Exogenous Ketones: Mimicking Starvation While You Are Well Fed
Ketones are not just a by-product of fasting - they are signalling molecules and an efficient fuel that the body can be given directly by mouth. Dr Eric Plaisance explains how exogenous ketone esters and salts raise blood ketones within 10-15 minutes, what his lab sees in liver, brain and inflammation research, and where the human evidence still has large gaps.
Overview
Dr Eric Plaisance, professor of nutritional sciences at the University of Alabama at Birmingham, has spent a decade studying how exogenous ketone esters affect metabolism, liver health and body composition. In this conversation he sets out why ketones mattered for human survival long before anyone thought of a ketogenic diet, and why taking them by mouth is a different proposition from producing them through fasting. He describes ketones as glucose-sparing fuel that the brain and heart use with unusual efficiency, and as signalling molecules that engage nutrient-sensing and inflammatory pathways, most notably the NLRP3 inflammasome.
His lab's strongest evidence sits in fatty liver disease, where multiple ketone precursors reduced liver fat, inflammation and fibrosis in animal models - in some comparisons more effectively than a ketogenic diet itself. He also walks through early work in breast cancer models, concussion and mild traumatic brain injury, heart failure and cystic fibrosis, where a seven-day low dose produced a marked drop in sputum inflammatory markers.
On the practical side he compares MCTs, ketone salts and ketone esters, explains the sodium load and gastrointestinal issues that come with salts, and covers the kinetics: a dose-dependent rise within 10-15 minutes and elevated levels for four to six hours. He is candid about the limits - no long-term human weight-loss trials, no tracer studies to define an effective dose, and sport performance as the one area where the marketing has run ahead of the data. Throughout he frames the appeal as hormetic: high circulating ketones in a fed state mimic a starvation signal the body would otherwise never encounter.
Key quotes
5The fun part of this is we're mimicking a starvation environment when we're not starving.
Ketones are for the most part going to be preferentially used by the brain and in many ways sparing glucose.
Ketones can replace about 60 to 70% of the glucose that we need as a fuel within the brain.
At 6 to 7 millimolar, it's not problematic at all.
I really want it to work, but the data is just not there at this point to support it.
Key ideas
9Ketones are a survival system, not a diet trend
Long before ketogenic diets, ketones let humans go weeks without food by converting stored fat into brain-usable fuel. That evolutionary role is the reason they engage such deep metabolic machinery.
Glucose sparing protects muscle
When ketones are available the brain uses them preferentially, so less glucose has to be made from amino acids. That spares skeletal muscle - historically the difference between surviving a food shortage and being too weak to find food.
Two doors to the same room
A ketogenic diet lowers insulin gradually over weeks; an oral ketone dose briefly raises insulin yet still drops circulating glucose. Both routes appear to improve glucose handling, but the mechanism is not yet mapped.
The ability to make ketones declines with age
HMGCS2, a rate-limiting enzyme in ketogenesis, shows falling activity and expression with age and with metabolic dysfunction. Endogenous ketone production drops accordingly - which is part of the argument for supplying them from outside.
You are always making some ketones
Even on a high-carbohydrate diet, micromolar levels circulate constantly. After a meal, ketone production is one way the liver offloads carbon from newly made fat so peripheral tissues can oxidise it.
The inflammation story runs through NLRP3
Ketones broadly dampen inflammatory pathways, the NLRP3 inflammasome above all. Plaisance sees this as the single most transferable effect across conditions - from viral illness to skin conditions like psoriasis and eczema.
Fatty liver is where the evidence is strongest
Across multiple animal models and ketone precursors, exogenous ketones lowered liver fat, inflammation and fibrosis - in some comparisons outperforming a ketogenic diet. Circulating triglycerides fell in parallel, with no change seen in cholesterol fractions.
A fuel workaround for the brain
In Alzheimer's and in the days after a mild traumatic brain injury, the brain shows glucose hypometabolism. Ketone uptake appears to stay intact, so ketones can supply energy where glucose no longer can - a rationale that still needs proper trials.
MCTs, salts and esters behave differently
MCTs give a slower, sustained rise via the liver; salts and esters raise ketones fast. Newer conjugates such as bis-octanoyl butanediol combine a rapid spike with a sustained release lasting around four hours.
Practical takeaways
6- 1
Expect a fast rise and a four-to-six-hour window 1:03:00
Oral ketone salts and esters raise blood ketones within 10-15 minutes, typically to 0.5-3 mmol/L depending on dose, with elevated levels sustained for four to six hours.
- 2
Salts carry a sodium load 58:00
Many ketone salt products deliver 500-1,000 mg of sodium per dose, and salts are where most of the mild, transient nausea shows up. Esters were developed partly to avoid that load.
- 3
Check whether the form is D or racemic 59:00
D-beta-hydroxybutyrate is the biologically active form, yet many salts are a 50/50 D/L blend. The L form converts slowly, which muddies comparisons between products.
- 4
Start low, then build up 1:09:00
Research doses run from around 12 to 25 grams of a ketone ester, typically two to three times a day spread out. Plaisance's own habit is a morning dose and one in mid-afternoon.
- 5
Timing around meals changes the response 1:10:00
With some esters, taking a dose alongside a high-carbohydrate meal can cut the measured blood ketone response by up to half. Whether that matters is unknown, but a lower-food window gives a higher reading.
- 6
Home measurement is limited to BHB 1:06:00
Finger-stick meters read beta-hydroxybutyrate only. Acetoacetate can be estimated semi-quantitatively with urine strips or via breath devices that detect acetone.
Topics & chapters
15Cold open: starvation signalling while well fed
Plaisance frames the appeal of exogenous ketones as hormetic mimicry - high circulating ketones in a fed state, something humans essentially never experience naturally.
Why ketones matter to humans at all
Why ketones underpinned human survival through food scarcity, and why that makes them interesting to people who are neither fasting nor on a ketogenic diet.
Ketones versus fatty acids as fuel
Which tissues burn what, and why fatty acid oxidation in muscle and kidney appears designed to reserve ketones for the brain.
Do oral ketones mimic a ketogenic diet?
The insulin and glucose responses differ from a ketogenic diet, yet both routes improve glucose metabolism. Human weight-loss data remains missing.
Ketone production and ageing
HMGCS2 activity falls with age and metabolic dysfunction, so the body's own ketone output declines - a finding still being debated.
Ketones after a meal
Micromolar ketone levels circulate constantly, and post-meal ketogenesis helps the liver shuttle carbon out to peripheral tissues.
Inflammation, NLRP3 and the COVID window
How ketones dampen inflammatory cascades, and the trials the lab hoped to run during the pandemic but never got off the ground.
Cancer models, concussion and heart failure
Early animal work in a 4T1 breast cancer model, preliminary human concussion studies, and the case for ketones as an efficient fuel in heart failure.
Fatty liver disease and blood lipids
Reductions in liver fat, inflammation and fibrosis across models, increased fatty acid oxidation, and falling circulating triglycerides with no change in cholesterol fractions.
Alzheimer's and the brain's fuel problem
Impaired glucose uptake in the ageing brain, why ketones can substitute for 60-70% of that fuel need, and the parallel with mild traumatic brain injury.
Why ketone research lagged
The lasting confusion between nutritional ketosis and diabetic ketoacidosis, funding difficulties, and the 2012 arrival of the ketone monoester.
MCTs, ketone salts and ketone esters
How each raises ketones, why medium-chain fats give a sustained rise, and what butanediol conjugates add to the picture.
Tolerability, sodium and the D/L question
Mild transient nausea, the sodium load in salt products, and why racemic D/L blends make the research harder to interpret.
Kinetics and home measurement
The 10-15 minute rise, four-to-six-hour duration, and the practical options for measuring BHB, acetoacetate and breath acetone.
Doses, personal routine and honest caution
12-25 grams two to three times daily, his own morning-coffee habit, and a clear warning that exercise performance claims are not supported by the data.