The Deconditioning Tax: Why One Workout Cost Me Three Days of Ketones

Why one workout cost me three days of ketones — and why that is a tax, not a failure

Saturday, September 5, I ran for an hour.

I want to be precise about that, because I am a physician and precision is the job. I ran for one hour without stopping. Then I walked for another fifty minutes. Five miles in all. I am sixty years old, and the last time I ran was before the pandemic.

My knees did not hurt. That story is in the companion piece. This one is about what my ketone meter did afterward, because it did something I did not expect, and it did it twice.

The morning of the run, 3.7. Right after, 3.3. The next morning, 3.1. That evening, 2.6. The morning after that, 3.6 and climbing. Three days below my floor of 4.0 from one workout.

I have measured my ketones every day for four years. I know my own pattern. Normally a workout dips the number for an hour or two and it recovers by the afternoon. Three days is new. And it happened twice — once after a hard workout on August 27, and again after Saturday's run. Same shape both times.

Most people would call that a failure. I am going to show you it was a tax. Taxes are predictable. Failures are not. If you can predict it, you can stop being afraid of it.

The words I'll use

You should not have to stop and look anything up. So here is everything, in plain words, before I use it.

Ketones. A fuel your liver makes from fat when carbohydrate is scarce. Your brain and heart can run on it. So can your joints, as we will see. The one I measure is called beta-hydroxybutyrate — say "BHB" — a small molecule your liver assembles out of fat and ships into the blood. I will just say the ketone number, or the meter.

The meter. A finger-prick device. It reads blood BHB in millimoles per liter. You do not need the unit. Above 0.5 you are in ketosis. My floor is 4.0. My cruising range is above 5.

Glycogen. Sugar packed into storage. Your muscles keep a pantry of it. Your liver keeps a smaller pantry. When you exercise hard, you eat from the pantry.

Glucose. Blood sugar. The liver can make it from scratch when it has to. That making-from-scratch is called gluconeogenesis — say "GNG" — and it matters here, so I will explain it when we get there.

Insulin. The hormone that tells your body to store fuel rather than burn it. When insulin is up, ketone production goes down. That is the master switch.

Cortisol. The stress hormone. Your adrenal glands release it when your body decides it is under threat — from a hard workout, from dehydration, from standing up too fast when your blood pressure drops. Cortisol tells the liver to make more glucose. We will come back to this.

Deconditioning. The medical word for what happens to a body that has not been asked to do much for a long time. Not injury. Not disease. Just a body that has stopped expecting to work.

PGC-1α. Say "PGC-one-alpha." A protein that acts as the master foreman for building new mitochondria. When it is switched on, your cells build more power plants. Exercise switches it on. So does BHB, through a different door. We will come back to this.

HDAC. Histone deacetylase. Say "aitch-dee-ay-cee." A family of enzymes that act like librarians in your cell's nucleus, deciding which genes are open for reading and which are shelved. HDACs shelf genes. BHB blocks HDACs, which unshelves genes — including the ones that protect against oxidative stress.

HCAR2. Hydroxycarboxylic acid receptor 2. Say "aitch-car-two." A receptor — a docking station — on the surface of cells that BHB plugs into. When BHB docks, it sends an anti-inflammatory signal into the cell. Think of it as a keyhole that BHB fits, and when the key turns, the cell calms down.

Delayed onset muscle soreness. Say "DOMS." The stiffness that arrives a day or two after a hard workout and peaks around day two or three. Caused by small tears in the muscle and the repair response, not by lactic acid. I will just call it the soreness.

Mitochondria. The power plants inside your cells. They burn fuel to make ATP — adenosine triphosphate, the cell's energy currency. Every step you take, every beat of your heart, every repair job your body runs is paid for in ATP minted inside mitochondria. The number and quality of your mitochondria determines how much you can do and how well you recover.

The first workout, and the bill

On August 27, Day 72 of this experiment, I did a hard workout after about ten days of doing almost nothing. Sixty-three minutes. My heart rate averaged 126.

The next morning my ketone number was 2.6. The morning after that, 2.6 again. The third day, 3.7. Then it climbed back into the 5s.

Three days below my floor from one workout.

So I did what I do. I sat down with the literature and I built an explanation. Then I wrote down a prediction. If my explanation was right, a second comparable workout, after a couple of weeks of regular training in between, should cost me less. A shallower dip. A shorter one. I put a date on it — the week of September 13 — and I told my readers about it before I knew the answer.

Then, on Saturday September 5, I ran for an hour. Not as the retest. That comes next week. Saturday was the "before." And it behaved exactly like August 27.

Two workouts, two dips, same shape. That is not a coincidence. That is a mechanism. Let me show you the machinery.

What actually happened inside

Think of your body as a house with two fuel systems.

The main line is glucose. It runs to every room. The backup generator is ketones. It kicks in when the main line goes quiet, and it happens to run the brain beautifully.

For most of this experiment I have been living on the generator. That is the whole point. My main line is turned down low on purpose, and the generator hums along at 5 or 6 on the meter.

Now I go out and run for an hour.

Hour one. Running muscles want fuel fast, and the fastest fuel is the sugar already packed inside them. The pantry. An hour of running empties a good part of that pantry. At the same time, working muscle also drinks ketones out of the blood. That is established — Balasse and Féry mapped it in 1989, and it has not been seriously challenged since. The liver is told to push glucose into the blood so the teaspoon of sugar in circulation does not crash. The main hormone pair for that dump is glucagon going up and insulin going down. Adrenaline is a supporting actor, not the lead — Wasserman's 2009 review is blunt about that. My continuous glucose monitor has watched the result: from the 70s at rest up into the low hundreds during a hard session. While muscle is pulling ketones and the liver is busy defending glucose, the meter can fall. This first phase lasts a couple of hours. It is the dip I have always seen.

Days one to three. This is the new part, and it has three layers.

Layer one: the pantry has to be refilled. An emptied muscle pantry is a priority for the body. It will not leave those shelves bare. After the run my glucose monitor sat a little higher than usual for a few days — 89, 106, 105, when my normal is the 70s. That is the liver still working.

How long does restocking take? For an athlete eating carbohydrate, about a day. For someone on a ketogenic diet, the pantry refills too — Volek's 2016 study of elite keto-adapted ultramarathon runners found their muscle glycogen dropped by about two thirds during a three-hour run and was still partly down two hours later, on much the same timeline as high-carb runners, even though they were burning fat at more than twice the peak rate. But they were trained. Their bodies had done this a thousand times and knew the drill. Mine had not. An untrained body on a low-carb diet restocks slowly, and it restocks by making glucose rather than eating it. That is gluconeogenesis — GNG — and it is a longer job. I will say plausible. It fits every number I have.

I will not say the liver "cannot make ketones while it makes glucose." In fasting those two jobs often rise together. What I can say is that from a high starting number, a restocking liver plus a higher glucose line is a fair suspect for a slower generator.

Layer two: one workout makes muscle more sensitive to insulin for two days. This one is established, and it has been for nearly forty years. In 1988, Mikines and colleagues put seven untrained men on a bike for an hour at 150 watts. Insulin-stimulated glucose uptake was higher immediately after the session and still higher 48 hours later. The effect was gone by day five. That is a good thing. It is why doctors tell you to exercise. The established fact is about muscle taking up sugar to rebuild the pantry. The leap is the next sentence. If the small amount of insulin I have now works harder, fat cells may hold on to fat rather than release it. Less fat released would mean less raw material reaching the liver. Less raw material would mean fewer ketones. That leap is plausible in a person already living above 4 on the meter. It is not what those 1988 clamps measured. I will not dress it up as proven.

Layer three: repair. A hard, unfamiliar workout tears muscle a little. That is normal. It is how muscle grows. Repair is an inflammatory job, and it runs for two or three days. This is the same window as the soreness. Cheung's 2003 review is the standard reference: the soreness rises over the first day, peaks between 24 and 72 hours, and resolves over about a week. So does the repair. So does my dip. They may be the same event seen from three angles. Alignment is not proof. It is a clue.

Stack those three layers on top of the first-hour dip and you get what I saw. A hard session, then three days of low numbers, then a return.

That is the deconditioning tax. The price a body charges for being asked to work after a long time of not working. In me it is paid in ketones, over three days, and it is refundable.

Why the textbooks say the opposite, and why I still believe mine

Now I have to argue against myself, because that is the deal I made with you.

There is a phenomenon in the old literature called post-exercise ketosis. Courtice and Douglas described it in 1936 after a long walk. In 1980 Koeslag, Noakes, and Sloan published the paper people still cite. And it says, in short, that after prolonged exercise, blood ketones often go up, not down. They peak about three hours later. The effect is stronger in some older people. A low-carbohydrate diet enhances it. A high-carbohydrate diet can wipe it out. The highest levels in that paper were in marathon runners who had deliberately stripped their glycogen first. One of them reached 3.88.

So by a careless reading of the book, a sixty-year-old on a ketogenic diet who empties his glycogen with an hour of running should have seen his meter rise.

Mine fell. For three days.

Here is why I think both can be true, and I want the certainty label to be loud.

Those papers measured a rise from near zero. Their subjects were not living at 5 on the meter. I was. A rise from 0.1 to 1.0 and a fall from 3.7 to 2.6 are not the same movie. During the work, muscle removes ketones from the blood. Afterward, the 48-hour insulin-sensitivity window and the restocking job can keep production from matching what I am used to. From a high floor, that looks like a dip.

I also have to tell you what the training data do not do for me. In some older work, untrained people got more post-exercise ketones than athletes, not fewer. In rats, training suppressed the post-exercise rise. So I will not claim the textbooks say "untrained livers make ketones fall." They do not. My untrained case is a hypothesis about a high baseline, not a quote from 1980.

There is one old clue that the ketone effect of work can last more than an afternoon. In 1909 Forssner found extra ketones in his urine for several days after a brisk walk on a low-carbohydrate diet. His arrow pointed up. Mine pointed down. The shared fact is duration. A body can keep paying a ketone bill for days after the session is over.

I want to be clear about the strength of that claim. The 48-hour insulin effect, established. The soreness window, established. Ketone uptake by working muscle, established. The liver defending blood glucose during exercise, established. That an untrained low-carb body already living above 4 pays this as a three-day ketone dip, plausible. That is my hypothesis, built on two observations in one person. I will not say proven. I will say I predicted it once and it came true once. Next week I try to make it come true a third time, in a specific direction.

The dehydration wrinkle — and the cortisol chain

There is one more piece I have to put on the table, because it may explain part of what happened, and because it is the part I did not see coming.

I have had four dehydration episodes this summer. I have written about them. I am prone to orthostatic changes — my blood pressure drops when I stand, which is a sign my fluid tank is running low. I did not connect this to the ketone dip until I sat down to write this letter and started pulling the papers.

Here is the chain, and every link has a study behind it.

Dehydration raises cortisol. This is established. Zaplatosch and Adams pooled twenty-one studies in 2020: acute hypohydration — whether from exercise, heat, or both — significantly raises cortisol in humans. Castro-Sepulveda's 2018 study of runners found that the most dehydrated subjects — down 5% of body weight — showed significantly greater cortisol increases after exercise than hydrated controls. Even habitual low fluid intake without acute exercise raises baseline cortisol reactivity to stress, as Kashi showed in 2025. A body short on fluid is a body running on stress hormones.

Cortisol tells the liver to make glucose. This is established, and has been since the 1990s. Fujiwara's 1996 study showed that cortisol infusion sustains hepatic gluconeogenesis — the liver keeps making glucose from scratch as long as cortisol is elevated. Cortisol also tells muscle to break down protein into amino acids, which become the raw material for that gluconeogenesis. The whole system is designed to keep blood glucose up during stress.

More glucose means more insulin. The pancreas responds to rising glucose by releasing insulin. That is basic physiology.

More insulin means fewer ketones. Insulin is the master switch. When insulin is up, the liver stops making ketones and starts storing fuel. This is the fundamental toggle between the glucose system and the ketone system.

So the chain runs: dehydration → orthostatic stress → cortisol up → gluconeogenesis up → glucose up → insulin up → ketone production down.

I cannot prove this chain explains my three-day dip. I did not measure cortisol. I did not measure insulin. But I was dehydrated. I know that from the orthostatic changes. And the chain is plausible — every link is a published finding. I am putting it on the record as a contributing suspect, not the sole defendant.

If it is right, it has a practical implication I should have seen sooner: on a ketogenic diet, staying hydrated is not just about avoiding cramps. It is about keeping cortisol down, which keeps insulin down, which keeps the generator running. The water bottle is a ketone tool.

The liver's double shift — how GNG and ketogenesis work together

Now I want to pull back from the knee and look at the liver, because the liver is doing something remarkable, and I do not think it gets enough credit.

Your liver is running two factories at the same time. Factory one is gluconeogenesis — GNG — making glucose from scratch. Factory two is ketogenesis — making BHB from fat. Both factories run simultaneously. Both are essential. And they serve different customers.

GNG makes glucose for the tissues that absolutely need it. Your red blood cells have no mitochondria — they cannot burn fat or ketones, only glucose. Parts of your kidney and your brain need glucose too, at least some of the time. During exercise, your muscles burn through their glycogen pantry and then need glucose from the blood to keep going. GNG is the supply line.

Ketogenesis makes BHB for the tissues that can use it. Your brain, your heart, your muscles, your kidneys — they all burn BHB beautifully when it is available. And your joints — I go through this tissue by tissue in the companion piece — may benefit from BHB not just as fuel but as a signal — the inflammasome blockade, the HCAR2 activation, the HDAC inhibition.

Here is what is remarkable: these two factories do not just coexist. They cooperate. GNG uses the same raw materials — amino acids, glycerol, lactate — that would otherwise pile up. Ketogenesis uses fat. The liver is running a dual-fuel operation, feeding glucose to the tissues that need it and BHB to the tissues that can use it, simultaneously, from different raw materials, without missing a beat.

During my run on Saturday, this is what was happening. My muscles were burning through their glycogen. My liver was making glucose via GNG to keep blood sugar from crashing. At the same time, it was making BHB to feed my brain and heart. Both factories running. Both essential.

And here is the part that matters for the knee: while the GNG factory is making glucose for the muscles, the ketogenesis factory is making BHB that circulates to every tissue in the body — including the lining, the cartilage and the bone of a knee. The BHB is not just fuel for those tissues. It is a signal. It is telling the macrophages in the synovium to stand down. It is telling the chondrocytes to clean up their mitochondria. It is telling the osteoblasts in the bone to keep building.

The liver is not just a fuel depot. It is a pharmacy. And on a ketogenic diet, it is dispensing anti-inflammatory medication with every shift.

The mitochondrial question — do BHB and exercise build power plants through different doors?

This is the part I find most interesting, and it is the part where the science is most active right now.

Both BHB and exercise increase mitochondria. That much is established. But they do it through different mechanisms, and the question of whether they are synergistic — whether together they do more than the sum of their parts — is one of the most interesting open questions in metabolic science.

Exercise builds mitochondria through PGC-1α. This is the classic pathway, mapped over decades. When you exercise, your muscles experience energy stress — ATP drops, AMP rises. An enzyme called AMPK — the cell's fuel gauge — detects this and activates PGC-1α, the master foreman for mitochondrial construction. PGC-1α turns on the genes for building new mitochondria. More mitochondria means more ATP production, more fat burning, more endurance. This is why exercise works. It is established in humans, in animals, in cells. It is one of the most solid findings in exercise physiology.

BHB builds mitochondria through a different set of doors. And this is where it gets interesting, because BHB does not just walk through the PGC-1α door. It uses at least three separate entrances.

Door one: HDAC inhibition. Remember Shimazu's 2013 paper. BHB blocks HDACs, which unshelves FOXO3A. FOXO3A does not just protect against oxidative stress. It also promotes mitochondrial quality control — the identification and removal of damaged mitochondria, and the production of new ones. This is an epigenetic mechanism — it works by changing which genes are available for reading, not by changing the genes themselves. Exercise does not use this door. BHB does.

Door two: HCAR2 activation. When BHB docks at HCAR2 on the cell surface, it triggers a signaling cascade that includes AMPK activation. Wait — that is the same AMPK that exercise activates. So here the two pathways converge. But they arrive at AMPK from different directions. Exercise activates AMPK by creating energy stress inside the cell. BHB activates it from outside, through the receptor. Same destination, different road.

Door three: direct mitochondrial effects. BHB is not just a signal. It is a fuel. And it is a cleaner fuel than glucose in one specific way: it produces fewer reactive oxygen species — fewer sparks — per unit of ATP. This means less oxidative damage to the mitochondria themselves, which means the existing mitochondria last longer and work better. You are not just building new power plants. You are protecting the ones you have. Exercise does not do this directly. Exercise actually increases ROS production in the short term — that is part of the signal that triggers adaptation. BHB reduces it.

So the answer to the synergy question is: probably yes, and here is why. Exercise and BHB activate overlapping but distinct pathways. Exercise stresses the system and triggers adaptation through PGC-1α. BHB protects the system and triggers adaptation through HDAC inhibition and HCAR2. Exercise makes more sparks in the short term, which is the signal for growth. BHB cleans up the sparks, which is the signal for survival. Together, you get the growth signal without the damage. That is synergy — not just addition.

I want to be careful here. This specific synergy — exercise plus BHB for mitochondrial biogenesis — has not been tested in a controlled human trial. The individual mechanisms are established. The synergy is a hypothesis built on those mechanisms. I will say plausible.

But there is one mouse study that points in the right direction. In 2020, Monsalves-Alvarez and colleagues gave BHB to mice and measured their exercise capacity and mitochondrial function. The BHB-supplemented mice ran longer and had changes in mitochondrial morphology and function consistent with improved mitochondrial health. The BHB alone improved exercise capacity. Add actual exercise training to that, and you would expect more. That study is the closest thing we have to a synergy demonstration. It is in mice. It is not in humans. But it is a real paper, and it points the right way.

Does any of this make you faster?

The honest answer is: it depends on what you mean by faster, and the evidence is genuinely mixed.

For endurance — long, steady effort — the evidence is favorable. Volek's 2016 study of keto-adapted ultramarathon runners showed they could burn fat at 2.3 times the rate of high-carb runners. That is a massive increase in the size of the fuel tank. Fat stores are essentially unlimited — even a lean athlete carries tens of thousands of calories of fat. Glycogen stores are a few thousand calories at most. If you can burn fat efficiently, you can go farther before hitting the wall. For ultramarathons, for long hikes, for anything measured in hours, keto-adaptation is an advantage.

For high-intensity, short-duration effort — sprinting, surging, going up a hill fast — the evidence is negative. This is the part the keto community does not like to talk about. A 2021 review by Louise Burke, the Australian Institute of Sport's chief of nutrition, concluded that while keto-adaptation increases fat oxidation dramatically, it impairs the ability to use carbohydrate for high-intensity work. The reason is mechanistic: keto-adaptation downregulates an enzyme called pyruvate dehydrogenase — PDH — which is the gatekeeper for burning glucose. Less PDH activity means less glucose burning, which means less power at high intensity. Burke's conclusion was blunt: for events that require high-intensity surges — which is most competitive sports — keto-adaptation is a liability.

For exogenous ketones — drinking BHB as a supplement before exercise — the evidence is also mixed and mostly negative for performance. Cox's 2016 study initially showed a 2% improvement in cycling time trial performance with a ketone ester drink. But Leckey's 2017 study in professional cyclists found that a ketone diester impaired 31-kilometer time trial performance. O'Malley's 2017 study found that ketone salts increased fat oxidation but impaired high-intensity performance. The pattern is consistent: raising blood BHB acutely before exercise does not reliably improve performance and may impair it, possibly because the sudden BHB flood suppresses the body's own fat burning and glycogen use.

So does ketosis make you faster? For long, slow distance: probably yes, once adapted. For sprinting and surging: probably no. For acute supplementation: the evidence says no or maybe slightly negative.

But here is the thing. I am not trying to win a race. I am trying to run for an hour without my knees sending a bill. And for that — for the ability to move, consistently, without pain — the equation is different. The question is not "does BHB make me faster." The question is "does BHB let me run at all." And on that question, I have one data point, and it is Saturday.

The prediction, on the record

From September 5 I am exercising every day. Not hard every day. But out the door every day. If the deconditioning tax is real, then after two weeks of regular training, three things should be different when I repeat a comparable workout the week of September 13.

One. The dip should be shallower. My muscles will have a bigger, better-managed pantry, so a workout will not empty it so completely, and the restocking order will be smaller.

Two. The dip should be shorter. Two days instead of three. Maybe one.

Three. The soreness should be milder. A trained muscle tears less from the same effort.

I am adding a fourth prediction, now that I have the dehydration piece.

Four. If I stay hydrated — genuinely hydrated, not "I had a glass of water" hydrated — the dip should be even smaller, because the cortisol chain will not be contributing.

If all four happen, I have a named finding, in one person, with a prediction on record ahead of time. If they do not happen, I will publish that too, and I will have learned that the tax is not about conditioning, or not only about conditioning. Either answer is worth having. What I will not do is decide after the fact what I expected.

And the knees. I will keep filming the stairs. If the knees hold up through two weeks of daily exercise, that is not proof. But it is another data point on the line.

We will see what happens by the end of the 180-day experiment. I am at Day 86 as of today, September 10, 2026. Ninety-four days to go. The knees are holding. The meter is recovering. And I ran for an hour.

What I'd do with this, if I were you

If you are living on the generator and you decide to start moving again, expect the tax. Two or three days of a lower number after a hard or unfamiliar session. It is not the diet failing. It is not drift. It is your liver doing a restocking job, and possibly your adrenal glands doing a stress job on top of it.

Do not fix it by eating differently. Do not panic and change three things. Drink your water. Take your salt. Sleep. Measure every morning so you can watch it come back. And then, if the model is right, do it again in two weeks and watch it cost you less.

The number is a thermometer, not a verdict. It is telling you what your liver is doing today. What your liver is doing today after an hour of running is exactly what it should be doing.

I ran for an hour. It cost me three days on the meter. It was worth it — and the knees are the other half of that story: /blog/what-a-ketone-does-inside-a-knee

— Barry

I post my blood ketone number every day — including the bad ones — in a 90-second video: youtube.com/@neuraliftmd. Day one is there. So is every failure since.

If you want to do something like this with a physician watching, I'm taking on a small founding cohort. It starts with a conversation: calendly.com/hello-neuralift/30min

Educational only, not medical advice. Talk to your doctor before changing your diet, medications, or exercise.

Where all this comes from

1. Koeslag JH, Noakes TD, Sloan AW. Post-exercise ketosis. Journal of Physiology 1980;301:79–90. — Blood ketones rise after prolonged exercise, peaking about three hours later; effect larger in older and low-carb subjects; highest values in glycogen-stripped marathoners (3.88 mmol/L). The "textbook" response that runs opposite to mine. Verified.
2. Courtice FC, Douglas CG. The effects of prolonged muscular exercise on the metabolism. Proceedings of the Royal Society B 1936;119:381–439. — Original description of ketones rising after long exercise. Verified.
3. Forssner G. Über die Einwirkung der Muskelarbeit auf die Acetonkörperausscheidung bei kohlenhydratarmer Kost. Skandinavisches Archiv für Physiologie 1909;22:393–405. — On a low-carb diet, ketonuria increased after a brisk 4 km walk and persisted for several days. Evidence that a ketone effect of exercise can last days. Verified via Koeslag 1980.
4. Mikines KJ, Sonne B, Farrell PA, Tronier B, Galbo H. Effect of physical exercise on sensitivity and responsiveness to insulin in humans. American Journal of Physiology 1988;254(3 Pt 1):E248–E259. — Seven untrained men, one hour of cycling. Insulin-stimulated glucose uptake higher immediately and at 48 hours; gone by day 5. Source for the 48-hour insulin sensitivity window. Verified.
5. Cheung K, Hume PA, Maxwell L. Delayed onset muscle soreness: treatment strategies and performance factors. Sports Medicine 2003;33(2):145–164. — DOMS rises over the first day, peaks at 24–72 hours, resolves in about a week. Caused by small tears and repair response, not lactic acid. Verified.
6. Volek JS, Freidenreich DJ, Saenz C, et al. Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism 2016;65(3):100–110. — Twenty elite ultra-runners. Peak fat oxidation 2.3-fold higher in low-carb group. Muscle glycogen fell 64% after 180 min running, still 36% below pre-exercise at 120 min recovery. Trained low-carb bodies restock glycogen on a similar timeline to high-carb athletes. Verified.
7. Balasse EO, Féry F. Ketone body production and disposal: effects of fasting, diabetes, and exercise. Diabetes/Metabolism Reviews 1989;5(3):247–270. — Classic review: liver makes ketones, muscle removes them; exercise increases ketone disposal during effort. Verified.
8. Wasserman DH. Four grams of glucose. American Journal of Physiology – Endocrinology and Metabolism 2009;296(1):E11–E21. — The liver defends blood glucose during exercise mainly by glucagon rising and insulin falling. Adrenaline is a supporting actor, not the lead. Verified.
9. Zaplatosch ME, Adams WM. The effect of acute hypohydration on indicators of glycemic regulation, appetite, metabolism and stress: a systematic review and meta-analysis. Nutrients 2020;12(9):2526. — 21 studies; cortisol significantly elevated with hypohydration (insulin unaffected). Source for dehydration → cortisol link. Verified (citation corrected Sep 16, 2026).
10. Castro-Sepulveda M, et al. Basal mild dehydration increase salivary cortisol after a friendly match in young elite soccer players. Frontiers in Physiology 2018;9:1347. — Most dehydrated subjects (−5% body weight) showed significantly greater cortisol increases after exercise. Verified.
11. Kashi DS, Hunter M, Edwards JP, et al. Habitual fluid intake and hydration status influence cortisol reactivity to acute psychosocial stress. Journal of Applied Physiology 2025;139(3):698–708. — Adults with habitual low fluid intake show greater cortisol reactivity to stress. Even chronic mild underhydration raises the cortisol baseline. Verified.
12. Fujiwara T, Cherrington AD, Neal DN, McGuinness OP. Role of cortisol in the metabolic response to stress hormone infusion in the conscious dog. Metabolism 1996;45(5):571–578. — Cortisol infusion sustains hepatic gluconeogenesis during stress. Source for cortisol → liver glucose production. Verified.
13. Shimazu T, Hirschey MD, Newman J, et al. Suppression of oxidative stress by β-hydroxybutyrate, an endogenous histone deacetylase inhibitor. Science 2013;339(6116):211–214. — BHB inhibits HDACs 1, 3, and 4, upregulating FOXO3A and MT2, which increases oxidative stress resistance. Demonstrated in mouse kidney; mechanism is general. Cited over 2,200 times. Verified.
14. Graff EC, Fang H, Wanders D, Judd RL. Anti-inflammatory effects of the hydroxycarboxylic acid receptor 2. Metabolism 2016;65(2):102–113. — HCA2 (HCAR2) activation produces broad anti-inflammatory effects across multiple tissues. Verified.
15. Monsalves-Alvarez M, et al. β-Hydroxybutyrate increases exercise capacity associated with modifications in mitochondrial morphology and function in mouse skeletal muscle. Nutrients 2020;12(7):1930. — BHB supplementation increased exercise capacity and improved mitochondrial morphology/function in mouse skeletal muscle. Closest study to BHB-exercise synergy. In mice. Verified.
16. Burke LM. Ketogenic low-CHO, high-fat diet: the future of elite endurance sport? Journal of Physiology 2021;599(3):819–843. — Keto-adaptation increases fat oxidation but impairs glycolytic capacity via PDH downregulation; a liability for high-intensity efforts. Verified.
17. Cox PJ, Kirk T, Ashmore T, et al. Nutritional ketosis alters fuel preference and thereby endurance performance in athletes. Cell Metabolism 2016;24(2):256–268. — Ketone ester drink improved cycling time trial by ~2%. Verified.
18. Leckey JJ, Ross MLR, Quod M, Hawley JA, Burke LM. Ketone diester ingestion impairs time-trial performance in professional cyclists. Frontiers in Physiology 2017;8:806. — Ketone diester impaired 31 km time trial in professional cyclists. Counterevidence to Cox. Verified.
19. O'Malley T, Myette-Côté É, Durrer C, Little JP. Nutritional ketone salts increase fat oxidation but impair high-intensity exercise performance in healthy adult males. Applied Physiology, Nutrition, and Metabolism 2017;42(10):1031–1035. — Ketone salts increased fat oxidation but impaired high-intensity performance. Verified.
20. My own record. Aug 27 workout: 63 min, average HR 126, next three mornings 2.6 / 2.6 / 3.7, glucose 89 / 106 / 105. Sep 5 run: approximately 1 h 15 min total session, 3.7 miles running continuous, 5 miles total including walking; readings 3.7 before, 3.3 after, 3.1 / 2.6 / 3.6 over the next 36 hours. Sleep tracker nervous-system score at the floor of its scale the night after. Baseline symptom scorecard, June 2026: knees 10 of 10. Orthostatic blood pressure changes noted this summer; four dehydration episodes.