Before your blood test
How do keto, carnivore and high-protein diets affect blood test results?
Short answer
Very-low-carb and high-protein diets change several markers predictably: LDL cholesterol often rises (sometimes dramatically in lean people), triglycerides fall and HDL rises, BUN climbs with protein intake, uric acid rises in the first weeks, sodium and potassium can dip during the transition, and ketones appear in urine. Creatinine may be slightly higher with heavy meat intake and more muscle. Fasting glucose and A1c usually improve. Tell the clinician about the diet so the lipid result is read in context.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
Which results does it affect?
| Marker | Direction | How long | What to do |
|---|---|---|---|
| LDL cholesterol, ApoB | can raise | Weeks into the diet; persists while on it — largest in lean, active people | Recheck with ApoB; discuss cardiovascular risk rather than dismissing the rise as 'diet noise' [source] |
| Triglycerides | lowers | Within weeks | None needed — expected improvement [source] |
| HDL cholesterol | raises | Weeks to months | None needed [source] |
| BUN | raises | While protein intake is high | A high BUN with normal creatinine and eGFR reflects protein intake, not kidney damage [source] |
| Uric acid | raises | First 4–8 weeks, then often settles | Relevant if you have gout or a history of kidney stones [source] |
| Creatinine | can raise | Hours after a large meat meal; chronically with more muscle | Fast before the draw; cystatin C is an alternative kidney marker unaffected by meat [source] |
| Sodium, potassium, magnesium | can lower | First weeks ("keto flu") | Hydrate and mention the diet if a metabolic panel is drawn in the transition [source] |
| Fasting glucose, insulin, A1c | lowers | Weeks to months | None needed — expected improvement [source] |
Why does LDL rise on a ketogenic diet?
Most people on a ketogenic diet see triglycerides fall and HDL rise, which is favorable. A subset — often lean, athletic people, sometimes described as 'lean mass hyper-responders' — see LDL and ApoB rise sharply, occasionally above 200 mg/dL. Whether that rise carries the usual cardiovascular risk is actively studied; current guidelines treat elevated ApoB as a risk factor regardless of the cause. The right response is a conversation with a clinician armed with ApoB and, if warranted, Lp(a) and a coronary calcium score — not ignoring the number and not panicking over it.
A high-carb refeed for a few days before the draw can lower LDL temporarily and hide the effect; testing while eating your actual diet gives the honest picture.
Why do BUN and creatinine rise on a high-protein diet?
BUN rises because urea is the by-product of protein metabolism; on its own, with a normal creatinine and eGFR, it says nothing about kidney health. Creatinine can be nudged up by a large meat meal within hours (cooked meat contains creatinine) and by greater muscle mass, so a fasting draw and a cystatin C are the fair comparison if the eGFR reads lower than expected.
Common questions
Should I eat carbs before a cholesterol test on keto?
No — that produces a result that reflects neither your diet nor your baseline. Test on your usual diet and tell the clinician. If LDL or ApoB is high, that's real information to discuss.
Does a high-protein diet damage kidneys?
Not in people with healthy kidneys, based on current evidence. It raises BUN, which is expected. If you already have kidney disease, protein intake is something to set with your clinician.
Why is my uric acid high on keto?
Ketones compete with uric acid for excretion in the kidney, so levels rise in the first weeks and often settle. If you have gout, that window can trigger a flare — worth planning for.
Educational content, not a diagnosis. Lab results are one input; a clinician interprets them with your history and exam.