subjects also consumed 250 milliliters of water.
The results showed that the cooked meat meal led to a significantly increased serum creatinine level, along with a fall in the glomerular filtration rate (GFR), another measure of kidney function. The elevated creatinine level shown in the subjects subsided after 12 hours of fasting.
The study authors suggest that a large percentage of creatine found in meat is degraded into creatinine when the meat is cooked. The resulting excess creatinine is rapidly excreted, and can show up in a medical test for creatinine levels. The solution to this problem is to measure creatinine under fasting conditions, along with a test for GFR, which would product a more accurate picture of actual kidney function. Another method involves looking at the blood urinary nitrogen (BUN) level compared to the creatinine level.
The message derived from this study is that 1) Cooked meat may not contain as much creatine as supposed; 2) Don't have any creatinine tests, blood or urinary, within 12 hours of consuming a meat meal or ingesting a creatine supplement.
Reference
Nair, S, et al. Effect of a cooked meal on serum creatinine and estimated glomerular filtration rate in diabetes related disease. Diabetes Care 2013; In press.
©,2013 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited.
