Hi SELF Family,

Tomorrow night I go live for members to answer the questions you asked most this month. Since the end of August I read through roughly 700 comment threads, grouped the questions by how many different people asked them, and kept the five I could answer with named studies and the current kidney guideline.

A lot of those questions came from the same worry: a number on a lab report moved, and nobody told you why. If that has kept you up at night, it was a reasonable reaction. Tomorrow is about explaining it.

Here's what's on the list.

1. Does the kind of coffee matter?

More of you asked about coffee than anything else: decaf, instant, milk, tea, and whether the benefit comes from the coffee or from the kind of person who drinks it. That last question is the right one to ask, and there's a study built to answer it. Researchers in the United Kingdom compared people by the coffee-drinking genes they were born with, rather than by the coffee they said they drank. Each extra cup a day was linked to 16 percent lower odds of stage 3 kidney disease or worse, a finding published in the American Journal of Kidney Diseases. I'll explain why that design is more convincing than the usual coffee headline, and the one place where the type of coffee clearly matters.

2. My urine is foamy, but my labs are normal

Your eGFR, the filtering number from a blood test, and a urine albumin test answer two different questions. Protein can leak into the urine while the filtering number looks completely normal. I'll cover which test to ask for, how to collect it, and how often foam actually turns out to be protein.

3. Is creatine hurting my kidneys, or just my kidney test?

Creatine raises creatinine, the blood marker most eGFR results are calculated from, so the number on your report can drop even when your kidneys are filtering just as well as before. A review of 26 randomized studies, published in July in International Urology and Nephrology, tested that directly by measuring filtering a second way. I'll show you what it found, and who still hasn't been studied.

4. My eGFR moved. Should I worry?

The 2024 international kidney guideline uses a specific line to separate a real change from ordinary test-to-test noise, and I'll work through it with real numbers. I'll also show you what one cooked-meat meal did in a 2007 study in the Annals of Clinical Biochemistry: the typical participant's eGFR fell from 84 to about 60 within one to two hours. That's a normal filtering number sliding to the edge of stage 3 from a single meal.

Much of what worried you this month was a number moving for a reason other than kidney damage.

5. Did a medicine hurt my kidneys?

One of the drugs you fear most in the comments is one the kidney guideline recommends.

And one that barely came up as a worry sits in many medicine cabinets. I'll sort the common ones into four groups, including where amlodipine fits, so you know which questions to bring to your own doctor.

Between the questions, I'll take a few minutes on a new diet trial published on August 27 in Cell Metabolism, which compared ketogenic, Mediterranean, and plant-forward eating at the same amount of weight loss. I'll tell you what it found, and what it doesn't tell someone with kidney disease. We'll finish with the three numbers I'd want you to bring to your next appointment.

The members live is the center of SELF Supporter membership. Once a month, on the fourth Thursday at 6 PM Pacific, members spend about an hour with me and I answer their questions on camera. Join today and you can watch tomorrow and bring your own question to the chat. Members also get every new video 48 hours before everyone else, plus members-only posts.

Join to watch tomorrow

Already a member? It streams on the channel at 6 PM Pacific, and the replay stays up afterward if you can't make it live.

With gratitude,

Dr. Sean

From SELF Principle

The research behind this letter

1. Kennedy OJ, Pirastu N, Poole R, et al. Coffee consumption and kidney function: a Mendelian randomization study. American Journal of Kidney Diseases. 2020;75(5):753-761.

2. de Souza Almeida A, da Silva LOD, Takahasi BNA, et al. Impact of creatine supplementation on kidney health: a systematic review and meta-analysis. International Urology and Nephrology. Published online July 27, 2026.

3. Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International. 2024;105(4S):S117-S314.

4. Preiss DJ, Godber IM, Lamb EJ, Dalton RN, Gunn IR. The influence of a cooked-meat meal on estimated glomerular filtration rate. Annals of Clinical Biochemistry. 2007;44(Pt 1):35-42.

5. Petersen MC, Smith GI, Farabi SS, et al. Effect of diet macronutrient content on the cardiometabolic response to weight loss: a randomized clinical trial. Cell Metabolism. Published online August 27, 2026.

This content is for educational purposes only and is not medical advice. Always consult your healthcare provider for individual care. The views expressed are Dr. Hashmi's own and do not represent his employer.

Never start, stop, or change the dose of any prescription medication without consulting your physician.