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The book in one minute
Dave Asprey is a technology entrepreneur, not a neuroscientist and not a physician. He founded the Bulletproof company and is the reason people put butter in coffee.
The claim here is narrower than in his later book, and in one respect more testable. Your brain is about 2% of your body weight and consumes roughly 20% of your energy. That energy comes from mitochondria. Therefore, Asprey argues, the ceiling on your thinking is set by mitochondrial output - not by intelligence, training or willpower, but by supply. And most people's supply is quietly degraded by what they eat, breathe, and how they sleep and light their lives.
The everyday experience of that degradation is the thing everyone recognises: the afternoon fog, the word that will not come, the meeting you cannot follow. Fix the supply, he says, and the fog lifts - in two weeks.
The biology in the first part of the book is real. The bridge from it to the promise is the author's own, and it carries more weight than it can bear.
Where the established science stops
The book does not separate textbook fact from argument, so this summary will. The distinction is the single most useful thing to hold on to while reading it.
Brain fog: what to rule out first
This is the most important section on this page and it is not in the book, which is exactly why it needs saying.
Brain fog is not a diagnosis. It is a symptom, it is extremely common, and it is produced by a long list of conditions - several serious, all treatable once identified, and nearly all found with a conversation and a blood test.
- Sleep apnoeaBadly underdiagnosed, and it produces exactly the pattern of daytime fog and poor concentration the book describes.
- Underactive thyroidCommon, easily tested, easily treated.
- Iron deficiencyWith or without anaemia. Common in menstruating women.
- B12 deficiencyCommon in vegetarians, in people over 60, and in anyone on long-term metformin or acid-suppressing drugs.
- DepressionVery often presents as cognitive dullness rather than sadness.
- Poorly controlled blood glucoseIncluding undiagnosed insulin resistance.
- Perimenopause, long covid, medication side effectsAntihistamines, sedatives and some blood-pressure drugs are frequent culprits.
- Ordinary chronic sleep deprivationThe most common cause of all, and the one people are least willing to accept.
The risk in a book like this is not that its advice is harmful - most of it is not. The risk is delay: someone with untreated sleep apnoea spending eight months on light panels and supplements, feeling slightly better each time they change something, and never getting the diagnosis that would actually fix it.
The protocol
Diet and the fuel argument Mechanism yes, outcome no
The Bulletproof diet with the brain as its justification: high fat, low carbohydrate, moderate protein, vegetables in volume. The reasoning offered is fuel stability - glucose delivery is uneven, ketone delivery steadier, and the swings are what produce the crashes.
The most scientifically interesting claim is ketones as an alternative brain fuel. The brain genuinely can run on ketone bodies as well as glucose; this is not disputed, and there has been real research into whether medium-chain triglycerides help in Alzheimer's disease, with modest and mixed results and some signal in patients without a particular genetic variant. It is a live question. The leap to a healthy person thinks measurably better is not tested.
Then the "kryptonite" list: sugar, industrial seed oils, and foods he considers high in mould toxins. The first two are reasonable advice for unglamorous reasons. The third is the mycotoxin argument, which is not well supported for ordinary food and is attached to a product line.
Oxygen and breathing Free version worth it
One of the more distinctive sections. The physiology underneath is real and often misunderstood: oxygen release from haemoglobin into tissue is promoted by carbon dioxide - the Bohr effect - so chronic over-breathing lowers CO2 and can reduce delivery, which is why hyperventilating makes people light-headed rather than energised.
From this come nasal breathing, slower breathing, breath holds, and intermittent hypoxic training. Nasal and slow breathing have reasonable support for autonomic and stress effects and cost nothing. Breath work as a route to better cognition is thin. Intermittent hypoxic training is real and studied in athletic contexts, but the equipment is expensive and doing it badly is not harmless.
Light Solid, then speculative
Solid: light is the primary circadian signal, evening blue suppresses melatonin, morning brightness anchors the clock, and circadian disruption impairs cognition and mood. Free, easy, genuinely worth doing.
Middle: red and near-infrared exposure, on the argument that these wavelengths are absorbed by an enzyme in the mitochondrial respiratory chain. The mechanism is real and underpins photobiomodulation, which has decent evidence for local uses in skin and wound healing. Applying it to the brain through the skull is a research area, not a settled treatment, and the trials are small.
Speculative: that ordinary indoor lighting is actively harmful rather than merely circadian-disruptive, and that deliberate ultraviolet exposure matters for brain function. The evidence is not there, and UV carries a well documented cost of its own.
Sleep Well supported
The strongest chapter, as in his later book, because the recommendations and the science agree. The mechanism is glymphatic clearance: during sleep, particularly deep sleep, the spaces between brain cells expand and cerebrospinal fluid moves through the tissue carrying away metabolic waste including amyloid-beta. This reframes sleep from rest to maintenance.
The advice is conventional and correct - consistent timing, cool dark room, no alcohol near bed because it fragments sleep architecture and suppresses REM even while shortening sleep onset, caffeine cut off early given a half-life of roughly five to six hours that varies genetically, morning daylight.
The caution he does not give: consumer sleep trackers estimate stages from movement and heart rate, are unreliable night to night, and there is a documented pattern of people becoming anxious about their sleep scores in a way that measurably damages their sleep. If tracking makes you worse, stop.
Exercise Best evidence in the book
It gets less room than it deserves. The mechanism Asprey highlights is BDNF, a protein involved in the growth and survival of neurons, which exercise raises - this is well established. Beyond that, activity improves cerebral blood flow, insulin sensitivity and sleep, and the association between physical activity and reduced dementia risk is one of the more consistent findings in the field.
A reader who did only this chapter and ignored the rest of the book would capture most of the available benefit for none of the cost.
Neurofeedback and the expensive tier
Every Asprey book has a tier most readers cannot and should not follow. Here it is largely neurofeedback: brain electrical activity measured and displayed back in real time, with the claim that training produces lasting changes in attention and cognition. Asprey is a heavy advocate, and he runs an intensive neurofeedback programme costing many thousands of dollars, described at length.
The evidence position, stated carefully: neurofeedback has been studied for decades, particularly in ADHD. Reviews using properly blinded, sham-controlled designs generally find the specific effects small and hard to separate from placebo and from the non-specific benefits of sitting still and concentrating for many hours. It is not fraudulent, and it is not established.
Alongside it sit extensive lab panels, hyperbaric oxygen, assorted devices and a long supplement list. The pattern is the same as in Super Human: the cheap interventions are the well-supported ones, the expensive ones are the speculative ones, and the book's enthusiasm is distributed in almost exactly the wrong proportion to the evidence.
The two-week programme
The last part assembles everything into a fortnight: remove the problem foods, compress the eating window, add the fats and supplements, impose sleep discipline and morning light, add breath work and exercise, measure before and after.
Two honest observations about this format.
Two weeks cannot tell you what the book says it will. It is precisely the window in which placebo is strongest, in which practice effects inflate any repeated cognitive test, and in which regression to the mean does most of its work - because people start these programmes when they feel worst. Everyone who completes a fortnight of deliberate self-improvement feels better at the end, and that tells you nothing about which component did anything.
Changing fifteen variables at once means you cannot learn which mattered. Genuine self-experimentation means changing one thing, holding it for several weeks, and measuring. That is slower, far less marketable, and the only version that produces knowledge.
The programme is a good way to feel better for a fortnight. It is a poor way to find out why.
What holds up, and what does not
Holds up
Do these. They are free.
Sleep quality and consistency. Aerobic exercise and resistance training - the best-evidenced thing in the book by a distance. Morning light, less light at night. Steady blood glucose. Nasal and slower breathing. Correcting genuine deficiencies. And getting the medical causes of fog ruled out first.
Plausible, unproven
One at a time, if at all.
Ketones and MCT oil for cognition in healthy people. Red and near-infrared light beyond local tissue effects. Cold exposure. Breath holds and intermittent hypoxic training. Polyphenols. Most of the supplement stack past the basics.
Does not hold up
Leave alone.
The two-week promise as anything more than marketing. The mould-toxin claims about ordinary coffee. The electromagnetic field concerns. Commercial neurofeedback as an established intervention. And the habit of presenting a mechanism as though it were a demonstrated human outcome.
The commercial position
This applies more sharply here than in Super Human. The protocol routes through products Asprey sells: the recommended fat is his branded C8 oil, the recommended coffee is his coffee - justified by a mould-toxin argument the evidence does not support - the recommended neurofeedback is his facility, and several supplement categories are his.
None of that proves any claim false. People generally build businesses around things they believe, and belief usually comes first. But the density of product-adjacent recommendation here is high enough that a reader should keep a running note of which advice is free and which is purchasable.
The pattern across both books is consistent and clarifying: the free advice is the well-supported advice - sleep, movement, morning light, not eating rubbish, getting a blood test - and the purchasable advice is where the evidence thins. That correlation is not an accusation. It is a very useful filter.
Common questions
Should I read this or Super Human?
They overlap heavily. Super Human is broader and later; Head Strong is narrower, earlier and specifically about cognition. If you want the ageing argument, read Super Human. If your actual question is "why is my thinking foggy", read this one - but read the rule-out list first. Do not expect the second book you pick up to be new.
Does the two-week claim hold up?
Not as evidence. A fortnight is the window where placebo, practice effects on repeated tests, and regression to the mean are all at their strongest, and the programme changes many variables simultaneously. People do generally feel better after two weeks of deliberate effort. That is not the same as the mechanism being demonstrated.
Is there anything to the mitochondria argument at all?
Yes, at the level of biology. Mitochondrial dysfunction is a serious research area in neurodegeneration, and severe mitochondrial disorders are real and devastating. What has not been shown is that mitochondrial output is the limiting factor on ordinary day-to-day thinking in a healthy adult, or that the interventions in this book raise it in a way that changes cognition.
What is worth doing if I only do one thing?
Exercise, particularly aerobic. It has more evidence behind it than anything else in the book, it is free, and it also improves sleep, blood glucose and mood - three of the other levers the book pulls at greater expense.
About this summary. This is an original summary and commentary on Head Strong: The Bulletproof Plan to Activate Untapped Brain Energy to Work Smarter and Think Faster, in Just Two Weeks by Dave Asprey (Harper Wave, 2017), written and narrated for the AIEIO book library. It paraphrases the book's ideas and contains no reproduced text. ⚠ The summary is arranged by topic rather than by chapter, because the individual chapter titles and their numbering could not be confirmed with confidence. Evidence ratings on this page are our own assessment and are labelled as such. Nothing here is medical advice.
Not affiliated. AIEIO is not affiliated with, authorised by, or endorsed by the author, the publisher, or any rights holder. Book titles and author names are used only to identify the work being summarised. No text, cover artwork or audio from the book is reproduced here - the summary is original writing and the narration is of that writing.
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