Core answer: eGFR (CKD-EPI 2021, race-free) below 60 for three months defines CKD stage 3; serum creatinine μmol/L÷88.4=mg/dL; FFMI (fat-free mass index) caps around 25 for natural lifters; ABO type comes from parental genotype combos — O×O yields only O; 16/8 fasting exhausts glycogen near hour 12 and shifts metabolism to fat.
eGFR and CKD staging
CKD-EPI 2021 uses creatinine, age and sex:
| Stage | eGFR | Meaning |
|---|---|---|
| G1 | ≥90 | normal (needs damage evidence for CKD) |
| G2 | 60-89 | mildly reduced |
| G3a | 45-59 | mild-moderate |
| G3b | 30-44 | moderate-severe |
| G4 | 15-29 | severe |
| G5 | <15 | kidney failure |
A single low reading is not a verdict — hard workouts, meat feasts and dehydration all bump creatinine transiently.
Creatinine unit conversion
μmol/L ÷ 88.4 = mg/dL: 110 μmol/L ≈ 1.24 mg/dL. Reference ceilings ≈ 1.3mg/dL men, ~1.0 women. Cockcroft-Gault clearance = (140−age)×weight/(72×Scr)×0.85 (women) — used for drug dosing.
FFMI and body water
FFMI = lean mass kg ÷ height m² (normalized at 1.8m):
| FFMI | Level |
|---|---|
| <18 | low muscularity |
| 20-22 | well trained |
| 23-25 | near natural limit |
| >25 | likely enhanced |
Body water: Watson formulas — ~60% of weight for men, 50% women; two-thirds sits inside cells. Minimum daily intake ≈ 2.1L including food water.
Blood-type inheritance
Genotypes decide phenotypes:
| Parents | Children possible | Impossible |
|---|---|---|
| O×O | O | A/B/AB |
| A×A | A, O | B/AB |
| A×B | A, B, AB, O | — |
| AB×O | A, B | O/AB |
Two Rh-negative parents always have Rh-negative children; two Rh-positive carriers (Rr×Rr) have a 25% chance of a negative child.
Example: creatinine 110 — worry?
35-year-old man, 110μmol/L (1.24mg/dL): CKD-EPI gives eGFR ≈ 88 — G2, and without proteinuria/hematuria this is usually normal variation (muscular people run higher baselines). Next step: 3 meat-free, workout-free days, then retest; if still high, add cystatin C.
Example: running 16/8 fasting
Plan: last bite 8pm, first bite next noon (16h fast), two meals plus a snack inside 12:00-20:00. Milestones: glycogen fades ~12h → fat share climbs at 16h → autophagy strengthens at 18-24h. The eating window still needs a calorie budget and 1.2-1.6g/kg protein — fasting is not an all-you-can-eat license.
Common pitfalls
- “Normal creatinine means healthy kidneys”: creatinine can stay normal until ~50% function is lost — eGFR plus urine microalbumin is the early-screening pair.
- “Blood type proves paternity”: it can only exclude (O×O cannot make AB) — confirmation needs DNA.
- “Longer fasting is always better”: past 24h muscle breakdown accelerates and hormonal disruption risk rises — 16/8 to 18/6 is the sustainable sweet spot for most.
- “FFMI over 25 proves doping”: 25 is Kouri’s statistical ceiling; rare genetic outliers approach 26 — it is a screening heuristic, not a verdict.