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Hi SELF Family,
Your kidney function test came back a little off, so you did what a lot of people do next. You ate lighter for a week, maybe you bought the tea, and the repeat test looked better.
That better number is real. This letter is about why it probably had nothing to do with the tea, and how to make sure your next kidney test is telling you the truth.
Start with the number itself. The kidney function number on your lab report is the eGFR, short for estimated glomerular filtration rate. In plain language, it estimates how much blood your kidneys filter each minute, and it prints on your report as mL/min/1.73 m². For most adults, above 90 is normal. Below 60 for three months or more is the line doctors use for stage 3 kidney disease.
The word that matters is estimated. A routine blood test does not measure your filtration directly. The lab measures one waste product in your blood, creatinine, and a formula turns it into your eGFR. Creatinine comes from your muscles, and your kidneys clear it, so a higher level in the blood usually means the kidneys are clearing less.
Creatinine has a second source, though, and the formula cannot see it. Meat contains creatine, and cooking converts some of it into creatinine. You eat it, you absorb it, and it shows up in your blood looking exactly like the creatinine your muscles made. The formula reads the higher level as weaker kidneys.
In 2007, a team in Scotland measured how big that effect is. They fed 32 people a meal containing cooked meat and drew blood before and after. Within one to two hours, the group's median eGFR fell from 84 to 59.5. A second marker in the same blood samples, cystatin C, which does not come from muscle or meat, was generally unaffected by the meal. A meat-free meal on another day barely moved anything. That study was published in Annals of Clinical Biochemistry.
One meal moved a group across the stage 3 line in two hours, and their kidneys had not changed.
A second study, in Diabetes Care, did the same thing in 80 people, including people with diabetes who already had kidney disease. After a standardized cooked-meat meal with about 54 grams of protein, 6 of the 16 people at stage 3a came out looking like stage 3b. After 12 hours without food, the effect was gone in every participant.
Now run the same arithmetic backwards. A cleanse almost always comes with instructions: eat light, skip the meat, drink more. Follow them for a week and less creatinine enters your blood, so the eGFR rises on the retest. Nobody has run a trial of a cleanse week the way these teams ran the meat meal, but it is the same mechanism pointed the other way. The result is real, and it does not show that the tea repaired anything or flushed anything out.
Your kidneys are the thing doing the cleaning.
They filter about 180 liters of fluid out of your blood every day, roughly 47 gallons, and return almost all of it. What changed during the cleanse week was what you put in front of the test.
If you bought one because a number frightened you, that is a reasonable thing for a worried person to do. The label was misleading. You were not.
A kidney trend is only as good as the conditions it was measured under. Three things put those conditions in your hands.
First, test the same way every time. If your last blood draw was fasting, make the next one fasting too, at about the same time of day.
Second, skip cooked meat on the day of the test, or fast overnight. The 2007 authors recommended exactly that, and the 2014 study saw the effect clear after 12 hours without food. This is about the test, not a reason to avoid protein.
Third, tell your doctor what changed between the two tests, including any creatine supplement, and if a result does not fit the rest of your picture, ask whether a cystatin C test makes sense. It is the marker that did not move when the meat did.
The video goes where this letter cannot: it opens a cleanse pouch and walks through the ingredients one by one, names the herbs with documented kidney injury reports behind them, including St John's wort, aristolochic acid, and star fruit, and gives the one drink swap backed by 127,830 people in the UK Biobank. Watch The Truth About Kidney Cleanses: What Your Doctor Won't Tell You.
With gratitude,
Dr. Sean
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