What you've heard
Popular health claims, graded
The claims people repeat most, each tested against the evidence rather than against how often it is said. Every one carries the book's verdict and its evidence grade, and several verdicts run against the popular version.
The chapter's table of nine claims that travel under the ancestral banner.
- The claim: Avoid seed oils to lower inflammationAre seed oils inflammatory? What the trials showEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Against, as stated.Also tested in Chapter 5: Seed oils such as soybean, corn and canola are inflammatory poisons behind modern disease
- The claim: Drink raw milkIs raw milk healthier or safe?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Against, and the risk is measured.Also tested in Chapter 6: Raw milk is healthier
- The claim: Grounding, or earthingDoes grounding work, or is it pseudoscience?Evidence grade: Emerging. Early, small, animal-only, or actively contested.Emerging and contested.Also tested in Chapter 10: Walking barefoot on the earth, or sleeping on a grounding mat, lets electrons flow into your body and reduces inflammation
- The claim: Carnivore dietIs the carnivore diet supported by evidence?Evidence grade: Emerging. Early, small, animal-only, or actively contested.Self-reported only, no trials.
- The claim: Mouth tapingIs mouth taping safe, and does it work?Evidence grade: Emerging. Early, small, animal-only, or actively contested.Unsupported, with a safety catch.Also tested in Chapter 8: Taping your mouth shut at night improves sleep and breathing
- The claim: Barefoot and minimal shoesDo barefoot shoes fix your feet?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Probable for foot strength; unsupported for injury prevention.Also tested in Chapter 3: Barefoot or minimalist shoes fix your feet
- The claim: Cold plungesDo cold plunges do anything?Evidence grade: Emerging. Early, small, animal-only, or actively contested.A narrow effect on heat regulation; nothing on fat loss.
- The claim: Avoid sunscreenIs sunscreen bad for you?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Against: the one trial runs the other way.Also tested in Chapter 7: Sunscreen is dangerous, and you are better off without it
- The claim: Detox teas, juice cleanses and similarDo detox teas and juice cleanses work?Unsupported.
Chapter 3
The Body That Walks
- What you've heard: Sitting is the new smokingIs sitting the new smoking?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Exaggerated about tenfold. Break up sitting, but above all, move more.
- What you've heard: You need 10,000 steps a dayIs 10,000 steps a day a myth? How many steps you actually needEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.A round number, not a threshold.
Chapter 4
Load, Strength and Bone
- What you've heard: An ice bath after lifting helps you recoverDoes a cold plunge after lifting hurt muscle growth?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Wrong if building muscle is the goal.
- What you've heard: More protein is always betterIs more protein always better?Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.False. Past a point, extra protein stops adding muscle.
Chapter 5
Eat
- What you've heard: Everyone should wear a glucose monitor to find their spikesShould people without diabetes wear a glucose monitor?Evidence grade: Emerging. Early, small, animal-only, or actively contested.No evidence of benefit for people without diabetes. A curiosity, not a health tool, and no substitute for a blood test.
- What you've heard: Drink at least eight glasses of water a dayIs 8 glasses of water a day a myth?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.False as a rule. Drink to thirst, more in heat and hard exercise, and never past thirst in long events.
Chapter 6
The Gut That Expects Dirt
- What you've heard: Probiotic pills fix your gutDo probiotic pills fix your gut?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.For healthy people, unsupported; spend the money on yogurt and beans.
- What you've heard: A scoop of greens powder covers your vegetablesCan a greens powder replace vegetables?Evidence grade: Emerging. Early, small, animal-only, or actively contested.Expensive vitamins, and no substitute for vegetables.
- What you've heard: A "leaky gut" is behind your symptomsIs leaky gut real?Evidence grade: Emerging. Early, small, animal-only, or actively contested.Real in specific diseases, unproven as an everyday diagnosis.
Chapter 7
Light and Dark
- What you've heard: Blue-blocking glasses protect your sleep from screensDo blue light glasses work for sleep?Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Mostly unsupported; skip the glasses unless a clinician suggests them for a specific sleep problem.
- What you've heard: Ten minutes of morning sunlight sets your body clock for the dayDoes ten minutes of morning sunlight set your body clock?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Right direction, invented number. Get outside early, and stay longer when it is gray.
Chapter 8
Sleep
- What you've heard: Wait 90 minutes after waking before your first coffeeShould you wait 90 minutes after waking for coffee?Evidence grade: Emerging. Early, small, animal-only, or actively contested.Untested, and the reasoning looks backward. Drink your coffee when you like it in the morning; the timing that matters is the hours before bed.
- What you've heard: Tart cherry juice and magnesium will fix your sleepDo tart cherry juice and magnesium help you sleep?Evidence grade: Emerging. Early, small, animal-only, or actively contested.Unproven. The juice adds sugar, and magnesium is a long shot, not a treatment.
- What you've heard: NSDR or yoga nidra can stand in for lost sleepCan NSDR or yoga nidra replace lost sleep?Evidence grade: Emerging. Early, small, animal-only, or actively contested.A pleasant way to rest, not a substitute for sleep.
Chapter 9
Heat and Cold
- What you've heard: Brown fat will make you leanDoes a cold plunge burn fat? Brown fat, sized honestlyEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Oversold. Mild cold may nudge insulin sensitivity in tiny trials, but it will not move your weight.
- What you've heard: Cold water raises dopamine by 250%Does a cold plunge raise dopamine 250%? The study behind the numberEvidence grade: Emerging. Early, small, animal-only, or actively contested.A real number, misapplied. Enjoy the jolt if you like it, without expecting a chemical dose.
- What you've heard: Eleven minutes of cold and fifty-seven minutes of heat a week is the optimal protocolIs 11 minutes of cold and 57 of heat a week optimal?Evidence grade: Emerging. Early, small, animal-only, or actively contested.Not a protocol.
Chapter 10
Green and Quiet
Chapter 12
Attention in the Age of the Phone
- What you've heard: A digital detox resets your brainDoes a digital detox reset your brain?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.A planned break brings a small lift and can reset a habit; "resets your brain" is overstated.
- What you've heard: Screen time is destroying a generationIs screen time destroying a generation?Evidence grade: Emerging. Early, small, animal-only, or actively contested.Unproven as stated, with a serious case on both sides; heavy use is a fair worry, and the causal claim is open.
Chapter 13
Stress and the Mind
- What you've heard: Chronic stress wears out your adrenal glands, a condition called adrenal fatigue, and saliva tests and adrenal supplements can fix itIs adrenal fatigue real?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.False. If you are exhausted, see a clinician rather than the supplement aisle.
- What you've heard: The physiological sigh, two inhales through the nose and a long exhale through the mouth, is the fastest proven way to calm downThe physiological sigh: what the evidence showsEvidence grade: Emerging. Early, small, animal-only, or actively contested.A reasonable quick reset with thin evidence; "fastest" and "proven" are overstated.
- What you've heard: Breathwork will fix your anxietyCan breathwork fix anxiety?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Helps a little; not a substitute for therapy or medication.
Chapter 14
Wanting, Loving, Losing, Meaning
- What you've heard: A dopamine fast resets your brainDoes a dopamine detox actually work?Evidence grade: Emerging. Early, small, animal-only, or actively contested.The name misreads the science, and the behavior can help. Take a month off something that has stopped feeling like a choice, and skip the day-long fasts.
- What you've heard: Rat Park proved addiction is about the cage, not the drugDid Rat Park prove addiction is about the cage?Evidence grade: Emerging. Early, small, animal-only, or actively contested.Overstated. Environment matters a great deal, as the Vietnam veterans show, but the cage is not the whole story: drugs are rewarding in any cage.
Chapter 15
Women's Bodies Across the Life Course
- What you've heard: Sync your workouts to your cycle: lift heavy in the first half, go easy in the secondDoes cycle syncing your workouts work?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Not supported. Train consistently and adjust on days you feel bad, whatever the reason.
- What you've heard: Hormone therapy causes breast cancerDoes hormone therapy cause breast cancer?Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Partly true and badly overstated. The risk is real, modest and depends on type and duration. It argues for a careful choice of treatment; it does not argue for refusing one.
Chapter 16
Aging Well
- What you've heard: Every man over forty should be on testosteroneShould men take testosterone after 40?Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.False.
- What you've heard: An epigenetic age test tells you how fast you are agingCan an epigenetic age test tell you how fast you are aging?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Not reliable for individuals.
- What you've heard: NAD+ boosters and other longevity supplements slow agingDo NAD+ supplements work?Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Unsupported so far.
How to judge a claim like these yourself
The first rule decides most cases: find the primary study. If none exists, or the one you find measured something else, the claim is unsupported however often it is repeated. Chapter 2 of the book sets out how it judges a claim, and the reference library keeps the longer case against the whole idea.
Chapter 2: How to trust this bookThe case against, topic by topic